Patent Publication Number: US-2023149048-A1

Title: Systems and methods for vertebral adjustment

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/270,976, filed Feb. 8, 2019, which is a continuation of U.S. patent application Ser. No. 15/048,928 (now U.S. Pat. No. 10,238,427), filed Feb. 19, 2016, which claims the benefit of priority of U.S. Provisional Application No. 62/118,411, filed Feb. 19, 2015, the entire contents of which are hereby incorporated by reference into this disclosure as if set forth fully herein. 
    
    
     FIELD 
     The present disclosure relates to systems and methods for distraction within the human body. In particular, the present invention relates to distraction devices for the adjustment of sagittal curvature in a spine. 
     BACKGROUND 
     Degenerative disc disease affects 65 million Americans. Up to 85% of the population over the age of 50 will suffer from back pain each year. Degenerative disc disease is part of the natural process of aging. As people age, their intervertebral discs lose their flexibility, elasticity, and shock absorbing characteristics. The ligaments that surround the disc, known as the annulus fibrosis, become brittle and are more easily torn. At the same time, the soft gel-like center of the disc, known as the nucleus pulposus, starts to dry out and shrink. The combination of damage to the intervertebral discs, the development of bone spurs, and a gradual thickening of the ligaments that support the spine can all contribute to degenerative arthritis of the lumbar spine. 
     When degenerative disc disease becomes painful or symptomatic, it can cause several different symptoms, including back pain, leg pain, and weakness that are due to compression of the nerve roots. These symptoms are caused by the fact that worn out discs are a source of pain because they do not function as well as they once did, and as they shrink, the space available for the nerve roots also shrinks. As the discs between the intervertebral bodies start to wear out, the entire lumbar spine becomes less flexible. As a result, people complain of back pain and stiffness, especially towards the end of each day. 
     Depending on its severity and condition, there are many ways to treat degenerative disc disease patients with fusion being the most common surgical option. The estimated number of thoracolumbar fixation procedures in 2009 was 250,000. Surgery for degenerative disc disease often involves removing the damaged disc(s). In some cases, the bone is then permanently joined or fused to protect the spinal cord. There are many different techniques and approaches to a fusion procedure. Some of the most common are Anterior Lumbar Interbody Fusion (ALIF), Posterior Lumbar Interbody Fusion (PLIF), Transforaminal Lumbar Interbody Fusion (TLIF), Direct Lateral Interbody Fusion (DLIF), eXtreme Lateral Interbody Fusion (XLIF) (lateral), etc. Almost all these techniques now involve some sort of interbody fusion device supplemented with posterior fixation (i.e., 360 fusion). 
     Another spinal malady that commonly affects patients is stenosis of the spine. Stenosis is related to degeneration of the spine and typically presents itself in later life. Spinal stenosis can occur in a variety of ways in the spine. Most cases of stenosis occur in the lumbar region (i.e., lower back) of the spine although stenosis is also common in the cervical region of the spine. Central stenosis is a choking of the central canal that compresses the nerve tissue within the spinal canal. Lateral stenosis occurs due to trapping or compression of nerves after they have left the spinal canal. This can be caused by bony spur protrusions, or bulging or herniated discs. 
     Non-invasively adjustable devices of the type presented may also be used in patients having scoliosis, spondylolisthesis, Scheuermann&#39;s kyphosis, limb length deformity, limb angle deformity, limb rotational deformity, macrognathia, high tibial osteotomy, or other orthopedic deformities. 
     SUMMARY 
     The present disclosure provides various systems for non-invasively adjusting the curvature of a spine. One or more embodiments of those systems include a housing having a first end and a second end and a cavity between the first end and the second end, a first rod having a first end telescopically disposed within the cavity of the housing along a first longitudinal axis at the first end of the housing and having a first threaded portion extending thereon, and a second end configured to be coupled to a first portion of a spinal system of a subject, a second rod having a first end telescopically disposed within the cavity of the housing along a second longitudinal axis at the second end of the housing and having a second threaded portion extending thereon, and a second end configured to be coupled to a second portion of the spinal system of the subject, a driving member rotatably disposed within the cavity of the housing and configured to be activated from a location external to the body of the subject, a first interface rotationally coupling a first threaded driver to the driving member, the first threaded driver threadingly engaging the first threaded portion of the first rod, a second interface rotationally coupling a second threaded driver to the driving member, the second threaded driver threadingly engaging the second threaded portion of the second rod, and wherein rotation of the driving member in a first direction causes the first threaded driver to move the first end of the first rod into the cavity of the housing along the first longitudinal axis and causes the second threaded driver to move the first end of the second rod into the cavity of the housing along the second longitudinal axis. 
     The present disclosure further provides for a method for adjusting the curvature of a spine includes providing a non-invasively adjustable system including a housing having a first end and a second end and a cavity extending between the first end and the second end, a first rod having a first end telescopically disposed within the cavity of the housing along a first longitudinal axis at the first end of the housing and having a first threaded portion extending thereon, and a second end configured to be coupled to a first portion of a spinal system of a subject, a second rod having a first end telescopically disposed within the cavity of the housing along a second longitudinal axis at the second end of the housing and having a second threaded portion extending thereon, and a second end configured to be coupled to a second portion of the spinal system of the subject, a driving member rotatably disposed within the cavity of the housing and configured to be activated from a location external to the body of the subject, a first interface rotationally coupling a first threaded driver to the driving member, the first threaded driver threadingly engaging the first threaded portion of the first rod, and a second interface rotationally coupling a second threaded driver to the driving member, the second threaded driver threadingly engaging the second threaded portion of the second rod, wherein rotation of the driving member in a first direction causes the first threaded driver to move the first end of the first rod into the cavity of the housing along the first longitudinal axis and causes the second threaded driver to move the first end of the second rod into the cavity of the housing along the second longitudinal axis; creating an opening in the skin of a patient as part of a lumbar fusion surgery; coupling the second end of the first rod to a dorsal portion of a first vertebra of the patient; coupling the second end of the second rod to a dorsal portion of a second vertebra of the patient; and closing or causing to close the opening in the skin of the patient. 
     The present disclosure still further provides for s system for adjusting the curvature of a spine includes a housing having a first end and a second end and a cavity between the first end and the second end, a first rod having a first end telescopically disposed within the cavity of the housing along a first longitudinal axis at the first end of the housing and having a first threaded portion extending thereon, and a second end configured to be coupled to a first portion of a spinal system of a subject, a second rod having a first end telescopically disposed within the cavity of the housing along a second longitudinal axis at the second end of the housing and having a second threaded portion extending thereon, and a second end configured to be coupled to a second portion of the spinal system of the subject, a driving member rotatably disposed within the cavity of the housing and configured to be activated from a location external to the body of the subject, a first interface rotationally coupling a first threaded driver to the driving member, the first threaded driver threadingly engaging the first threaded portion of the first rod, a second interface rotationally coupling a second threaded driver to the driving member, the second threaded driver threadingly engaging the second threaded portion of the second rod, and wherein rotation of the driving member in a first direction causes the first threaded driver to move the first end of the first rod into the cavity of the housing along the first longitudinal axis and rotation of the driving member in a second direction, opposite the first direction, causes the second threaded driver to move the first end of the second rod into the cavity of the housing along the second longitudinal axis. 
     The present disclosure even further provides for a method for adjusting the curvature of a spine includes providing a non-invasively adjustable system including a housing having a first end and a second end and a cavity extending between the first end and the second end, a first rod having a first end telescopically disposed within the cavity of the housing along a first longitudinal axis at the first end of the housing and having a first threaded portion extending thereon, and a second end configured to be coupled to a first portion of a spinal system of a subject, a second rod having a first end telescopically disposed within the cavity of the housing along a second longitudinal axis at the second end of the housing and having a second threaded portion extending thereon, and a second end configured to be coupled to a second portion of the spinal system of the subject, a driving member rotatably disposed within the cavity of the housing and configured to be activated from a location external to the body of the subject, a first interface rotationally coupling a first threaded driver to the driving member, the first threaded driver threadingly engaging the first threaded portion of the first rod, and a second interface rotationally coupling a second threaded driver to the driving member, the second threaded driver threadingly engaging the second threaded portion of the second rod, wherein rotation of the driving member in a first direction causes the first threaded driver to move the first end of the first rod into the cavity of the housing along the first longitudinal axis and rotation of the driving member in a second direction, opposite the first direction, causes the second threaded driver to move the first end of the second rod into the cavity of the housing along the second longitudinal axis; creating an opening in the skin of a patient as part of a lumbar fusion surgery; coupling the second end of the first rod to a dorsal portion of a first vertebra of the patient; coupling the second end of the second rod to a dorsal portion of a second vertebra of the patient; and closing or causing to close the opening in the skin of the patient. 
     The present disclosure additionally provides for a system for adjusting the curvature of a spine including a housing having a first end and a second end and a cavity extending therein, a first rod having a first end telescopically disposed within the cavity of the housing along a longitudinal axis at the first end of the housing and having a first threaded portion extending thereon, and a second end configured to be coupled to a first vertebra of a spinal system of a subject, a driving member rotatably disposed within the cavity of the housing and configured to be activated from a location external to the body of the subject, a second rod extending in a direction generally parallel to the longitudinal axis, the second rod having a first end coupled to the housing and a second end configured to be coupled to a second vertebra of the spinal system of the subject, the second vertebra immediately adjacent the first vertebra, and wherein the direction from the first end to the second end of the first rod is generally parallel to the direction from the first end to the second end of the second rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows an embodiment of a spinal adjustment implant. 
         FIG.  2    is a side view of the spinal adjustment implant of  FIG.  1   . 
         FIG.  3 A  is a cross-sectional view of the spinal adjustment implant of  FIG.  2   , taken along line  3 - 3 . 
         FIGS.  3 B and  3 C  are enlarged views of the spinal adjustment implant of  FIG.  3 A  taken from circles  3  B and  3  C, respectively. 
         FIG.  4    is an embodiment of an external remote controller for use with an implantable device. 
         FIG.  5    shows the internal components of a handpiece of the external remote controller of  FIG.  4   . 
         FIGS.  6 A- 6 D  show embodiments of spinal adjustment implants, some being coupled to lumbar vertebrae. 
         FIG.  7    is a radiographic image of a spinal fusion segment. 
         FIG.  8    shows another embodiment of a spinal adjustment implant. 
         FIG.  9    shows an embodiment of a spinal adjustment implant having a pivotable interface. 
         FIG.  10    shows another embodiment of a spinal adjustment implant. 
         FIG.  11    is a side view of the spinal adjustment implant of  FIG.  10   . 
         FIG.  12    is a cross-sectional view of the spinal adjustment implant of  FIG.  11   , taken along line  12 - 12 . 
         FIGS.  13 - 16    schematically illustrate various embodiments of a driving element of a non-invasively adjustable spinal implant. 
         FIG.  17    shows another embodiment of a spinal adjustment implant. 
         FIGS.  18 - 19    are sectional views of the implant of  FIG.  17   , taken along line  18 - 18 . 
         FIG.  20    illustrates two devices of the embodiment shown in  FIG.  19    secured to the spinal column in series and having a shared base between them. 
         FIGS.  21 A- 21 D  illustrate an embodiment of a spinal adjustment implant including a worm gear and a linkage system that are configured to adjust the lordotic angle of a vertebra system. 
         FIG.  22 A  illustrates the spinal adjustment implant of  FIGS.  21 A- 21 D  secured to a plurality of vertebra of the spinal system. 
         FIGS.  22 B- 22 C  illustrate the implanted spinal adjustment implant of  FIG.  22 A  before and after actuation of a drive member that adjusts the lordotic angle of the attached vertebra. 
         FIGS.  22 D- 22 E  illustrate an enlarged view of the implanted spinal adjustment implant of  FIG.  22 A  before and after actuation of a drive member that adjusts the lordotic angle of the attached vertebra. 
         FIG.  23 A  illustrates an embodiment of a spinal adjustment implant including one or more gear modules. 
         FIG.  23 B  shows the internal components of the spinal adjustment implant of  FIG.  23 A . 
         FIG.  23 C  shows a gear module and other internal components of the spinal adjustment implant of  FIGS.  23 A and  23 B . 
         FIGS.  24 A-D  illustrate another embodiment of the spinal adjustment implant. 
         FIG.  25 A  illustrates an embodiment of a spinal adjustment implant including a Torsen differential that is configured to adjust the lordotic angle of a vertebra system. The Torsen differential allows a drive member to drive the two ends of the spinal adjustment implant at the same or different rate to provide for the same or different displacement rate or angulation rate of change. 
         FIG.  25 B  illustrates a top view of the spinal adjustment implant of  FIG.  25 A  where the internal gears and drive systems of the spinal adjustment implant are visible. 
         FIG.  25 C  illustrates a perspective view of the spinal adjustment implant of  FIG.  25 A  with the housing removed. 
         FIG.  25 D  illustrates an enlarged view of the Torsen differential of the spinal adjustment implant of the  FIG.  25 A . 
         FIG.  25 E  illustrates a cross-sectional view of the spinal system with the spinal adjustment implant of  FIG.  25 A  attached and indicating the angles of rotation of the spinal adjustment implant. 
         FIGS.  26 A- 26 H  illustrate a motor or magnet is able to intermittently lock o unlock a mechanism, as it is adjusted. In some embodiments, the unlocking may temporarily allow for change in angulation, which is then locked again, after the change occurs. 
         FIG.  27    illustrates a hydraulic activated adjustment structure for use in an adjustable spinal implant. 
         FIG.  28    illustrates a magnetic fluid pump activated adjustment structure for use in an adjustable spinal implant. 
         FIG.  29    illustrates a composite fluid coil spring assembly with a skeleton structure. 
         FIG.  30    illustrates a composite fluid coil spring assembly with a compression spring. 
         FIGS.  31 A- 31 C  illustrate different types of springs that may be incorporated, for example into the embodiment of  FIG.  30   , to vary the application of force as conditions are varied. 
         FIG.  32    illustrates an implant having a Nitinol spring. 
         FIG.  33    illustrates an implant having a magnetically operated rotational ratchet. 
         FIGS.  34 A and  34 B  show various embodiments of harmonic drives that may be used together with any of the embodiments described herein. 
         FIG.  35 A  is an exploded view of a cycloidal drive that may be used together with any of the embodiments described herein. 
         FIG.  35 B  is an assembled view of the embodiment illustrated in  FIG.  35 A . 
         FIG.  36    shows an embodiment of a roller screw drive that may be used together with any of the embodiments described herein. 
         FIG.  37    shows a cut-away view of a spur gear that may be used together with any of the embodiments described herein. 
         FIG.  38    shows a cut-away view of a Torsen-type differential, or worm gear, that may be used together with any of the embodiments described herein. 
         FIG.  39    shows a differential screw that may be used together with any of the embodiments described herein. 
         FIGS.  40 A- 40 C  illustrate various embodiments of clutches which may be used together with any of the embodiments described herein. 
         FIG.  41    shows a partial cut-away and partial cross-sectional view of a ball screw mechanism that may be used together with any of the embodiments described herein. 
         FIGS.  42 - 44    are flow charts, illustrating embodiments of systems of torque split, differential, and/or gear reduction. 
         FIGS.  45 A- 45 C  show various pivots for coupling rods to pedicle screws. 
         FIGS.  46 A and  46 B  are detailed views of an embodiment of a pivot having a sprag clutch. 
         FIG.  47    shows another embodiment of a pivot coupled to pedicle screws and vertebrae. 
         FIG.  48    illustrates an embodiment of a torque-limiting brake is configured to lock and unlock a pivot. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the present invention provide for implantable and adjustable devices that provide fixation and non-invasive adjustment of the sagittal curvature of the spine. Sagittal imbalance can be a negative aftereffect of some spinal fusion surgeries. Patient satisfaction with surgery has been correlated with proper restoration of sagittal balance—patients having a sagittal imbalance have been known to express dissatisfaction with their surgery. Spinal fusion surgeries generally involve at least: adding a bone graft material, e.g., an interbody graft, to at least a portion of the spine (e.g., one of more segments or vertebrae of the spine); precipitating a physiologic response to initiate bone ingrowth (e.g., causing osteogenesis into or from or through the bone graft material); and causing a solid bony fusion to form thereby stopping motion or fusing the portion of the spine being treated. If compression of the interbody graft is not maintained during/after fusion surgery, instability and/or non-union may result. Furthermore, if lumbar lordosis is not maintained during/after fusion surgery, sagittal balance may be compromised, leading to potential muscle fatigue and pain, among other potential consequences. In some cases, the sagittal balance may be sufficiently compromised to merit/require revision surgery. Proximal junctional kyphosis (insufficient lumbar lordosis) is a common reason for repeat surgeries. There is a high incidence of insufficient or lower-than-desired lordosis after lumbar fusion surgery. In fact, it has been estimated that about 12% of spines having adjacent segment pathology (sometimes called “flat back syndrome” or “lumbar flat back syndrome”) require repeat, revisionary surgery. Some embodiments of the present invention may be used to non-invasively maintain or change the magnitude of compression between two vertebrae. For example, following a fusion surgery (post-operatively) and/or non-invasively changing the magnitude of lordosis. This may be done to maintain a desired degree of lordosis or to regain a desired degree of lordosis after it has been lost. It may also be done to achieve the desired degree of lordosis when post-surgical studies (e.g., medical imaging) demonstrate that the desired degree of lordosis was not achieved during surgery (e.g., fusion surgery). Some embodiments of the systems and devices disclosed herein can be used to increase the success of fusion, reduce pseudo-arthrosis (e.g., non-union), and/or increase or preserve sagittal balance. “Fine tuning” the magnitude of compression and/or degree of lordosis may allow for reduced symptoms in portions of the spine, such as those adjacent to the fusion. 
       FIGS.  1 - 3 C  illustrate a spinal adjustment implant  500  for implantation along or attachment/coupling to the spinal system of a subject (e.g., one or more vertebrae). In some cases, the subject may be a patient having degenerative disc disease that necessitates fusion of some or all of the lumbar vertebrae through fusion surgery. The spinal adjustment implant  500  can be used in place of traditional rods, which are used to maintain posterior decompression and stabilize during fusion surgery. Some embodiments of the spinal adjustment implant  500  are compatible with interbody spacers placed between the vertebrae being treated. 
     The spinal adjustment implant  500  includes a housing  502  having a first end  504  and a second end  506 . The housing  502  that has a cavity  508  generally defining an inner wall  510  and extending between the first end  504  of the housing  502  and the second end  506  of the housing  502 . The cavity  508  may have a variable inner diameter along its length (e.g., the inner diameter of the cavity  508  changes along its length) or may have a generally constant inner diameter. Variable inner diameter cavities  508  may include one or more ledges, steps, abutments, ramps, chamfered or sloped surfaces, and/or radiused or rounded surfaces, which may be used and/or helpful to hold inner components of the spinal adjustment implant  500 , as will be discussed in further detail, below. In some embodiments, the inner wall  510  of the housing  502  has circumferential grooves and/or abutments  512  that axially maintain certain elements of the assembly (e.g., internal elements). In some embodiments, the abutments  512  include one or more retaining rings or snap rings. 
     A driving member  514  may be disposed, placed, or located within the cavity  508  (e.g., rotatably disposed). In some embodiments, the driving member  514  includes a non-invasively rotatable element, such as described with respect to  FIGS.  20 - 23   . As illustrated in  FIG.  3 A , the driving member  514  may include a cylindrical, radially-poled permanent magnet  516  secured within a first magnet housing  518  and a second magnet housing  520 . The radially-poled permanent magnet may be a cylindrical or partially cylindrical rare earth magnet and may have two poles, four poles, or more. The permanent magnet may be constructed from rare earth magnet materials, such as Neodymium-Iron-Boron (Nd—Fe—B), which have exceptionally high coercive strengths. The individual magnets may be enclosed within a stainless steel casing or various layers of nickel, gold or copper plating to protect the magnet material from the environment inside the body (or vice versa). In certain embodiments, other magnetic materials may be used, including, but not necessarily limited to, SmCo 5  (Samarium Cobalt) or AlNiCo (Aluminum Nickel Cobalt). In other embodiments, Iron Platinum (Fe—Pt) magnets may be used. Iron platinum magnets achieve a high level of magnetism without the risk of corrosion, and may possibly preclude the need to encapsulate. In yet other embodiments, the permanent magnet may be replaced by magnetically responsive materials such as Vanadium Permendur (also known as Hiperco). 
     The first and second magnet housings  518 ,  520  may, together, provide an internal cavity to hold the cylindrical, radially-poled, permanent magnet  516 . In some embodiments, the internal cavity created by the housings  518 ,  520  is longer than the length of the cylindrical, radially-poled, permanent magnet  516 , thus leaving at least some longitudinal space  522 . In other embodiments, the internal cavity is substantially the same side as the cylindrical, radially-poled, permanent magnet  516 . The first and second magnet housings  518 ,  520  may be welded or bonded to each other, as well as to the cylindrical, radially-poled, permanent magnet  516 . These two design features (i.e., 1. an internal cavity that is longer than the magnet, and 2. a first and second housing that are fixed to each other and/or the magnet) may together serve to limit or eliminate compressive and/or tensile stresses on the cylindrical, radially-poled permanent magnet  516 . The first and second magnet housings  518 ,  520  may be made from robust materials (e.g., titanium alloys) in order to provide strength at a comparatively small wall thickness. Of course, as will be readily understood, any of a number of other materials may be used. 
     In the embodiment of  FIGS.  1 - 3 A , the driving member  514  (e.g., drive system, actuator, motor, driver) is positioned longitudinally between two abutments  512  by two radial bearings  524 , which facilitate free rotation of the driving member  514  about a driving member axis  526 . In some embodiments, the abutments  512  incorporate a cornered surface, such as, for example, ledges, steps, corners, etc. In other embodiments, the abutments  512  incorporate a flat or curved surface, including, for example, ramps, chamfered or sloped surfaces, and/or radiused or rounded surfaces. In some embodiments, one or more of the radial bearings  524  are replaced by thrust bearings and/or angular bushings. In some embodiments, the bearings comprise stainless steel. In some embodiments, the bearings comprise 400 series stainless steel. In some embodiments, the bearings comprise electro-polished 316 stainless steel, PEEK, or a combination of these. Forming the bearings out of PEEK and/or plating the bearings may increase efficiency by as much as about 50% or up to about 80% or more. Depending on the locations of the abutments  512 , the bearings may advantageously serve to minimize axial stresses on one or more portions of the drive train of the spinal adjustment implant  500 , including, but not limited to one or more of the radially-poled permanent magnet  516 , the housings  518 ,  520 , the lead screw(s) (to be discussed in additional detail, below), the connection(s) between the magnet and the lead screw (i.e., the pin-based connection). Additionally, the bearings generally allow the system to minimize frictional resistance, thereby reducing the amount of torque required to operate the system, or increasing the possible resultant amount of torque/force that can be generated. 
     Referring to  FIGS.  3 A- 3 C , a first threaded driver  528  (e.g., a lead screw, a screw, a threaded rod, a rotating driver) is connected to the first magnet housing  518  and, therefore, also, the cylindrical, radially-poled permanent magnet  516 . In some embodiments the first threaded driver  528  is connected to the first magnet housing  518  using a connection that allows some axial movement, play, or slop between the two (e.g., leaving the two not axially over-constrained). For example, the first threaded driver,  528  may have a hole  532  (e.g., aperture, port, opening) extending substantially horizontally through the first end  530  of the first threaded driver,  528 . In much the same way, the first magnet housing  518  may have one or more holes  534  (e.g., aperture, port, opening) extending substantially horizontally therethrough, for example, through an annular projection  538 . The hole  532  in the first end  530  may be configured so that it may align with the one or more holes  534  in the annular projection  538 . A holder, such as a pin  536  or other fixer, can extend though the one or more holes  534  in the annular projection  538  and the hole  532  in the first end  530  of the first threaded driver,  528 , thus creating an interface  540  which rotationally couples the driving member  514  to the first threaded driver  528 . In some embodiments, the annular projection  538  and the first end  530  are otherwise rotationally coupled. 
     In much the same way, a second threaded driver  542  (e.g., a lead screw, a screw, a threaded rod, a rotating driver) is connected to the second magnet housing  520  and, therefore, also, the cylindrical, radially-poled permanent magnet  516 . In some embodiments the second threaded driver  542  is connected to the second magnet housing  520  using a connection that allows some axial movement, play, or slop between the two (e.g., leaving the two not axially over-constrained). For example, the second threaded driver  542  may have a hole  546  (e.g., aperture, port, opening) extending substantially horizontally through the first end  544  of the second threaded driver  542 . Similarly, the second magnet housing  520  may have one or more holes  548  (e.g., aperture, port, opening) extending substantially horizontally therethrough, for example, through an annular projection  550 . The hole  546  in the second end  544  may be configured so that it may align with the one or more holes  548  in the annular projection  550 . A holder, such as a pin  552  or other fixer, can extend though the one or more holes  548  in the annular projection  550  and the hole  546  in the first end  544  of the second threaded driver  542 , thus creating an interface  554  which rotationally couples the driving member  514  to the second threaded driver  542 . In some embodiments, the annular projection  550  and the first end  544  are otherwise rotationally coupled. 
     In some embodiments, the driving member  514  is directly, mechanically coupled to one or both of the first threaded driver  528  and the second threaded driver  542 , such as was described above with respect to the cup and pin structure of the pin and annular flange. However, in other embodiments, the driving member  514  is indirectly coupled to one or both of the first threaded driver  528  and the second threaded driver  542 , such as through a gearing system or another type of step down. Gearing systems may advantageously decrease the torque required to generate a given force. In embodiments in which the driving member  514  is directly, mechanically coupled to one or both of the first threaded driver  528  and the second threaded driver  542 , rotation of the driving member  514  in first rotational direction  556  causes the rotation of both the first threaded driver  528  and the rotation of the second threaded driver  542  in the same direction, i.e., the first rotational direction  556 . In the same way, rotation of the driving member  514  in second rotational direction  559  causes the rotation of both the first threaded driver  528  and the rotation of the second threaded driver  542  in the same direction, i.e., the second rotational direction  559 . Though the first and second threaded drivers  528 ,  542  are illustrated in this embodiment as being screws with male threads, in other embodiments, they may also be hollow rods having internal (female) threads along at least a portion of their length (e.g., all or less than all). 
     With continued reference to  FIGS.  1 - 3 A , the first threaded driver  528  and the second threaded driver  542  may have opposite thread handedness. The first threaded driver  528  may have a right-handed male thread  560 . A first rod  558  (e.g., extendible or retractable portion) has a first end  562  telescopically disposed within the cavity  508  of the housing  502 , and a second end  564  configured to be coupled to a portion a patient, such as, for example, a portion of the skeletal system. In some embodiments, as illustrated in  FIGS.  1 - 3 A , the second end  564  of the first rod  558  is configured to be coupled to a first portion of the skeletal system, such as, but not limited to a first portion of the spinal system (e.g., a first vertebra), via a first extension member  566 . The first portion of the spinal system may be a first vertebra. Alternatively, the second end  564  of the first rod  558  may be coupled to a first vertebra directly, via one or more of: a pedicle screw; hook; wire; or other attachment system(s). As shown in  FIGS.  1 - 3 A , the first extension member  566  may comprise a rod portion  568  and a base portion  570 . The base portion  570  may be secured to the second end  564  of the first rod  558  using a set screw  572  (e.g., by tightening the set screw  572 ) or other fastener/fastening device. A flat portion  573  may be located on a portion of the first rod  558 , in order to provide a surface for interfacing with an end of the set screw  572 , for example, to improve resistance to loosening of the set screw  572  with respect to the first rod  558 . The rod portion  568  of the first extension member  566  may be coupled to a first vertebra directly, via one or more of: a pedicle screw; hook; wire; or other attachment system(s). As may be seen in  FIG.  6 A , the first extension member  566  a may extend generally transversely with respect to the housing  502  and/or first rod  558   a.    
     Referring again to  FIGS.  1 - 3 A , the first end  562  of the first rod  558  may include a cavity  574  having a first threaded portion  576  incorporating a right-handed female thread  580  configured to mate with the right-handed male thread  560  of the first threaded driver  528 . In some embodiments, one of which is shown in  FIG.  3 C , the cavity  574  comprises a nut  578  bonded or otherwise secured therein. The right-handed male thread  560  of the first threaded driver  528  and the right-handed female thread  580  of the first rod  558  threadingly engage each other such that rotation of the driving member  514  in the first rotational direction  556  causes the first threaded driver  528  to turn in the same first rotational direction  556 , thereby causing the first rod  558  to move into the cavity  508  of the housing  502  along a first longitudinal axis  582  ( FIG.  1   ), in a first longitudinal direction  584 . 
     The second threaded driver  542  may comprise a left-handed male thread  586 . A second rod  588  (e.g., extendible or retractable portion) has a first end  590  telescopically disposed within the cavity  508  of the housing  502 , and a second end  592  configured to be coupled a portion a patient, such as, for example, a portion of the skeletal system. In some embodiments, as illustrated in  FIGS.  1 - 3 A , the second end  592  of the second rod  588  is configured to be coupled to a second portion of the spinal system via a second extension member  594 . The second portion of the spinal system may be a second vertebra. Alternatively, the second end  592  of the second rod  588  may be coupled to a second vertebra directly, via one or more of: a pedicle screw; hook; wire; or other attachment system. As shown in  FIGS.  1 - 3 A , the second extension member  594  may comprise a rod portion  596  and a base portion  598 . The base portion  598  may be secured to the second end  592  of the second rod  588  using a set screw  599  (e.g., by tightening the set screw  599 ). The rod portion  596  of the second extension member  594  may be coupled to a second vertebra directly, via one of more of: a pedicle screw; hook; wire; or other attachment system. As may be seen in  FIG.  6 A , the second extension member  594  a may extend in a generally transversely with respect to the housing  502  a and/or second rod  588  a. Referring again to  FIGS.  1 - 3 A , the first end  590  of the second rod  588  may include a cavity  597  having a first threaded portion  595  incorporating a left-handed female thread  593 . In some embodiments, one of which is shown in  FIG.  3 B , the cavity  597  comprises a nut  591  bonded or otherwise secured therein. The left-handed male thread  586  of the second threaded driver  542  and the left-handed female thread  593  of the second rod  588  threadingly engage each other such that rotation of the driving member  514  in the first rotational direction  556  causes the second threaded driver  542  to turn in the same first rotational direction  556 , thereby causing the second rod  588  to move into the cavity  508  of the housing  502  along a second longitudinal axis  589  ( FIG.  1   ), in a second longitudinal direction  587 . 
     The driving member  514  in combination with the first threaded driver  528  and the second threaded driver  542  may therefore comprise a turnbuckle, such that their rotation in the first rotational direction  556  causes both the first rod  558  and second rod  588  to move into the cavity  508  of the housing  502 , thus causing the longitudinal distance L between points A and B to decrease. This motion is capable of generating a force on the spine at the points of attachment and increasing the compressive force(s) between vertebrae. Rotation of the driving member  514 , first threaded driver  528  and second threaded driver  542  in a second rotational direction  559 , opposite the first rotational direction  556 , causes both the first rod  558  and second rod  588  to move out of the cavity  508  of the housing  502 , thus causing the longitudinal distance L between points A and B to increase. This motion is capable of generating a force on the spine at the points of attachment and decreasing the compressive force(s) between vertebrae. 
     In some embodiments, the first threaded driver  528  and the second threaded driver  542  may have the same thread handedness. Both the first threaded driver  528  and the second threaded driver  542  may have a right-handed male thread. Alternatively, both the first threaded driver  528  and the second threaded driver  542  may have a left-handed male thread. As described above, when the first threaded driver  528  and the second threaded driver  542  have opposite thread handedness, rotation of the two in the same direction (such as by rotation of the cylindrical, radially-poled, permanent magnet) will cause the first threaded driver  528  and the second threaded driver  542  to move in opposite directions—depending on the right or left thread handedness, rotation in a first direction will cause both threaded drivers to retract into the housing while rotation in the second, opposite direction will cause both threaded drivers to distract from or extend out of the housing. By contrast, when both the first threaded driver  528  and the second threaded driver  542  have an identical thread handedness (i.e., both right or both left) rotation of the cylindrical, radially-poled, permanent magnet will cause the first and second threaded drivers to move in opposite directions with respect to the housing—depending on the right or left thread handedness, rotation in a first direction will cause the first threaded driver  528  to retract into the housing while causing the second threaded driver  542  to distract from or extend out of the housing (assuming the other or the right or left thread handedness, rotation in the opposite, second direction will cause the first threaded driver  528  to distract from or extend out of the housing while causing the second threaded driver  542  to retract into the housing). As will be discussed in more detail below, a third extension member  581  having a rod portion  579  and a base portion  577  may be reversibly or fixedly coupled to the housing  502 . For example, the base portion  577  may be secured to the housing  502  by tightening a set screw  575 . 
     The driving member  514  in combination with the first threaded driver  528  and the second threaded driver  542  may therefore selectively generate a force between two vertebrae (e.g., the vertebrae to which the first extension member  566  and the third extension member  581  are attached) while decreasing the force between the two adjacent vertebrae (e.g., the vertebrae to which the third extension member  581  and the second extension member  594  are attached). In effect, such a system can move a top (or bottom) vertebra closer to a middle vertebra, while moving a bottom (or top) vertebra away from the middle vertebra. Rather than causing motion, this system (as well as any of the other systems disclosed herein) may generate force without causing motion. Though, it is likely that at least some motion will accompany the generation of force, whether it be a distraction force or a compressive force. 
     To seal the interior contents of the cavity  508  of the housing  502 , seals  585 , for example, dynamic seals, (shown in  FIGS.  3 B- 3 C ) may be disposed between each of the first and second rods  558 ,  588  and the housing  502 . The dynamic seals  585  may comprise o-rings, and may be contained within a circumferential groove on either the exterior of the rods  558 ,  588  or the interior of the housing  502 . Of course, many other sealing systems are contemplated, such as but not limited to expandable hydrogel-based systems, bellows or flexible sheaths covering the overlap of the housing and the rod(s), etc. 
     In some embodiments, one or more of the housing and the rods has an anti-rotation member or a key to prevent rotation of the housing with respect to the rods (and therefore the third extension member  581  with respect to one or both of the first and second extension members  566 ,  594 ). For example, in some embodiments, the housing  502  has a protrusion (not shown) configured to engage longitudinal grooves  583  on the rods  558 ,  588 . The protrusion maintains rotational alignment of each of the rods  558 ,  588  with respect to the housing  502  and allows the rods  558 ,  588  to move (e.g., extend and extend, retract and retract, extend and retract, or retract and extend) longitudinally with respect to each other while preventing significant rotation with respect to one another. In some embodiments, the anti-rotation member or element prevents substantially all rotational movement of the housing with respect to the rods (or vice versa). In other embodiments, the anti-rotation member or element prevents all rotational movement of the housing with respect to the rods (or vice versa). In still other embodiments, the anti-rotation member or element prevents less than about 10 degrees, less than about 8 degrees, less than about 6 degrees less than about 4 degrees, or less than about 2 degrees of rotational motion of the housing with respect to the rods (or vice versa). Thus, when the spinal adjustment implant  500  is secured to a fusion patient&#39;s spine, instrumented portions of the spine can be held static to one another, and substantial movement may only occur when the spinal adjustment implant  500  is adjusted. In some embodiments, substantial fixation of the rotational alignment between each of the rods  558 ,  588  and the housing  502  is achieved by a member attached at the end of the housing. In other embodiments, substantial fixation of the rotational alignment between each of the rods  558 ,  588  and the housing  502  is achieved by the rods having non-circular cross-sections (e.g., ovoid, hexagonal, square, a geometric shape, etc.) which are “keyed” to a similarly non-circular cavity (e.g., a mating cavity) within the housing. 
     The second ends  564 ,  592  of the first and second rods  558 ,  588  and the rod portions  568 ,  596  of the first and second extension members  566 ,  594  may be sized similar to standard spinal rods. In this way, the second ends  564 ,  592  of the first and second rods  558 ,  588  and the rod portions  568 ,  596  of the first and second extension members  566 ,  594  may be fixed to the skeletal system or coupled to fixation devices using standard, off-the-shelf orthopedic hardware, such as pedicle screws or otherwise. In some embodiments, the second ends  564 ,  592  of the first and second rods  558 ,  588  and the rod portions  568 ,  596  of the first and second extension members  566 ,  594  have transverse dimensions, or diameters, in the range of about 3-7 mm, in the range of about 3.5-6.35 mm, greater than about 3.5 mm, greater than about 4.5 mm, or greater than about 5.5 mm. The housing  502  may be coupled to a third portion of the spinal system, for example, a third vertebra via a third extension member  581  having a rod portion  579  and a base portion  577 . The base portion  577  may be secured to the housing  502  by tightening a set screw  575 . Of course, it will be understood that, while adjustability can be advantageous in some applications, in other applications, any one or more of the first, second, and third extension member may be permanently fixed to the housing and/or the rods (for example, by welding, monolithic formation, or otherwise). 
     A system incorporating the spinal adjustment implant  500  according to various embodiments of the present invention, may use an External Remote Controller (ERC).  FIG.  4    illustrates an example of an External Remote Controller (ERC)  180  which may be used to non-invasively control the spinal adjustment implant  500  by means of a magnetic coupling of torque. ERC  180  comprises a magnetic handpiece  178 , a control box  176  (containing a processor) which may be integrated with the handpiece  178  and a power supply  174  such as a battery or external plug for connection to a standard power outlet. The control box  176  includes a control panel  182  having one or more controls (buttons, switches or tactile, motion, audio or light sensors) and a display  184 . The display  184  may be visual, auditory, tactile, the like, or some combination of the aforementioned features, or any other display/UI described in this disclosure. The control box  176  may further contain a transceiver for communication with a transceiver in the implant and/or other external devices. 
       FIG.  5    illustrates an internal assembly  478  of the magnetic handpiece  178  configured for applying a moving magnetic field to allow for non-invasive adjustment of the spinal adjustment implant  500  by turning the cylindrical, radially-poled permanent magnet  516  within the spinal adjustment implant  500 . The cylindrical, radially-poled permanent magnet  516  of the spinal adjustment implant  500  includes a north pole  406  and a south pole  408 . A motor  480  with a gear box  482  outputs to a motor gear  484 . The motor gear  484  engages and turns a central (idler) gear  486 , which has the appropriate number of teeth to turn first and second magnet gears  488 ,  490  at identical rotational speeds. First and second magnets  492 ,  494  turn in unison with the first and second magnet gears  488 ,  490 , respectively. Each magnet  492 ,  494  is held within a respective magnet cup  496  (shown partially). An exemplary rotational speed is 60 RPM or less. This speed range may be desired in order to limit the amount of current density included in the body tissue and fluids, to meet international guidelines or standards. As seen in  FIG.  5   , the south pole  498  of the first magnet  492  is oriented the same as the north pole  404  of the second magnet  494 , and likewise, the first magnet  492  has its north pole  400  oriented the same and the south pole  402  of the second magnet  494 . As these two magnets  492 ,  494  turn synchronously together, they apply a complementary and additive moving magnetic field to the cylindrical, radially-poled permanent magnet  516 . Magnets having multiple north poles (e.g., two or more) and multiple south poles (e.g., two or more) are also contemplated in each of the devices. Alternatively, a single magnet (e.g., a magnet with a larger diameter) may be used in place of the two magnets. As the two magnets  492 ,  494  turn in a first rotational direction  410  (e.g., counter-clockwise), the magnetic coupling causes the cylindrical, radially-poled permanent magnet  516  to turn in a second, opposite rotational direction  412  (i.e., clockwise). The rotational direction of the motor  480  is controlled by buttons  414 ,  416 . One or more circuit boards  418  contain control circuitry for both sensing rotation of the magnets  492 ,  494  and controlling the rotation of the magnets  492 ,  494 . Alternatively, one or more electromagnets may be used in place of or in conjunction with the magnets  492 ,  494 . 
     Two spinal adjustment implants  500   a ,  500   b  coupled bilaterally to three lumbar vertebrae are shown in  FIG.  6 A . The first spinal adjustment implant  500  and second spinal adjustment implant  500   b  may be secured to the spinal system  600  as is described below. The first rod  558  as of the first spinal adjustment implant  500   a  is secured to the L5 lumbar vertebra  602  by a pedicle screw  604   a , while the first rod  558   b  of the second spinal adjustment implant  500   b  is secured to the L5 lumbar vertebra  602  by a pedicle screw  604   b . The second rod  588   a  of the first spinal adjustment implant  500   a  is secured to the L3 lumbar vertebra  608  by a pedicle screw  604   c , while the second rod  588   b  of the second spinal adjustment implant  500   b  is secured to the L3 lumbar vertebra  608  by a pedicle screw  604   d . The first rods  558   a ,  558   b  and second rods  588   a ,  588   b  may be coupled to the pedicle screws  604   a ,  604   b ,  604   c ,  604   d  via first and second extension members  566   a ,  566   b ,  594   a ,  594   b . The housings  502   a ,  502   b  may be secured by pedicle screws  606   a ,  606   b , via third extension members  581   a ,  581   b , to the L4 lumbar vertebra  610 . Such securement of the housings  502   a ,  502  to an intermediary vertebra (L4,  610 ) between the two vertebrae to be adjusted (L5 and L3,  602 ,  608 ) helps assure that the implants  500   a ,  500   b  maintain set locations on the spinal system  600  and can serve as reference points to the adjustment of the first rods  558   a ,  558   b  and second rods  588   a ,  588   b . Adjusting the spinal adjustment implants  500   a ,  500   b  by rotating driving member  514  in the first direction  556  ( FIG.  3 A ) increases compression on and between the L5 lumbar vertebra  602  and L3 lumbar vertebra  608 . Increasing compression on implants such as those shown in  FIG.  6    may advantageously increase lordosis in the sagittal plane. The spinal adjustment implants  500   a ,  500   b  may be secured to the dorsal (posterior) side of the vertebrae  602 ,  608 ,  610 . In such an implantation configuration, when the implants  500   a ,  500   b  decrease in length (causing compression), the dorsal sides of the vertebrae  602 ,  608 ,  610  (the locations of pedicle screw insertion) may be brought closer together than the anterior (ventral) sides of the vertebrae  602 ,  608 ,  610  (opposite the side of pedicle screw insertion). That differential displacement increases the angle of lordosis. 
       FIG.  6 B  illustrates an embodiment of an adjustment implant. The implant includes a housing  650 . In some embodiments, the housing is formed monolithically. However, in other embodiments, the housing is formed from two halves joined at a joint (e.g., a threaded or welded joint)  651 . Using a housing formed from two halves may advantageously ease the manufacturing and assembly process, particularly for parts, such as the thrust bearings, which are held by features of the inner wall of the housing (such as abutments). The implant also includes a first rod  660  and a second rod  661 . 
     The first rod  660  has a proximal end that is at least partially contained within the housing and has a first rod hollow or cavity  662 . The proximal portion of the first rod  660  contained within the housing may have a slot, groove, or other linear feature  666  on at least part of its surface. As will be explained below, the slot  666  may serve as a portion of an anti-rotation system. The first rod  660  also has a distal end that extends away from the housing and is used to attach the device to the skeletal system of a patient/subject. In some embodiments, the rod  660  is straight prior to implantation. In other embodiments, the rod  660  is curved prior to implantation. In yet other embodiments, the rod  660  is bendable prior to or during surgery, for example, by an implanting surgeon, so that the rod may best conform to the individual patient into which it is being implanted. The rod may be fixed directly to the patient&#39;s skeletal system, for example, using standard pedicle screws. Alternatively, the rod  660  may be attached to the patient&#39;s skeletal system using a keyhole extender system that holds the rod  660  some distance away from the skeletal system. The keyhole extender system may include a ring  664  off of which a shaft or bar extends. The ring  664  may be slid up and down the rod  660 , thereby improving adjustability. Once the desired position of the ring  664  is identified, it may be reversibly fixed to the rod  660  using a set screw  670 . 
     The proximal end of the first rod  660  has an outer diameter that is just smaller than an inner diameter of the housing  650 . In that way, a seal may be formed by using conventional methods, such as o-rings.  FIG.  6 B  shows an annular groove containing an o-ring on an outer surface of the proximal end of the first rod  660 . However, it should be understood that a groove for containing an o-ring may be included on the inner surface of the housing. 
     The housing  650  may be hollow across its entire length. However, while the housing  650  may be hollow, the inner diameter may change across its length. For example, the housing  650  may include one or more corners, steps or abutments to hold one or more internal features of the device, such as portion(s) of the drive train, for example one or more bearing (e.g., thrust bearings and/or radial bearings). As shown in  FIG.  6 B , the housing  650  includes a step or abutment that holds a radial bearing, which, in turn, holds axially a spindle of the rotating magnet  652  (e.g., a spindle of a housing holding the magnet  652 , or a spindle that extends through and is axially fixed with respect to the magnet  652 ). The housing  650  is also shown as having a set screw, key, or protrusion  646  that mates with the slot to prevent rotation of the rod  660  with respect to the housing  650 . In some embodiments, the rod  660  may have a plurality of slots  666  while the housing has a single protrusion  646 . In that way, the rotational orientation of the rod  660  with respect to the housing  650  may be changed by merely withdrawing the protrusion  646 , rotating the rod  660  until the rod  660  is at the slot  666  closest to the desired rotational orientation, and reinserting the protrusion  646 . 
     As discussed above, the housing  650  holds the rotating magnet  652 . In the embodiment illustrated in  FIG.  6 B , the rotating magnet  652  is coupled to the drive shaft  642  in a one to one manner, such that one rotation of the rotating magnet  652  causes one rotation of the drive shaft  642 . Of course, any number of gearing systems, such as or similar to those described elsewhere herein, may be interposed between the rotating magnet  652  and the drive shaft  642 . In that way, more turns of the rotating magnet  652  may be required to effectuate a full turn of the drive shaft  642 , thereby increasing the torque of the drive shaft  642  by comparison to the rotating magnet  652 . 
     In at least some embodiments, the device shown in  FIG.  6 B  is substantially bilaterally symmetrical from proximal to distal end. Therefore, the opposite elements, such as the second rod  661  and the second drive shaft  643 , may be the same as has already been discussed. 
       FIG.  6 C  illustrates two spinal adjustment implants  620  and  621 , similar to the two spinal adjustment implants  500   a ,  500   b  coupled bilaterally to three lumbar vertebrae shown in  FIG.  6   . The two spinal adjustment implants  620  and  621  share many of the same features as is described with respect to other embodiments disclosed herein. However, rather than being attached to the three lumbar vertebrae using standard pedicle screws, as is shown in  FIG.  6 A , the two spinal adjustment implants  620  and  621  are coupled to the three lumbar vertebrae using a different type of specialized screw having a different head  622 . As can be seen, the heads of the specialized screws  622  are facing to the rear (the same as the pedicle screws shown in  FIG.  6 A ) of the spine. It should be appreciated that any type of screw and head fixture may be used so long as it adequately anchors the extension rods (and therefore the spinal adjustment implants) with respect to the spine. Depending on the length of the extension rods being used to fix the spinal adjustment implants  620  and  621  to the spine, care may need to be taken not to allow excess rod length to impinge on nervous or other critical tissues. In some embodiments, the excess length of the extension rods, on the side of the pedicle screw opposite the spinal implant, may be trimmed so that the extension rod terminates in a surface substantially flush with the outer surface of the pedicle screw housing. 
     While  FIGS.  6 A and  6 C  illustrate two spinal adjustment implants bilaterally implanted next to the spine and attached to the spine using three extension members, each, which are, in turn, fixed to three adjacent vertebrae using pedicle screws and housings. In those figures, the three extension members extend transversely or laterally, and the pedicle screw housings face to the rear of the patient. Stated in another way, the pedicle screws in  FIGS.  6 A and  6 C  are inserted into their respective vertebrae substantially in a posterior-anterior direction.  FIG.  6 D  illustrates the right-lateral spinal adjustment implant from a more frontal viewpoint. While  FIGS.  6 A,  6 C, and  6 D  illustrate the spinal adjustment devices predominantly to the lateral sides of the lumbar spine, it should be understood that the spinal adjustment devices may be placed closer or further away from the spinal midline laterally, or closer or further away from the spinal midline anterior-posteriorly. This may be accomplished through selective placement, including angling, of the pedicle screw as well as inserting the extension member into one side or the other of the pedicle screw housing. 
     Flexion of the first and/or second rods  558   a ,  558   b ,  588   a ,  588   b  may increase the amount of angle increase that can occur during compressive adjustment. In some embodiments, smaller diameter rods are used to increase the possible flexion. In some embodiments, rods having a diameter of less than about 6.5 mm, less than about 5.5 mm less than about 4.5 mm, less than about 3.5 or less than about 2.5 mm are used. In some embodiments, rods comprise PEEK (polyether ether ketone) to increase flexion. In some embodiments, flexible rods comprise a laser-cut structure and/or a Nitinol structure. In  FIG.  7   , the lordotic Cobb angle (angle of Lordosis) a between the L3  608  and L5  602  lumbar vertebrae is shown in a radiographic image of an L3-L5 fusion having first and second interbody spacers  612 ,  614  placed between the vertebral bodies of the L3, L4, and L5 lumbar vertebrae  608 ,  610 ,  602 . Some flexion of the rods  616 ,  618  is shown. It will be understood that because the image is taken laterally, rods  616  and  618  are overlaid and thus appear to be only one rod. But, two rods are actually present. The lordotic Cobb angle may be increased (or decreased) by about 0.5-15°, about 1-13°, about 1.5-11°, about 2-9°, about 2.5-7°, or about 3-5° per level through use of the spinal adjustment implants such as those described above (e.g.,  500   a ,  500   b ) either unilaterally or bilaterally placed in the L3-L5 segments, for a total L3 to L5 angle increase of about 1-30°. 
     In some embodiments, one or more gear modules are placed between the driving member  514  and one or both of the first and second threaded drivers  528 ,  542 , in order to increase the amount of compressive force that may be applied during adjustment. In some embodiments, the gear modules comprise planetary gearing, including possibly one or more of sun gears, ring gears and planet gears. 
     In some embodiments, at least one planetary gear stage (e.g., two, three, four, five, six, or even more planetary gear stages) is included between (operatively coupled to both of and/or between) the permanent magnet and the drive shaft (e.g., drive member, lead screw). Each planetary gear stage can comprise a sun gear and a plurality of planetary gears (e.g., three, four, five, six, or even more planetary gears), which are rotatably held within a frame, e.g., by pins. The sun gear is either a part of the magnet housing (e.g., the sun gear may be directly connected to the magnet/magnet housing), or a part of the gear frame. The rotation of the sun gear causes the planetary gears to rotate and track along inner teeth of a ring gear insert (e.g., a ring gear insert). Each gear stage has a gear reduction ratio (e.g., of 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or even more), which results in a total gear reduction (e.g., a total gear reduction of 64:1—provided by three planetary gear stages each having a reduction ratio of 4:1). The total reduction ratio is merely the individual reduction radios multiplied. Therefore, a planetary gear system having 4 stages, each with a ratio of 3:1 would have a total reduction ratio of (3×3×3×3):(1×1×1×1), or 81:1. It should be understood that other gear reductions, and numbers of stages may be used. 
     In some embodiments, a slip clutch is placed between the driving member  514  and one or both of the first and second threaded drivers  528 ,  542 , in order to set a maximum compressive force that can be applied between the two drivers. In some embodiments, a differential is placed between the driving member  514  and the first and second threaded drivers  528 ,  542  to allow one of the first and second rods  558 ,  588  to continue adjusting after the other rod is no longer able to adjust due to having reached a threshold resistive force. In some embodiments, the differential incorporates differential gears. The differential gears may include, for example, bevel gears, spur gears, worm gears, and/or a Torsen-type differential—such differential gears will be discussed in more detail, below. In some embodiments, one or more thrust bearings is incorporated in order to protect one or more of the driving member  514 , slip clutch(s), gear module(s), and/or differential from excessive stresses. Such thrust bearings may be held substantially fixed with respect to and by the walls of the housing  502 , for example, by ledges, abutments, rings, or other structures incorporated into or extending from the housing  502  (e.g., an inner wall of the housing). 
       FIG.  8    illustrates a spinal adjustment implant  500   a  implanted in an L3-L5 fusion having first and second interbody spacers  612 ,  614  placed between the L3 and L4, and L4 and L5 lumbar vertebrae  608 ,  610 ,  602 , respectively. All of the connections between the rods, extension members and pedicle screws are shown in  FIG.  8    as being fixed. Non-invasive actuation and rotation of the driving member  514  (depending on the thread handedness, in the first rotational direction  556  or the second rotational direction  559  ( FIG.  3 A )) increases compression, e.g., along line C. In combination with flexion of the first and/or second rods, the compressive forces can decrease dorsal distance Dd more than anterior distance Da thereby advantageously increasing the lordotic Cobb angle. 
       FIG.  9    illustrates an embodiment of a spinal adjustment implant  700 . The spinal adjustment implant  700  is similar to the implant  500  of  FIGS.  1 - 3 C and  500     a  of  FIG.  8   , but additionally includes a first pivotable interface  729  between the first rod  758  and pedicle screw  725  and a second pivotable interface  727  between the second rod  788  and pedicle screw  723 . Examples of such pivotable interfaces will be discussed in additional detail below, for example with respect to  FIGS.  45 A- 48   . Such pivotable interfaces allow the pedicle screws and the vertebrae to which they are attached to change angle more easily; consequently, to decrease Dorsal distance Dd more than Anterior distance Da the spinal adjustment implant need not rely on only potential or minor flexion in the extension rods and/or pedicle screws. The first and second pivotable interfaces  729 ,  727  may allow a potentially greater increase in the lordotic Cobb angle during compression than that permitted by the spinal adjustment implant  500   a  of  FIG.  8    (which lacks pivotable interfaces  729 ,  727 ). 
     When the magnitude of compression force C is increased by the spinal adjustment implant  700 , the L5 lumbar vertebra  602  is able to rotate according to or along arc R1 with respect to an axis of rotation  719  of the first pivotable interface  729 . Likewise, the L3 lumbar vertebra  608  is able to rotate according to or along arc R2 with respect to an axis of rotation  721  of the second pivotable interface  727 . In some embodiments, the first and second pivotable interfaces  729 ,  727  are lockable and unlockable to allow free rotation about the axes of rotation  721 ,  719  during adjustment and to inhibit rotation about the axes of rotation  721 ,  719  after adjustment is complete. In some embodiments, the first and second pivotable interfaces  729 ,  727  are non-invasively lockable and unlockable (such as by using a magnetic field to lock and unlock or by using an electromagnetic signal, such as RF, Bluetooth, etc.). In some embodiments the first and second pivotable interfaces  729 ,  727  are configured to be non-invasively lockable and unlockable as part of the non-invasive adjustment. In some embodiments the first and second pivotable interfaces  729 ,  727  are configured to be non-invasively lockable and unlockable in conjunction with the rotation of the driving member  514 . In some embodiments, the pivotable interfaces  729 ,  727  are configured to be intermittently locked and unlocked during an adjustment procedure. 
     In some embodiments, one or more of the pivotable interfaces is configured to rotate freely in either direction (e.g., clockwise and/or counterclockwise). In some embodiments, one or more of the pivotable interfaces is partially constrained to have free rotation in one direction but no rotation in the other direction—this may be accomplished using a free wheel or other one-way clutching. Examples of devices that may be used to allow unidirectional rotational movement are provided below—in some embodiments, a clutch system, ratchet system, or other motion inhibiting device may be used. In some embodiments, the pivotable interfaces include two-way locking so that they may lock and unlock automatically by the operation of the spinal adjustment implant. For example, the External Remote Controller (ERC) may be used to lock and unlock a magnetic lock which is capable of reversibly removing the rotational freedom of the pivotable interface(s). An example of one such device is shown in  FIG.  48   . In some embodiments which may be either freely rotating or lockable, there may additionally by constrained rotation or motion, wherein there are limits, extents, or detents that limit the total amount of travel of a particular rotation or motion. In some embodiments, structural motion limiters may be set prior to implantation. For example, the implanting surgeon might evaluate the patient&#39;s spine and determine that a maximum correction of 10 degrees per pivotable interface (for a total correction of 20 degrees) is all that is needed and/or permissible. In that case, the surgeon may set each physical motion limiter to “10 degrees” (for example, the pivotable interface may have markings or holes identifying the maximum angle of rotation to which the surgeon may move the physical motion limiter). While 10 degrees was used as an example, it should be understood, that any degree may be use—however, physically, the range of correction will generally be less than about 30, less than about 25, less than about 20, less than about 15, less than about 10, or even less than about 5 degrees per pivotable interface. 
       FIGS.  10 - 12    illustrate a spinal adjustment implant  800  for implantation along the spine of a subject. The spinal adjustment implant  800  comprises a housing  802  having a first end  804  and a second end  806 . The housing  802  includes a cavity  808 , which extends between the first end  804  of the housing  802  and the second end  806  of the housing  802 . The cavity  808  may have a variable inner diameter along its length or may have a generally constant inner diameter. The inner wall  810  of the housing  802  may have circumferential grooves or abutments  812 , in order to axially maintain certain elements of the assembly. A driving member  814  is rotatably disposed within the cavity  808 . The driving member  814  may comprise any non-invasively rotatable element, such as those described with respect to  FIGS.  13 - 16   . The embodiment of the driving member  814  illustrated in  FIG.  12    comprises a cylindrical, radially-poled permanent magnet  816  secured within a first magnet housing  818  and a second magnet housing  820 . 
     In the embodiment of  FIGS.  10 - 12   , the driving member  814  is positioned longitudinally between two abutments  812  by two radial bearings  824 , which facilitate free rotation of the driving member  814  about a driving member axis  826 . A first threaded driver  828  has a first end  830  having a shaft  832 , and the first magnet housing  818  has a cylindrical cavity  838 . A first clutch  836  engages the inside of the cylindrical cavity  838 , and inner cavity of the first clutch  836  engages the shaft  832  of the first threaded driver  828 . The first clutch  836  is configured to couple rotational motion between the first magnet housing  818  and the first threaded driver  828  in a first rotational direction  856  when the first magnet housing  818  is turned by the radially-poled permanent magnet  816  in a first rotational direction  856 . But, the first clutch  836  is configured to cause slippage between the first magnet housing  818  and the first threaded driver  828  when the first magnet housing  818  is turned by the radially-poled permanent magnet  816  in a second rotational direction  859  (e.g., opposite the first rotational direction  856 ). 
     A second clutch  842  engages the inside of the cylindrical cavity  844  of the second magnet housing  820 , and inner cavity of the second clutch  842  engages the shaft  846  of the second threaded driver  850 . The second clutch  842  is configured to couple rotational motion between the second magnet housing  820  and the second threaded driver  850  in the second rotational direction  859  when the second magnet housing  820  is turned by the radially-poled permanent magnet  816  in the second rotational direction  859 . But, the second clutch  842  is configured to cause slippage between the second magnet housing  820  and the second threaded driver  850  when the second magnet housing  820  is turned by the radially-poled permanent magnet  816  in the first rotational direction  856 . 
     Incorporation of one-way clutches (e.g., one way clutches  836 ,  842 ) may allow the driving member  814  to be capable of independently driving either the first threaded driver  828  or the second threaded driver  850  depending on which direction (e.g., first rotational direction  856  or second rotational direction  859 ) the driving member  814  is caused to turn. In some embodiments, the first and second clutches  836 ,  842  comprises a number of different types of one-way clutching, including but not limited to a needle clutch, a free wheel, a sprag clutch, a spring clutch, a face gear, or a ratchet. In some embodiments, the radial bearings or thrust bearings are themselves be configured as one-way clutches (e.g., as a hybrid component). Indeed, any of a number of different clutch mechanisms may be used as the one-way clutches  836 ,  842 . Additional examples are discussed in greater detail, below, with respect to at least  FIGS.  40 A- 40 C . 
     The first and second threaded drivers  828 ,  850  have second ends  858 ,  860  having male threads  862 ,  864 , which engage female threads  866 ,  868  of first and second rods  870 ,  872 . In some embodiments, the spinal adjustment implant  800  is configured for compression (i.e., the threads of both of the first and second threaded drivers  828 ,  850  and the female threads  866 ,  868  are right-handed). In other embodiments, the spinal adjustment implant  800  is configured for tension/distraction (i.e., the threads of both of the first and second threaded drivers  828 ,  850  and the female threads  866 ,  868  are left-handed). 
     Extension members  874 ,  876 ,  878  may be configured to couple to the first rod  870 , second rod  872  and housing  802 , respectively. The extension members  874 ,  876 ,  878  may be coupled to pedicle screws (not shown). These extension members may be the same as the many other extension members discussed in detail above. 
     While some illustrated embodiments provide instrumentation to two lumbar levels (L3-L4 and L4-L5), one level only of instrumentation, or greater than two levels of instrumentation are also within the scope of embodiments of the present invention. Indeed, embodiments of the systems for spinal adjustment (including spinal adjustment implants) disclosed herein may have one driving system (e.g., lead screws and permanent magnet, etc.), or more than one driving system. The systems for spinal adjustment disclosed herein may be attached to two vertebrae, to three vertebrae, to four vertebrae, to five vertebrae, to six vertebrae or even more vertebrae, as needed. Regardless, of the number of vertebrae to which the system for spinal adjustment is attached, the device may be a single device, attached to the vertebrae at various points (e.g., the systems shown in  FIGS.  1 - 3  and/or  10 - 12   )—of course, the device may have one or more than one complete drive system. Alternatively, the system for spinal adjustment may be modular, so that multiple (e.g., more than one), smaller devices may be connected to the desired vertebrae (e.g., the system shown in  FIG.  20   )—these devices will generally, but not always, have their own, unique drive systems (e.g., one drive system per modular portion). As will be readily apparent, because the extension member&#39;s attachment rings (having the set screw) may be moved up and down the rods and or the housing, the vertebrae to which the extension members are attached may be adjacent, separated by one or more vertebrae, or a combination of the two. 
     Besides degenerative disc disease, degenerative deformity patients (adult scoliosis, complex spine) may also be treated with spinal adjustment implants as disclosed herein. Embodiments of the spinal adjustment implants disclosed herein may be used for initial fusion surgery, or in revision surgeries. Embodiments of the spinal adjustment implants disclosed herein may be used to instrument only particular levels of the lumbar vertebrae or vertebrae of other sections of the spine. Embodiments of the spinal adjustment implants disclosed herein may be implanted using minimally invasive surgery (MIS) techniques, for example, using medial placement through a mid-line incision or by placement through small incisions using endoscopes or even operating microscopes. 
       FIGS.  13 - 16    illustrate embodiments of alternate sources to the cylindrical, radially-poled permanent magnet  516  as the driving member  514  of a spinal adjustment implant  500 ,  700 ,  800 .  FIG.  13    illustrates a non-invasively adjustable system  1300  comprising an implant  1306  having a first implant portion  1302  and a second implant portion  1304 , the second implant portion  1304  non-invasively displaceable with relation to the first implant portion  1302 . The first implant portion  1302  is secured to a first bone portion  197  and the second implant portion  1304  is secured to a second bone portion  199  within a patient  191 . A motor  1308  is operable to cause the first implant portion  1302  and the second implant portion  1304  to displace relative to one another. An external remote controller (ERC)  1310  has a control panel  1312  for input by an operator, a display  1314  and a transmitter  1316 . The transmitter  1316  sends a control signal  1318  through the skin  195  of the patient  191  to an implanted receiver  1320 . Implanted receiver  1320  communicates with the motor  1308  via a conductor  1322 . The motor  1308  may be powered by an implantable battery, or may be powered or charged by inductive coupling. 
       FIG.  14    illustrates a non-invasively adjustable system  1400  comprising an implant  1406  having a first implant portion  1402  and a second implant portion  1404 , the second implant portion  1404  non-invasively displaceable with relation to the first implant portion  1402 . The first implant portion  1402  is secured to a first bone portion  197  and the second implant portion  1404  is secured to a second bone portion  199  within a patient  191 . An ultrasonic motor  1408  is operable to cause the first implant portion  1402  and the second implant portion  1404  to displace relative to one another. An external remote controller (ERC)  1410  has a control panel  1412  for input by an operator, a display  1414  and an ultrasonic transducer  1416 , which is coupled to the skin  195  of the patient  191 . The ultrasonic transducer  1416  produces ultrasonic waves  1418  which pass through the skin  195  of the patient  191  and operate the ultrasonic motor  1408 . 
       FIG.  15    illustrates a non-invasively adjustable system  1700  comprising an implant  1706  having a first implant portion  1702  and a second implant portion  1704 , the second implant portion  1704  non-invasively displaceable with relation to the first implant portion  1702 . The first implant portion  1702  is secured to a first bone portion  197  and the second implant portion  1704  is secured to a second bone portion  199  within a patient  191 . A shape memory actuator  1708  is operable to cause the first implant portion  1702  and the second implant portion  1704  to displace relative to one another. An external remote controller (ERC)  1710  has a control panel  1712  for input by an operator, a display  1714  and a transmitter  1716 . The transmitter  1716  sends a control signal  1718  through the skin  195  of the patient  191  to an implanted receiver  1720 . Implanted receiver  1720  communicates with the shape memory actuator  1708  via a conductor  1722 . The shape memory actuator  1708  may be powered by an implantable battery, or may be powered or charged by inductive coupling. 
       FIG.  16    illustrates a non-invasively adjustable system  1800  comprising an implant  1806  having a first implant portion  1802  and a second implant portion  1804 , the second implant portion  1804  non-invasively displaceable with relation to the first implant portion  1802 . The first implant portion  1802  is secured to a first bone portion  197  and the second implant portion  1804  is secured to a second bone portion  199  within a patient  191 . A hydraulic pump  1808  is operable to cause the first implant portion  1802  and the second implant portion  1804  to displace relative to one another. An external remote controller (ERC)  1810  has a control panel  1812  for input by an operator, a display  1814  and a transmitter  1816 . The transmitter  1816  sends a control signal  1818  through the skin  195  of the patient  191  to an implanted receiver  1820 . Implanted receiver  1820  communicates with the hydraulic pump  1808  via a conductor  1822 . The hydraulic pump  1808  may be powered by an implantable battery, or may be powered or charged by inductive coupling. The hydraulic pump  1808  may alternatively be replaced by a pneumatic pump. 
     Though not illustrated, another driving element  242  may include a magneto restrictive element. A number of materials may be used to produce the components like the housing, first distraction rod, second distraction rod, first lead screw, and second lead screw, including but not limited to titanium, titanium alloys, titanium 6-4, cobalt-chromium alloys, and stainless steel. The threads on the lead screw in some embodiments may comprise Acme threads, square threads or buttress threads. A number of other possible driving systems are discussed in some detail below. 
       FIGS.  17 - 18    illustrate an implant system  1000  comprising a spinal adjustment implant  1002 , first pedicle screw  1004  and second pedicle screw  1006 . The spinal adjustment implant  1002  includes a housing  1008 , which may comprise a first housing portion  1010  and a second housing portion  1012 , joined together at a joint  1014  (e.g., similar to the joint described with respect to  FIG.  6 B ). The joint may be a weld joint, adhesive joint, threaded joint, or other type of joint. Alternatively, the housing  1008  may be constructed of a single, monolithic structure, as described in U.S. Pat. No. 9,179,938, which is incorporated by reference herein in its entirety. In certain embodiments, the housing  1008  is coupled at a first end  1016  to a base  1018  having a rod  1020 . In some embodiments, housing  1008  is fixedly coupled to the base  1018 . In other embodiments, as will be discussed below, the housing  1008  is movably couple to the base  1018 , so as to, for example, allow pivoting movement or to allow further distraction/retraction capability (through the addition of another drive system, or the incorporation of another drive member into the currently present drive system). While certain features of the rod  1020  are described below, it should be understood that any modification of this general structure is contemplated by this disclosure. 
     The rod  1020  may extend in a generally parallel direction to the housing  1008 , and be offset from the housing by a distance D. Alternatively, the rod  1020  may extend directly along the longitudinal axis of the housing. The rod  1020  is shown as extending alongside the housing on the same side as the rod  1040 . In some embodiments, the rod  1020  and the rod  1040  are not aligned with each other. In some embodiments, the rod  1020  and the rod  1040  are offset by an angle in the range of about 1-180 degrees, about 5-160 degrees, about 10-140 degrees, about 15-120 degrees, about 20-100 degrees, about 25-80 degrees, and about 30-60 degrees or any other degree of offset that may be advantageous—it will be understood that such an offset may be advantageous for applications related to the spine, or applications related to other portions of the skeletal system. The rod  1020  is configured for securement to the second pedicle screw  1006 , having a threaded shank  1022  a head  1024  and a tightening nut  1026 . While a pedicle screw is described, one of ordinary skill in the art will readily understand that any of a number of systems may be used to fix the rod  1020  to the body of a patient, for example the skeletal system (e.g., a ring and extension member-based system, such as disclosed elsewhere herein). 
     A rod  1028  (which may share one or more characteristics with rod  1020 , just described) is configured to be telescopically moveably into and out of (e.g., moveable/translatable relative/with respect to) an interior  1030  of the housing  1008  at a second end  1036  thereof. The rod  1028  may include one or more longitudinal grooves  1032  which may be engaged by an insert  1034  within the housing  1008 , thus allowing longitudinal displacement between the housing  1008  and the rod  1028 , but stopping any significant rotation between the housing  1008  and the rod  1028  (this anti-rotation member may function substantially the same as was described above with respect to other embodiments). The rod  1028  may be coupled to a base  1038  having a rod  1040 , which may extend in a generally parallel direction to the housing  1008  and/or the rod  1028 . The base  1038  may be coupled to the rod  1028  by welding, or by a screw  1029 . Alternatively, the base  1038  is pivotably coupled to the rod  1028  so that some rotational movement is allowed between the two at the connection of the two (other types of pivotable/moveable joints are contemplated, such as those that allow unidirectional motion, and/or those that allow movement in more than a single plane (i.e., rotational movement only)). In other embodiments, as will be discussed below, the rod  1028  is movably couple to the base  1038 , so as to, for example, allow pivoting movement or to allow further distraction/retraction capability (through the addition of another drive system, or the incorporation of another drive member into the currently present drive system). 
     The rod  1040  may be configured for securement to the first pedicle screw  1004 , which may include similar components as the second pedicle screw  1006 . In use, the first pedicle screw  1004  is engaged into a first vertebra, and the second pedicle screw is engaged into a second vertebra. While a pedicle screw is described, one of ordinary skill in the art will readily understand that any of a number of systems may be used to fix the rod  1040  to the body of a patient, for example the skeletal system (e.g., a ring and extension member-based system, such as disclosed elsewhere herein). In some cases, the first and second vertebrae may be adjacent each other. In other cases, the first and second vertebrae may have one or more intervening vertebrae. 
     The spinal adjustment implant  1002  is configured to be non-invasively shortened or lengthened, in order to move a first and second vertebra with respect to each other. A magnet  1042  (for example, a radially poled, cylindrical magnet) may held within a casing  1046  which is rotatably held within the housing  1008  by a radial bearing  1044 . A pin  1048  at one end of the casing  1046  may be insertable within (e.g., held by) an inner bore  1050  of the radial bearing  1044 . One or more planetary gear modules  1052 ,  1054  (such as those discussed above), may couple the magnet  1042  and casing  1046  to a lead screw (e.g., drive member, drive shaft, drive element, etc.)  1056 . A thrust bearing  1058  may be secured within the housing  1008  to protect the planetary gear modules (or stages)  1052 ,  1054  and the magnet  1042  from axial compressive (and/or tensile) stresses. 
     The lead screw  1056  may be coupled to the gear modules  1052 ,  1054  or the magnet  1042  (of course, it will be understood that gearing increases the possible torque of the system and therefore the possible force that can be generated by the system). In some embodiments, the lead screw is connected to the gear modules or the magnet using a coupler  1057  that allows some amount of axial play (as discussed above), such as by a pin  1060 . The rod  1028  may have a hollow interior  1062 , which may contain threads. In some embodiments, the hollow inter  1062  itself is threaded. Alternatively, the hollow interior  1062  may contain a nut  1064  having a female thread  1066  (e.g., the nut may be fixedly bonded to the inner surface of the hollow interior  1062 ). The external threads of the lead screw  1056  engage the female thread  1066  of the nut  1064 , thus allowing movement of the rod  1028  and the housing  1008  towards each other or away from each other, depending on the direction that the lead screw  1056  is turned. The pieces of the system  1000  may be sealed in any of a number of ways to keep out bodily fluids and to keep in any fluids contained by the device (e.g., lubricants or other fluids). Any of the seals discussed elsewhere herein may be used here as well. For example, an o-ring  1068  may be held within a circumferentially extending groove  1070  in the rod  1028  to provide a dynamic seal against an inner surface  1072  of the housing  1008  (of course, the groove may be in the inner surface of the housing as opposed to the outer surface of the rod). A moving magnetic field, for example, applied non-invasively by the External Remote Controlled (ERC)  180  of  FIGS.  4 - 5   , may be used in a patient (including but not limited to a conscious patient) to change the length of the spinal adjustment implant  1002 , thus changing the distance and/or angle between the first vertebrae and the second vertebrae, 
     Implant system  1000  has been described as having an axially asymmetric drive system. That is to say that, by contrast to the device shown in  FIG.  6 B , the implant system  1000  has a drive shaft on only one side of the spinning magnet. This means that only one end of the implant system  1000  may extend or retract from within the housing. In some embodiments, that is sufficient. 
     However, in other embodiments, the housing contains a bilaterally symmetrical drive system, including, for example, one magnet, two gear systems, and two drive shafts (as will be easily understood in view of the disclosure presented herein). 
       FIG.  19    illustrates a cross-sectional view of the system  1000  shown in  FIG.  18   , but rotated approximately 90 degrees clockwise.  FIG.  20    illustrates two systems, such as the system  1000  of  FIGS.  18 - 19    attached to the spinal column in a modular fashion at a joint (which may also be attached to the spinal column). The two devices are secured to the spinal column in series, with a shared base between them. The telescopic rods of each of the implants are secured to the shared base. 
       FIGS.  21 A- 21 D  and  FIGS.  22 A- 22 E  illustrate an embodiment of the spinal adjustment implant  2100  for implantation along the spinal system of a subject. The spinal adjustment implant  2100  is similar to the implant  700  of  FIG.  9    as it provides pivotable interfaces that may allow a potentially greater increase in the lordotic Cobb angle during compression than that permitted by the spinal adjustment implant  500   a  of  FIG.  8   . As will be discussed in more detail below, the driving member of the spinal adjustment implant  2100  can be rotated to generate a compression force that allows a first attached vertebra to rotate with respect to a second attached vertebra. 
     In some embodiments, the spinal adjustment implant  2100  comprises a driving member that is rotatably coupled to a plurality of gears. In some embodiments, the plurality of gears is coupled to a linkage system that can be coupled to a plurality of vertebra. As the driving member is rotated, the plurality of gears translates the rotational motion to cause the linkage system to pivot about center of rotation which can cause one of the attached vertebrae to rotate about the center of rotation. 
       FIGS.  21 A- 22 E  generally illustrate an embodiment which may use a motor or magnet or alternative non-invasively operable drive system to turn a worm (labeled as “worm gear” in provisional) which is engaged to a worm wheel, which moves a link in order to change the distance and/or angle between two rods (red and green) to which pedicle screws may be secured.  FIG.  21 A  illustrates an embodiment of the spinal adjustment implant  2100 . In some examples, the spinal adjustment implant  2100  can further include a housing system (not pictured) that can be disposed about the surface of the spinal adjustment implant  2100 . The spinal adjustment implant  2100  can include a driving member  2114  having a first end  2106  and a second end  2104 . The driving member  2114  may comprise any non-invasively rotatable element, such as a magnet. 
     In some embodiments, the driving member  2114  can be disposed about a first rod  2170  that extends from the first end  2106  and is rotationally coupled to a gear system  2120 . In some embodiments, the gear system  2120  can be a planetary or a harmonic drive. As the driving member  2114  is rotated, the rotation is translated to the gear system  2120 . In some embodiments the gear system  2120  can provide a high gear reduction ratio in a limited space. As the driving member  2114  rotates, the rotation causes the gear system  2120  to rotate. 
     As illustrated in  FIG.  21 A , the gear system  2120  can be coupled to a second rod  2136  that is coupled to a worm drive  2130 .  FIG.  21 C  provides a side view of the worm drive  2130 . In some embodiments, the worm drive  2130  includes a worm screw  2132  and a worm wheel  2134 . The worm drive  2130  can provide large gear reductions. As well, in some embodiments, the worm drive  2130  can provide a locking feature which can act as a brake to ensure that the worm wheel  2134  does not unintentionally cause the worm screw  2132 . As illustrated in  FIG.  21 C , in some embodiments, the worm screw  2132  is disposed about the second rod  2136  and is threaded to engage with the worm wheel  2134 . As discussed above, as the driving member  2114  is rotated, the rotation is translated to the gear system  2120  through the first rod  2170 . The gear system  2120  can then cause the rotation of the worm drive  2130  which engages with the worm wheel  2134 . 
     In some embodiments, the worm drive  2130  may engage a linkage system  2105  which can cause the rotation of an attached vertebra.  FIGS.  21 B- 21 C  illustrate two side views of the spinal adjustment implant  2100  engaged with the linkage system  2105 . In some embodiments, the linkage system can include a driven link  2140 , a coupler link  2150 , and a ground link  2160 . In some examples, the worm wheel  2134  of the worm drive  2130  has an extended portion (not illustrated) that engages with a portion of the driven link such that rotation of the worm wheel  2134  can cause rotation of the driven link  2140 . As will be discussed below, the driven link  2140  can be movably coupled with the coupler link  2150  to cause a portion of the coupler link  2150  to pivot in a first direction as the driver link  2140  rotates. The coupler link  2150  can be further secured to a ground link  2160  which allows a first attached vertebra to rotate with respect to a second attached vertebra. 
     In some embodiments, the driven link  2140  can be movably coupled to the coupler link  2150  through the engagement portion  2142  of the driven link  2140 . The engagement portion  2142  of the driven link  2140  can be disposed about the protrusion  2151  of the coupler link  2150 . A first end of the protrusion  2151  of the coupler link  2150  can be seen in  FIG.  21 C  with the driven link  2140  disposed about it. As will be discussed in more detail below, as the driven link  2140  is rotated, this can cause a portion of the coupler link to pivot. 
     The coupler link  2150  can comprise a plurality of components. As illustrated in  FIG.  21 A- 21 B , in some embodiments, the coupler link  2150  can include a first body  2152 , a second body  2143 , and a coupler rod  2156 . As discussed above, a first end of the first body  2152  of the coupler link  2150  can include a protrusion  2151  that is disposed within an engagement portion of the driven link  2140  and is movably coupled such that rotation of the driven link  2140  can cause the first body  2152  of the coupler link  2150  to pivot. The second end of the first body  2152  of the coupler link  2150  can be movably engaged with the second body  2158  of the coupler link  2150 . A coupler rod  2156  can extend from the surface of the second body  2158  to engage with a first vertebra. In some embodiments, as illustrated in  FIG.  21 A , the coupler rod  2156  can have a base portion  2154  that is movably coupled with the second body  2158 . The base portion  2154  can be circular and disposed within an opening in the second body  2158 . The second body  2158  of the coupler link  2150  can further include a protrusion  2153  that is movably coupled with the ground link  2160  at the engagement portion  2166 . A first end of the protrusion  2153  of the ground link  2160  can be seen in  FIG.  21 C  with the ground link  2160  disposed about it. As will be discussed in more detail below, the movable connection between the ground link  2160  and the second body  2158  of the coupler link  2150  can cause the second body  2158  to rotate about the engagement portion  2166 . 
     The ground link  2160  can anchor the spinal adjustment implant  2100  to a second vertebra to provide for the rotation of the first vertebra attached to the coupler rod  2156  of the coupler link  2150 . In some embodiments, the ground link  2160  can include a body  2162 , a joint portion  2168 , and a ground rod  2164 . As illustrated in  FIGS.  21 A- 21 B , the body  2162  of the ground link  2160  can include a first end that includes an engagement portion  2166  that is movably engaged with the joint portion  2168 , and a portion of the second body  2158  of the coupler link  2150 . The body  2162  of the ground link  2160  can further include the ground rod  2164  that extends from a surface of the body  2162  at the second end. In some embodiments, the ground rod  2164  can extend from the surface of the second body  2158  to engage with a second vertebra. In some embodiments, the ground rod  2164  is anchored to the second vertebra to secure the spinal adjustment implant  2100  as the first vertebra is rotated. 
       FIG.  21 D  illustrates the center of rotation  2180  of the spinal adjustment implant  2100 . As discussed above, the rotational movement of the driving member  2114  is translated to a rotation of the driven link through the gear system  2120  and the worm drive  2130 . As the driven link  2140  is rotated in a first direction, this can cause the first body  2152  of the coupler link  2150  to pivot in a first direction. This pivoting motion is translated to the second body  2158  of the coupler link  2150  and the attached first vertebra attached to the coupler rod  2156 . As mentioned above, the body  2162  of the ground link  2160  is secured to a second vertebra. The second body  2158  is movably attached to a first end of the body  2162  of the ground link  2160  such that the second body  2158  can rotate about the engagement portion  2166  of the body  2162 , causing the first vertebra to rotate in a first direction relative to the second vertebra. 
       FIGS.  22 A- 22 E  illustrates an example of the rotation of a first vertebra as a result of the rotation of the driving member  2114 .  FIG.  22 A  illustrates the spinal adjustment implant  2100  secured to a first vertebra  2191  and a second vertebra  2192  using a plurality of attachment systems  2193 ,  2194 . In some embodiments, the attachment systems can include one or more of: a pedicle screw, hook, or a wire. As shown in  FIG.  22 A , the coupler rod  2156  is secured to the first vertebra  2191  using the attachment system  2193  and the ground rod  2164  is secured to the second vertebra  2192  using the attachment system  2194 . 
       FIGS.  22 B- 22 C  illustrate the position of the first vertebra  2191  and second vertebra  2192  as the driving member  2114  is rotated.  FIG.  22 B  illustrates the position of the first vertebra  2191  before the driving member  2114  is rotated. As can be seen, a distance exists between the first vertebra  2191  and the second vertebra  2192 .  FIG.  22 C  illustrates the position of the first vertebra  2191  after the driving member  2114  is rotated. As illustrated, the first vertebra  2191  is rotated such that it is in close proximity with the second vertebra.  FIGS.  22 D- 22 E  illustrate a close up view of the linkage system of the spinal adjustment implant  2100  before and after the driving member  2114  is rotated. As seen in  FIG.  22 E , the rotation of the driving member  2114  rotates the worm drive  2130  such that the driven link  2140  pivots in a first direction and the coupler link  2150  rotates in a first direction about the center of rotation  2180 . The rotation of the coupler link  2150  rotates the attached first vertebra  2191  such that the distance between the first vertebra  2191  and the second vertebra  2192  is reduced. 
       FIGS.  23 A- 23 C  generally illustrate an embodiment using differential gearing, including one or more sun gears and planetary gears, to increase the amount of force that can be placed on the vertebrae during adjustment (e.g., compression) via relatively high gear ratios. The compact packaging of the gears increases the efficiency of the torque, and thus force, that can be delivered within a small profile implant.  FIGS.  23 A-C  illustrate a spinal adjustment implant  2300  for implantation along the spinal system of a subject. In some cases, the subject may be a patient having degenerative disc disease that necessitates fusion of some or all of the lumbar vertebrae through fusion surgery. The spinal implant  2300  is configured to be used in place of traditional rods, which are used to maintain posterior decompression and stabilize during fusion surgery. Some embodiments of the spinal implant  2300  are compatible with interbody spacers placed between the vertebrae being treated. The spinal adjustment implant  2300  may comprise a housing  2302  which includes a first end and a second end. The housing  2302  includes a cavity  2304  which may be substantially similar to the cavities described in other embodiments disclosed herein. The cavity  2304  may include elements configured to maintain certain elements of the assembly within the housing  2304 , for example, protrusions, grooves, or abutments. The housing  2302  may be made from materials which are biocompatible and which may allow for relatively small wall thicknesses while maintaining the structural integrity of the housing  2302  when in use. For example, the housing  2302  may comprise titanium alloys, ceramics and/or biocompatible polymers. Various sizes and shape of the housing  2302  are expressly contemplated, although preferably the housing  2302  is sized to be implanted within the body of a patient. For example, in the embodiments illustrated in  FIGS.  23 A-C  the housing  2302  comprises a cylindrical shape, can have an outer diameter of about 10 mm, and can have a length of about 45 mm. In some embodiments the housing  2302  may be from about 20 mm to about 70 mm long, from about 30 mm to about 60 mm long, or from about 40 mm to about 50 mm long. In some embodiments the housing  2302  may have a diameter from about 5 mm to about 20 mm, from about 7 mm to about 15 mm, or from about 9 mm to about 11 mm. 
     A driving member  2306  is rotatably disposed within the cavity  2304  of the housing  2302 . The driving member  2306  may comprise any non-invasively rotatable element, for example a rotatable element that is substantially similar to rotatable elements described in other embodiments disclosed herein. The particular embodiment of the driving member  2306  illustrated in  FIGS.  23 A-C  comprises a cylindrical, radially-poled permanent magnet  2308  that is secured within the cavity  2304 . The magnet  2308  is disposed in the cavity  2304  such that the magnet  2308  is free to rotate about a central axis  2310  within the cavity  2304 . The magnet may be secured within the cavity by means substantially similar to those means described in other embodiments disclosed herein. It is contemplated that the magnet  2308  may comprise a variety of shapes and sizes. In the embodiment illustrated in  FIGS.  23 A-C  the magnet comprises a cylindrical shape. The magnet  2308  is sized to fit within the cavity  2304 . In some embodiments the magnet  2308  may be about 9.5 mm in diameter and about 21 mm long. In some embodiments the magnet  2308  may have a diameter from about 5 mm to about 20 mm, from about 7 mm to about 15 mm, or from about 9 mm to about 11 mm. In some embodiments the magnet  2308  may be from about 10 mm to 30 mm long, from about 15 mm to about 25 mm long, or from about 17.5 mm to about 22.5 mm long. 
     The spinal adjustment implant  2300  can include at least a first rotatable driver  2312  which includes a hole that comprises a female threaded portion  2314 . In the embodiment illustrated in  FIGS.  23 A-C  the driving member  2306  includes a first driver  2312  and a second driver  2316 . The second driver  2316  can be substantially identical to the first driver  2312  and can include a hole that comprises a female threaded portion  2318 . In some embodiments the first and second drivers  2312 ,  2316  can be coupled to the driving member  2306  by means substantially similar to those described in embodiments disclosed herein. In some embodiments a first rod  2320  has a first end comprising a male threaded portion  2322  and a second end  2324  configured to be coupled to a portion of the skeletal system. In some embodiments the second end  2324  of the first rod  2320  is configured to be coupled to a first portion of the spinal system via means substantially similar to those described in embodiments disclosed herein. The first portion of the spinal system may be a first vertebra. For example, the second end  2324  of the first rod  2320  may be coupled to the first vertebra by a first extension member  2326 , or directly via one or more of: a pedicle screw; hook; wire; or other attachment system. The first extension member  2326  may be substantially similar to an extension member described in other embodiments disclosed herein. The first extension member  2326  may extend generally transversely in relation to the housing  2302  and/or first rod  2320 . The first extension member  2326  may be coupled to a first vertebra directly, via one or more of: a pedicle screw; hook; wire; or other attachment system. In some embodiments, for example the embodiment illustrated in  FIGS.  23 A- 23 B , a second rod  2328  may be substantially similar to the first rod  2320 . The second rod  2328  may comprise a first end comprising a male threaded portion  2330  and a second end  2332  configured to be coupled to a portion of the skeletal system, for example a second vertebra. The second rod  2328  may be secured to the second vertebra by a second extension member  2334 . The second extension member  2334  may be coupled to the second vertebra directly, via one or more of: a pedicle screw; hook; wire; or other attachment system. 
     Referring to  FIG.  23 B , the female threaded portion  2314  of the first driver  2312  and the male threaded portion  2322  of the first rod  2320  threadingly engage each other such that rotation of the first driver  2312  causes the first rod  2320  to move along a first longitudinal axis  2336  ( FIG.  23 A ) in a first longitudinal direction  2338 . The female threaded portion  2318  of the second driver  2316  and the male threaded portion  2330  of the second rod  2328  threadingly engage each other such that rotation of the second driver  2316  causes the second rod  2328  to move along a second longitudinal axis  2340  ( FIG.  23 A ) in a second longitudinal direction  2342 . Although the drivers  2312 ,  2316  are described as comprising female threaded portions  2314 ,  2318  which engage with male threaded portions  2322 ,  2330  of the rods, in some embodiments the drivers  2312 ,  2316  may comprise male threaded portions and the rods may comprise corresponding female threaded portions. 
     The spinal adjustment implant  2300  may additionally comprise a gear module or modules which can be placed between the driving member  2306  and one or both of the first and second threaded drivers  2312 ,  2316 . In some embodiments one or both of the threaded drivers  2312 ,  2316  may comprise a gear including a plurality of teeth positioned around an outer edge of the driver and configured to engage with the gear modules. For example, each of the first and second drivers  2312 ,  2316  may comprise 32 teeth. In some embodiments the drivers  2312 ,  2316  may each comprise from 20 to 40 teeth, from 10 to 80 teeth, or more than 80 teeth. As shown in  FIGS.  23 A- 23 C , the first driver  2312  comprises 32 teeth which are configured to engage with the first gear module  2344 . The gear module  2344  may comprise a gear train which can provide a high gear reduction between the driving member  2306  and the first driver  2312 . A high gear reduction, or step-down, allows for a relatively small torque generated by the driving member  2306  to be amplified, thereby allowing the first driver  2312  to apply high force to the first rod  2320 . For example, in some embodiments the gear reduction between the driving member  2306  and the drivers  2312 ,  2316  may be about 4:1. In some embodiments the gear reduction ratio may be greater than 1:1, for example 2:1, 4:1, 8:1, 16:1 or more. The gear module or modules can comprise planetary gearing, including sun gears, ring gears and planet gears. In some embodiments the gear module may comprise differential gears. The differential gears may include, for example, bevel gears, spur gears, worm gears, and/or a Torsen-type differential. 
     Referring to  FIGS.  23 B- 23 C , the first gear module  2344  may comprise a first grouping of gears  2346 ,  2348  which are positioned at a first end of the rotatable element, for example the magnet  2308  of the driving member  2306 . Although the embodiment illustrated in  FIGS.  23 A- 23 C  includes two gears  2346 ,  2348  positioned at the first end of the magnet  2308 , it is expressly contemplated that the first grouping of gears may comprise more or fewer gears, for example, one gear, three gears, four gears, five gears, or more. The gears  2346 ,  2348  of the first grouping of gears are radially arranged around the central axis  2310  of the magnet  2308 . The gears  2346 ,  2348  may comprise, for example, ten teeth. In some embodiments the gears  2346 ,  2358  may comprise more or fewer teeth, for example, from five to thirty, from seven to twenty, or from ten to fifteen teeth. The gears  2346 ,  2348  engage with a second grouping of gears  2350 ,  2352 , which are positioned at the first end of the magnet  2308 , and are radially arranged around the central axis  2310  of the magnet  2308  adjacent to gears  2346 ,  2348 , respectively. The gears  2350 ,  2352  may have a height greater than the height of the gears  2346 ,  2348  such that the gears  2350 ,  2352  extend outwardly past the gears  2346 ,  2348  along the direction of the central axis  2310 . The gears  2350 ,  2352  of the second grouping may have the same, or about the same number of teeth as the gears  2346 ,  2348  of the first grouping, for example ten teeth. Likewise, the second grouping may comprise a number of gears corresponding to the number of gears in the first grouping, for example the second grouping may comprise the same number of gears as the first grouping. 
     The gears  2350 ,  2352  of the second grouping may act as planetary gears and can engage with a first sun gear  2354  positioned at a first end of the magnet  2308  such that the central axis of the sun gear  2354  is aligned with the central axis  2310  of the rotatable element, for example the magnet  2308 , of the driving member  2306 . The sun gear  2354  comprises a greater number of teeth than each of the gears  2350 ,  2352  so as to provide a gear reduction and amplify the torque generated by the rotatable element of the driving member  2306 . For example, the sun gear  2354  may comprise sixteen teeth. In some embodiments the sun gear may comprise from fifteen to thirty teeth, from thirty to fifty teeth, from fifty to one hundred teeth, or more than one hundred teeth. The sun gear  2354  additionally engages with a first intermediate gear  2356  that comprises a greater number of teeth than the sun gear  2354  so as so provide a gear reduction and amplify the input torque from the sun gear  2354 . The first intermediate gear  2356  may comprise a number of teeth corresponding to the number of teeth of the sun gear  2352 , for example twice as many teeth, four times as many teeth, eight times as many teeth, or more. In some embodiments the first intermediate gear may comprise thirty-two teeth. 
     The first intermediate gear  2354  can be fixedly attached to the second intermediate gear  2356  such that the central axes of the gears  2354 ,  2356  are substantially aligned. One rotation of the first intermediate gear  2354  will thereby result in one rotation of the second intermediate gear  2356 . The second intermediate gear  2356  comprises fewer teeth than the first intermediate gear  2354 , for example half as many teeth, one quarter as many teeth, one eighth as many teeth or fewer. In some embodiments the second intermediate gear  2356  may comprise sixteen teeth. The second intermediate gear  2356  engages with the teeth of the first driver  2312  and provides for a gear reduction between the rotation of the rotatable element of the driving member  2306  and the first driver  2312  as described above. As described above, the first gear module  2344  therefore allows the relatively small torque generated by the driving member  2306  to be converted into a relatively high torque at the first driver  2312 , the rotation of which thereby causes the first rod  2320  to move along a first longitudinal axis  2336  ( FIG.  23 A ) in a first longitudinal direction  2338 . 
     The spinal adjustment implant  2300  may additionally comprise a second gear module  2358  which is substantially similar to the first gear module  2344  and is positioned at the second end of the rotatable element of the driving member  2306 . The second gear module  2358  can be placed between driving member  2306  and the second driver  2316  and may function in a substantially identical manner as the first gear module  2344  as described above. Additionally, in some embodiments the first and second groupings of gears of the second gears module may be attached or engaged with the corresponding gears of the first and second grouping of the first gear module  2344 . For example, the corresponding gears of the first and second groupings of the first and second gears modules may share corresponding axles. The sun gears of the first and second gear modules may not be attached or engaged with one another and the sun gear  2354  of the first gear module may rotate independently from the sun gear of the second gear module  2358 . 
     Furthermore, the threaded portions of the first and second rods  2324 ,  2328  and the threaded portions of the first and second drivers  2312 ,  2316  are configured such that rotation of the rotatable element of the driving member  2306  causes a corresponding rotation of the first and second drivers  2312 ,  2316  which thereby causes the first rod  2324  to move in a first axial direction  2328  and the second rod  2328  to move in a second axial direction  2342 . 
     As illustrated in  FIG.  23 A , the first and second gear modules  2344 ,  2358  may be positioned within a first gear module housing  2360  and a second gear module housing  2362 , respectively. The gear module housings  2360 ,  2362  can be attached to, and/or integrally formed with the housing  2302  and positioned at the first and second ends thereof. The gear module housings  2360 ,  2362  may include cavities configured to maintain the gear modules or modules therein. The cavities may include elements configured to maintain certain elements of the assembly within the housings  2360 ,  2362 , for example, protrusions, grooves, or abutments. The housings  2360 ,  2362  may be made from materials which are biocompatible and which may allow for relatively small wall thicknesses while maintaining the structural integrity of the housings  2360 ,  2362  when in use. For example, the housings  2360 ,  2362  may comprise the same or similar materials as the housing  2302 . 
     The spinal adjustment implant  2300  may further comprise a retainer  2364  which is configured to receive the threaded portions  2322 ,  2330  of the first and second rods  2320 ,  2328 . The retainer can take the form of, for example, a hollow tube, with the threaded portions  2322 ,  2330  of the rods disposed therein. The retainer  2364  can be secured to a portion of the skeletal system, for example a third vertebra, preferably positioned between the first and second vertebra. The retainer  2364  can be secured to the third vertebra directly, by a third extension member  2366 , and/or in a manner similar to the manner in which the first rod  2320  is secured to the first vertebra as described above. The third extension member  2366  may be coupled to the third vertebra directly, via one or more of: a pedicle screw; hook; wire; or other attachment system. The retainer  2364  can be attached to, and/or integrally formed with the gear module housings  2360 ,  2362  at the respective ends of the retainer  2364 . In this manner the retainer  2364 , which is secured to a portion of the skeletal system, may provide support for, and secure, the housing  2302  via the gear module housings  2360 ,  2362 , within the body of the patient. A central axis of the retainer  2364  may be substantially parallel to a central axis of the driving member driving member  2306 , with an offset therefrom. In some embodiments the offset between the central axis of the retainer  2364  and the central axis of the housing  2302  and/or driving member  2306  may be about 12 mm. In some embodiments the offset may be from about 4 to about 16 mm, greater than 16 mm, or greater than 32 mm or greater. 
       FIGS.  24 A- 24 D  generally illustrate an embodiment wherein a motor or magnet, etc. drives a worm that engages and turns a worm gear which may be rotationally coupled (e.g., in serial) with a pinion that drives a rack.  FIGS.  24 A-D  illustrate another embodiment of the spinal adjustment implant  2400 . The spinal adjustment implant  2400  includes a drive member  2402 , a first rod  2404 , a second rod  2406 , a first securement portion  2408 , a second securement portion  2410 , and a third securement portion  2412 . 
     As illustrated in  FIG.  24 A- 24 B , the driving member can include a first end that is attached to a worm screw  2416  of a worm drive  2414 . As the drive member  2402  rotates, the worm screw  2416  of the worm drive  2414  is rotated. The worm screw  2416  is configured to engage the worm wheel  2418  of the worm drive  2414  and translates the rotational energy of the drive member  2402  and worm screw  2416  in a first direction to a rotation in a second direction. In some embodiments, the driving member can be a magnet. The magnet may be 9 mm in diameter and 25 mm long. The drive member  2402  and the worm drive  2414  can be covered in a flexible membrane or below covering assembly that can be configured to protect the teeth of the worm drive  2414  from body materials. In some embodiments, this housing  2420  can be 10 mm in diameter, 38 mm long, and 10 mm in offset. 
     In some embodiments, the first rod  2404  and the second rod  2406  can include a tooth portion that is configured to engage the teeth of the worm wheel  2418 . The first rod  2404  and second rod  2406  can include an external housing  2422  that can secure the position of the first rod  2404  and second rod  2406  about the worm wheel  2418 . As illustrated in  FIG.  24 C , one end of the first rod  2404  is located above one end of the second rod  2406 . In some embodiments, the first rod  2404  has a first engagement portion  2424  that includes a plurality of teeth that is configured to engage the teeth of the worm wheel  2418  above the second rod  2406 . In some embodiments, the second rod  2406  has a second engagement portion  2426  that includes a plurality of teeth that is configured to engage the teeth of the worm wheel  2418  below the first rod  2404 . 
       FIG.  24 C  illustrates the movement of the first rod  2404  and the second rod  2406  as the worm wheel  2418  of the worm drive  2414  is rotated. As shown by the arrows in  FIG.  24 C , as the worm wheel  2418  rotates in a first direction, it causes the first engagement portion  2424  of the first rod  2404  and the second engagement portion  2426  of the second rod  2406  to engage with the teeth and to move past each other. As the first rod  2404  and the second rod  2406  move past each other, the first rod  2404  pivots downward near the engagement portion to cause the opposite end of the first rod  2404  to tilt upward. Similarly, as the worm wheel  2418  engages the second engagement portion  2426  of the second rod  2406 , the second rod  2406  pivots downward near the engagement portion to cause the opposite end of the second rod  2406  to tilt upward. In some embodiments, this compression near the worm wheel  2418  can occur simultaneously in both the first rod  2404  and the second rod  2406  as shown. The compression does not need to be purely linear as there is a rotational degree of freedom. In some embodiments, the first rod  2404  and the second rod  2406  can be bent past each of the respective engagement portions. 
       FIG.  24 D  illustrates a cross sectional view of the spinal adjustment implant  2400  as it is implanted into a plurality of vertebra of the spinal system. The first rod  2404  can be secured to a first vertebra  2428  of the spinal system using a first securement portion  2408 . In some embodiments, the first securement portion  2408  can be a screw. In some embodiments, the second rod  2406  can be secured to a second vertebra  2430  of the spinal system using a second securement portion  2410 . Similarly, in some embodiments, the second securement portion  2410  can be a screw. In some embodiments, a third securement portion  2412  adjacent to the second engagement portion  2426  of the second rod  2406  can be secured to a middle vertebra  2432  of the spinal system. In some embodiments, the middle vertebra  2432  can be located between the first vertebra  2428  and the second vertebra  2430 . 
     As illustrated in  FIG.  24 D , the third securement portion  2412  can be the point about which compression of the first vertebra  2428  and second vertebra  2430  occur. As seen, as the worm wheel  2418  rotates, the first engagement portion  2424  of the first rod  2404  can move past the second engagement portion  2426  of the second rod  2406 . The ends of the first rod  2404  and second rod  2406  where the respective engagement portions are located bend downward, such that either ends of the first rod  2404  and second rod  2406  bend upwards. This can create a curve in the spinal system about the middle vertebra  2432 . 
       FIGS.  25 A- 25 E  generally illustrate an embodiment including a Torsen differential which may allow a single motor or magnet output (rotation) to drive two sides of an implant at the same rate, or at different rates from each other. For example, different displacement rates or different angulation change rates.  FIGS.  25 A- 25 E  illustrate a spinal adjustment implant  2500  for implantation along the spinal system of a subject. The spinal adjustment implant  2500  is similar to the implant  700  of  FIG.  9    as it includes a first pivotable interface and a second pivotable interface that may allow a potentially greater increase in the lordotic Cobb angle during compression than that permitted by spinal adjustment implants such as the spinal adjustment implant  500  of  FIGS.  1 - 3 C . As discussed above for related implants, the spinal implant  2500  is configured to be used in place of traditional rods, which are used to main posterior decompression and stabilize during fusion. Some embodiments of the spinal implant  2500  are compatible with interbody spacers placed between the vertebrae being treated. 
     The spinal implant  2500  comprises a housing  2502  having a first end  2504  and a second end  2506 . The housing  2502  can include a plurality of portions that extend between the first end  2504  of the housing  2502  and the second end  2506  of the housing  2502 . In some embodiments, the housing  2502  can include a first extendible portion  2508 , a planet housing  2512 , a second extendible portion  2510 , and a magnet housing  2514 . 
     The planet housing  2512  can include openings at both ends and a cavity  2513  there through. As will be discussed in more detail below, the planet housing  2512  can be configured to house a plurality of gears that can translate rotational motion into a longitudinal extension or retraction through the housing  2502 . 
     In some embodiments, the planet housing  2512  is positioned longitudinally between the first extendible portion  2508  and the second extendible portion  2510 . The first extendible portion  2508  is located at the first end  2504  of the housing  2502  and the second extendible portion  2510  is located at the second end  2506  of the housing  2502 . The first extendible portion  2508  and the second extendible portion  2510  can both include a first cavity  2509  and a second cavity  2511  respectively that can house a screw. In some embodiments, the first extendible portion  2508  and the second extendible portion  2510  can include a projection portion  2516 ,  2518  that extends perpendicularly from the surface of the first extendible portion  2508  and second extendible portion  2510  respectively. A rod  2517  can be configured to extend from the projection  2516  in a first direction and a rod  2519  can be configured to extend from the projection  2518  in a second direction such that the rod  2517  and rod  2519  extend in opposite directions away from each other. As will be discussed in more detail below, in some embodiments, the first cavity  2509  and the second cavity  2511  can include an inner thread that can each threadingly engage their respective screws such that rotation of each of the screws can cause the first extendible portion  2508  and the second extendible portion  2510  to extend or retract from the planet housing  2512 . 
     The magnet housing  2514  can be located adjacent to the planet housing  2512  such that the magnet housing  2514  and the planet housing  2512  run parallel to one another. The magnet housing  2514  can include a cavity  2514  which extends between the first end  2504  and the second end  2506 . The cavity  2514  may have a variable inner diameter along its length or may have a generally constant inner diameter. The inner wall of the magnet housing  2514  may have circumferential grooves or abutments (not illustrated) that axially maintain certain elements of the assembly. A driving member  2520  can be rotatably disposed within the cavity  2515 . The driving member  2520  may comprise any non-invasively rotatable element such as those described in relation to  FIGS.  20 - 23   . In some embodiments, the driving member  2520  can be a magnet. In some embodiments, the magnet may be 9.5 mm in diameter and 41 mm long. Of course it will be understood that other dimensions may be used. In some embodiments, the planet housing  2512  and the magnet housing  2514  can include a side opening near the second end of the planet housing  2512  and magnet housing  2514  that provides an interior connection between the planet housing  2512  and the magnet housing  2514 . As will be discussed in more detail below, the interior connection can house a gear system that translates rotational movement of the driving member  2520  into longitudinal translation (e.g., extension or retraction) of the first extendible portion  2508  and the second extendible portion  2510 . 
       FIG.  2 C  illustrates an enlarged view of the second end  2506  of the spinal adjustment implant  2500  with the housing  2502  removed. In some embodiments the housing  2502  can include a driving member  2520 , a worm drive  2530 , a miter gear mesh  2540 , a first screw  2524 , a second screw  2522 , a Torsen differential  2524  that is housed in a planet carrier  2552 . 
     In some embodiments, the driving member  2520  can be disposed about a rod  2531  that extend from the second end  2506  and is rotationally coupled to a worm drive  2530 . The worm drive  2530  can include a worm screw  2532  and a worm wheel  2534 . In some embodiments, the worm gear reduction may be 20:1. As the driving member  2520  is rotated, the attached rod  2531  rotates the worm drive  2530  which causes the worm wheel  2534  to turn. 
     In some embodiments, the worm drive  2530  may engage a miter gear mesh  2540  which can translate the rotational energy of the worm drive  2530  into longitudinal movement along the length of the housing  2502 . A type of bevel gear, miter gears are useful for transmitting rotational motion at a 90 degree angle. In some embodiments, the miter gear mesh  2540  can translate rotational motion at a 90 degree angle with a 1.3:1 ratio. In some embodiments, the miter gear mesh  2540  can be replaced with any type of gear system that can translate rotational motion at an angle. The miter gear mesh  2540  can include a first gear  2542  and a second gear  2544 . In some embodiments, the first gear  2542  is attached to the worm wheel  2534 , such that rotation of the worm wheel  2534  causes rotation of the first gear  2542 . The first gear  2542  can have a plurality of teeth that can engage with the teeth of the second gear  2544 . The second gear  2544  can be disposed about a rod  2523  such that rotation of the second gear  2544  causes rotation of the rod  2523  in the same direction. 
     In some embodiments, the second gear  2544  of the miter gear mesh  2540  can be attached to a rod  2554  that engages with a Torsen differential  2550  that is located within a planetary carrier  2552 . A Torsen differential, and in similar gear systems, serves to provide a mechanical self-locking center differential which regulates the power between the front and rear axles according to demand. A Torsen differential operates on the basis of torque sending and responds to varying rotational forces between the input and output shafts. This can enable variable distribution of the driving torque between the axles. On a Torsen differential, the plurality of output gears are interconnected by worm gears. This can limit high differential rotational speeds, but still balance the speeds when cornering. As will be discussed in more detail below, the Torsen differential  2550  can provide a different rate of rotation of attached members. 
       FIG.  25 D  illustrates an enlarged view of the Torsen differential  2550  without the planetary carrier  2552 . As can be seen, the Torsen differential  2550  can engage with the rod  2554  at a second end  2506  and a portion of the first screw  2524  at a first end  2504 . In some embodiments, as illustrated in  FIG.  25 B- 25 D , rotation of the rod  2554  by miter gear mesh  2540  can cause the Torsen differential  2550  to translate the rotational energy to the first screw  2524 . 
     As discussed above, the spinal adjustment implant  2500  can be sued to non-invasively maintaining or changing the magnitude of compression between two vertebrae following fusion surgery (post-operatively) and/or non-invasively changing the magnitude of lordosis. As well, because the spinal adjustment implant  2500  includes a plurality of pivotal interfaces, the spinal adjustment implant  2500  can provide for a potentially greater increase in the lordotic Cobb angle during compression. This can be done by first rotating the driving member  2520  which causes rotation of the worm screw  2532  of the worm drive  2530 . The worm screw  2532  engages with the worm wheel  2534  of the worm drive  2530  and rotates the attached first gear  2542  of the miter gear mesh  2540 . As discussed above, the first gear  2542  of the miter gear mesh  2540  engages with the second gear  2544  of the miter gear mesh  2540  to translate the rotational energy at an angle. The rotation of the second gear  2544  rotates the attached rod  2523  and engages the Torsen differential  2550 . As discussed above, the Torsen differential  2550  can engage with a portion of the first screw  2524  to rotate the first screw  2524 . As well, the rod  2523  is attached to the second screw  2522  and rotates the screw. In some embodiments, the Torsen differential  2550  can provide the same or a different rate of rotation of the first screw  2524  and the second screw  2522 . In some embodiments, this can provide for different displacement rates between the first screw  2524  and the second screw  2522 . In some embodiments, this can produce the same or different angulation change rate between vertebrae that are attached to the spinal adjustment implant  2500 . 
     As discussed above, in some embodiments, the first extendible portion  2508  and the second extendible portion  2510  further include a first cavity  2509  and second cavity  2511  respectively. Each of the first cavity  2509  and second cavity  2511  can further include a threaded interior that can be configured to movably engage the first screw  2524  and second screw  2522  respectively. In some embodiments, the rotation in a first rotational direction of the driving member  2520  causes both the first screw  2524  and the second screw  2544  to move into the first cavity  2509  and second cavity  2511  respectively. This can cause the rod  2517  attached to the first extendible portion  2508  and the rod  2519  of the second extendible portion  2510  to move towards each other and reduce the reach of the rod  2517  and rod  2519 . This motion is capable of generating a force on the spine at the points of attachment of the spinal adjustment implant  2500  and increasing the compressive force(s) between the vertebrae. 
     Similarly, in some embodiments, the rotation in a second rotational direction of the driving member  2520  causes both the first screw  2524  and the second screw  2544  to extend out of the first cavity  2509  and second cavity  2511  respectively. The rotation in a second rotational direction can cause the first extendible portion  2508  and the second extendible portion  2510  to move in opposite directions along the same axis. This can cause the rod  2517  attached to the first extendible portion  2508  and the rod  2519  of the second extendible portion  2510  to move away from each other and increase the reach of the rod  2517  and rod  2519 . This motion is capable of generating a force on the spine at the points of attachment of the spinal adjustment implant  2500  and decreasing the compressive force(s) between the vertebrae. 
     In some embodiments, the inner threading of the first cavity  2509  and second cavity  2511  can cause the first screw  2524  and second screw  2544  to rotate to move the attached first extendible portion  2508  and second extendible portion  2510  to move in the same direction along the same axis. For example, the first extendible portion  2508  can move in a first direction along the axis, wherein the first screw  2524  extends out of the first cavity  2509  and the second extendible portion  2510  can move in a first direction as well along the axis, wherein the second screw  2544  retracts into the second cavity  2511 . The attached rod  2517  and rod  2519  thereby move in the first direction. In some embodiments, the distance between the rod  2517  and rod  2519  can maintain their distance, reduce their distance, or increase in distance. The aforementioned embodiment could apply in the reverse as well—wherein the first extendible portion  2508  and second extendible portion  2510  move in a second direction along the axis. 
       FIGS.  25 A and  25 E  illustrate the spinal adjustment implant  2500  secured to a plurality of vertebra. The spinal adjustment implant  2500  can be secured to a plurality of vertebrae that are secured using a plurality of rods. As illustrated in  FIG.  25 E , the spinal adjustment implant  2500  includes a first rod  2561  located near the first end  2504  of the housing  2502 . The first rod  2561  can be configured to couple to a first portion of the spinal system. The first portion of the spinal system may be a first vertebra  2571 . In some embodiments, the spinal adjustment implant  2500  includes a second rod  2563  located near the second end  2506  of the housing  2502 . The second rod  2563  can be configured to couple to a second portion of the spinal system. The second portion of the spinal system may be a second vertebra  2573 . In some embodiments, the spinal adjustment implant  2500  includes a middle rod  2562  located between the first end  2504  and the second end  2506  of the housing  2502 . The middle rod  2562  can be configured to couple to a third portion of the spinal system. The third portion of the spinal system may be a third vertebra  2572  located between the first vertebra  2571  and the second vertebra  2573 . As indicated, a first angle of rotation is in a clockwise direction while a second angle of rotation is in a counter-clockwise direction. As noted in  FIG.  25 A , the Torsen differential can cause the rotation about the first and second angles of rotation to occur at the same or different rates. 
     In some embodiments, the first rod  2561  and second rod  2563  can serve as a plurality of pivotable interfaces that can allow a potentially greater increase in the lordotic Cobb angle during compress. As is illustrated in  FIG.  25 E , the first rod  2561  and second rod  2563  allow the secured first vertebra  2571  and the second vertebra  2573  to pivot about the middle rod  2563  that is secured to the third vertebra  2572 . The direction of the rotation of the rods is illustrated by the curved arrows illustrated in  FIG.  25 E . In some embodiments, the first rod  2561  and second rod  2563  are non-invasively lockable and nonlockable. In some embodiments, the first and second rods  2561 ,  2563  are configured to be non-invasively lockable and unlockable as part of the non-invasive adjustment. In some embodiments, the first and second rods  2561 ,  2563  are configured to be non-invasively lockable and unlockable in conjunction with the rotation of the driving member  2520 . 
     In some embodiments, the first and second rods  2561 ,  2563  are intermittently locked and unlocked during an adjustment procedure. 
     In some embodiments, one or more of the pivotable interfaces is configured to rotate freely in either direction (e.g., clockwise and/or counterclockwise). In some embodiments, one or more of the pivotable interfaces is partially constrained to have free rotation in one direction but no rotation in the other direction—this may be accomplished using a free wheel or other one-way clutching. In some embodiments, the rods include two-way locking so that they may lock and unlock automatically by the operation of the spinal adjustment implant. For example, the Eternal Remote Controller (ERC) may be used to lock and unlock a magnetic lock which is capable of reversibly removing the rotational freedom of the pivotable interface(s). In some embodiments which may be either freely rotating or lockable, there may additionally be constrained rotation or motion, wherein there are limits, extents, or detents that limit the total amount of travel of a particular rotation or motion. 
       FIGS.  26 A- 26 H  generally illustrate a motor or magnet that by use of a cam is able to intermittently lock or unlock a mechanism, as it is adjusted. In some embodiments, the unlocking may temporarily allow for change in angulation, which is then locked again, after the change occurs.  FIGS.  26 A- 26 H  illustrate various views of a pivot lock mechanism  2600 , according to some embodiments. The pivot lock mechanism  2600  may be used, for example, to lock and unlock the first and second pivotable interfaces  729 ,  727  of the spinal adjustment implant  700  shown in  FIG.  9   . The pivot lock mechanism  2600  includes a motor  2602  operably coupled to a drive shaft  2608 . In some embodiments, the motor  2602  comprises a magnet that may be magnetically coupled to one or more other magnets. For example, in some embodiments, the motor  2602  may be magnetically coupled to the one or more magnets of the magnetic handpiece  178  shown in  FIGS.  4  and  5   . In some embodiments, the magnet  2602  comprises a cylindrical, radially-poled permanent magnet, although any suitable size, shape, and polarity is appreciated. The magnet may include a north pole  2618  and a south pole  2620 . As shown in  FIGS.  26 A- 26 H , the drive shaft  2608  may extend longitudinally from the motor  2602 . In some embodiments, the center longitudinal axes of the motor  2602  and the drive shaft  2608  are aligned. The motor  2602  and the drive shaft  2608  may be operably coupled such that the drive shaft  2608  rotates when the motor  2602  rotates. In some embodiments, the drive shaft  2608  and the motor  2602  rotate at the same angular velocity and/or at different angular velocities. For example, in some embodiments, the motor  2602  rotates at one, two, three, or more discreet angular velocities, and/or at any angular velocity between a minimum and maximum value. However, it should be appreciated that the motor  2602  and the drive shaft  2608  may rotate at any suitable angular velocity. In some embodiments, the motor  2602  can rotate in either direction (e.g., clockwise and/or counterclockwise). 
     The pivot lock mechanism  2600  further includes a rod  2616 , a pivot member  2614 , and a pin  2615 . In some embodiments, a first end of the rod  2616  may be attached to, for example, a pedicle screw, and a second end of the rod  2616  may be attached to the pivot member  2614 . In some embodiments, the rod  2616  can be any of the rods disclosed herein, such as the rod shown in  FIG.  48   . The pin  2615  may couple the pivot member  2614  to a pivot slide  2612 . In some embodiments, the pivot slide  2612  includes a slot  2621  configured to accommodate first and second pivot locks  2604   a ,  2604   b . The first and second pivot locks  2604   a ,  2604   b  may be constrained to vertical motion and may be independently spring loaded downward with corresponding first and second elastic members  2606   a ,  2606   b , respectively. In some embodiments, the first and second elastic members  2606   a ,  2606   b  comprise springs, such as, for example, compression springs. As the pivot member  2614  rotates, the pivot slide  2612  is configured to translate horizontally back and forth. For example, in some embodiments, the pivot slide  2612  may be able to cyclically translate in opposing first and second directions. In some embodiments, the horizontal translation of the pivot slide  2612  is perpendicular relative to the vertical motion of the first and second pivot locks  2604   a ,  2604   b . Translation of the pivot slide  2612  may cause the rod  2616  to adjust the positioning of one or more pedicle screws and/or the positioning of one or more other rods. 
     As shown in  FIGS.  26 D and  26 E , the slot  2621  has two ramps  2622 ,  2624  spaced opposite of each other. The bottom surface of the slot  2621  that extends between the two ramps  2622 ,  2624  may be flat or any other suitably shaped surface. The first and second pivot locks  2604   a ,  2604   b  may be configured to settle into ramps  2624 ,  2622 , respectively, regardless of the angle of the rod  2616 . In some embodiments, the rod  2616  is unable to force the pivot slide  2612  to move when the first and second pivot locks  2604   a ,  2604   b  are in place.  FIGS.  26 D and  26 E  illustrate two exemplary views showing the first and second pivot locks  2604   a ,  2604   b  locked in place. 
     The pivot lock mechanism  2600  also includes a cam  2610  operably coupled to the drive shaft  2608 . The cam  2610  alternately unlocks and locks the pivot member  2614  by engaging the first and second pivot locks  2604   a ,  2604   b . Rotation of the cam  2610  may alternately unlock and lock the pivot member  2614  as it is rotated. For example, in some embodiments, unlocking the pivot lock mechanism  2600  may temporarily allow for a change in angulation of the rod  2616 , after which the pivot member  2614  may be locked. 
     For example, as shown in  FIG.  26 G , the cam  2610  may intermittently unlock the pivot member  2614  by lifting the first and/or second pivot locks  2604   a ,  2604   b  upward by overcoming the downward force exerted by the first and/or second elastic members  2606   a ,  2606   b , respectively. In some embodiments, when the pivot member  2614  is unlocked, a rotation of the pivot member  2614  in the range of about 1 degree to about 45 degrees may cause a translation of the pivot slide  2612  in the range of about 0.01 mm to about 0.8 mm, although any suitable range for these respective movements are appreciated. For example, in some embodiments, a 10 degree rotation of the pivot member  2614  may cause a 0.5 mm translation in the pivot slide  2612 . As shown in  FIG.  26 F , the cam  2610  may intermittently lock the pivot member  2614  when the first and/or second pivot locks  2604   a ,  2604   b  settle back into the slot  2621  after the cam  2610  disengages the first and/or second pivot locks  2604   a ,  2604   b . In some embodiments, the cam  2610  may lift the first and/or second pivot locks  2604   a ,  2604   b  for a prescribed duration, the duration of which may be controlled by the cam shape and/or gearing. As a result, as the cam  2610  is rotated by the drive shaft  2608 , the first and second pivot locks  2604   a ,  2604   b  may move in opposing first and second vertical directions. Further, in some embodiments, the cam  2610  may rotate in either direction (e.g., clockwise and/or counterclockwise), and in other embodiments, the cam  2610  may rotate in only one direction (e.g., only clockwise or counterclockwise). With reference to  FIG.  26 H , various dimensions of the pivot lock mechanism  2600  are shown. However, it should be understood that while certain dimensions are shown in  FIG.  26 H , other suitable dimensions are also appreciated. 
       FIGS.  27 - 30    illustrate various types of spinal implant adjustment structures  2700 , according to some embodiments. The adjustment structures  2700  may be used, for example, to adjust one or more rods of the spinal implants shown in  FIGS.  1 - 12   . For example, the adjustment structures  2700  may be functionally similar to driving members  514  and  814  shown in  FIGS.  3 A and  12   . Similar to driving members  514  and  814 , the adjustment structures  2700  may be configured to engage first and second threaded drivers to cause pistoning of one or more corresponding rods. For example, with reference to implant structures illustrated in  FIG.  3 A , in some embodiments the adjustment structures  2700  may be used in lieu of driving member  514  to rotate the first and second threaded drives  528 ,  542  to cause the first and second rods  558 ,  588  to move into or out of the cavity  508  of the housing  502 , thereby causing the longitudinal distance L between points A and B to decrease or increase. Of course, it should be appreciated that any of the adjustment structures  2700  shown in  FIGS.  27 - 30    may be used as a driving member in any of the spinal implant embodiments described herein. 
     Each of the adjustment structures  2700  shown in  FIGS.  27 - 30    may be activated in a different way to rotate one or more threaded drivers and cause pistoning of one or more corresponding implant rods. For example,  FIG.  27    illustrates hydraulic activation,  FIG.  28    illustrates magnetic fluid pump activation, and  FIGS.  29  and  30    illustrate composite fluid coil spring activation. Similar to the driving members described above, the adjustment structures  2700  are configured to rotate one or more threaded drivers by delivering energy to them when activated. 
     As shown in  FIG.  27   , the hydraulic activated adjustment structure  2700  may be fluidically connected to a minimally invasive hydraulic system  2710 . The hydraulic system  2710  may include a fluid pump  2702 , first and second tubing segments  2703 ,  2710 , first and second hypo needles  2704 ,  2709 , and a fluid reservoir  2711 . The adjustment structure  2700  may include first and second cannulated rods  2714 ,  2715  into which the first and second hypo needs 2704, 2709 may be inserted after being inserted through the skin  2720  and subdermal tissue. In some embodiments, the first and second cannulated rods  2714 ,  2715  have one or more access points (e.g., access points  2712  and  2713 ) positioned along their length so that the first and second hypo needles  2704 ,  2709  may access the first and second cannulas  2705 ,  2708  of the first and second cannulated rods  2714 ,  2715 . Each access points may be, for example, a hole covered by septum such as a rubber stopper which prevents surrounding bodily fluid from entering the adjustment structure  2700 . 
     As shown in  FIG.  27   , the adjustment structure  2700  may include a chamber  2706  which houses an impeller  2707 . As fluid is pumped through the chamber  2706 , the impeller rotates. In some embodiments, the rotation of the impeller drives the first and second cannulated rods  2714 ,  2715 , and in some embodiments, the rotation of the impeller drives first and second threaded drivers (not shown), thereby causing pistoning of the first and second cannulated rods  2714 ,  2715 . Further, as shown in  FIG.  27   , in some embodiments, the chamber  2706  may be tapered into a nozzle at one end to increase the velocity of the fluid flowing past the impeller  2707 . In some embodiments, the first and second cannulas  2705 ,  2708  are the same or different sizes depending on the flow rate to be achieved across the impeller  2707 . In some embodiments, fluid is post-operatively delivered to the adjustment structure  2700  via a simple procedure such as an injection. The injected fluid may increase or decrease the length of the implant by turning the impeller  2707  as described above. In some embodiments, the fluid pumped by the hydraulic system may be saline, although any suitable fluid is appreciated. For example, in other embodiments, a biphasic fluid may be used so that its change in characteristics (e.g., volume) can be harnessed. For example, SF 6  (Sulfur Hexafluoride) or C 3 F 8  (Octafluoropropane) may be used. In addition, in some embodiments, a ratchet mechanism may be used in tandem to maintain device length change as the impeller rotates. 
       FIG.  28    generally illustrates an implant comprising a magnetically-driven impeller to drive fluid pressure and/or flow changes to cause pistoning adjustment of a rod which is dynamically sealed within a cavity of a housing. The adjustment structure  2700  illustrated in  FIG.  28    is similar to that shown in  FIG.  27    except that the impeller  2707  in  FIG.  28    is driven by a magnet rotor  2717  rather than fluid flow alone. In some embodiments, the magnetically-driven impeller  2707  drives fluid pressure and/or flow changes to cause pistoning adjustment of one or more rods (e.g., first and second cannulated rods  2714 ,  2715 ). In some embodiments, the one or more rods may be sealed within a cavity of a housing of the spinal implant, and in some embodiments, the one or more rods may be dynamically sealed within a cavity of a housing of the spinal implant. Although not shown, a hydraulic system may be connected to the adjustment structure  2700 . In some embodiments, the magnetically-driven impeller  2707  moves fluid from a first reservoir to a second reservoir of the hydraulic system. 
       FIG.  29    generally illustrates an implant having a support structure (e.g., a skeleton) that has an internal pressurized chamber or series of chambers that cooperatively maintain axial stiffness. By selectively removing fluid from one or more chamber (some or all of the fluid), the pressure may be controllably decreased, thereby lessening the total axial compression, and allowing the controlled shortening of the implant. Each chamber may be configured to be permanently punctured, wherein all of its fluid is removed, or may have a resealable skin, wherein a controlled amount of fluid may be removed, or even replaced.  FIG.  29    illustrates an adjustment structure  2700  comprising a composite fluid coil spring assembly  2902 . In some embodiments, the assembly  2902  includes a support structure  2904  (also referred to as a skeleton) and an extension spring  2906 . In some embodiments, the extension spring  2906  supplies a compressive force (i.e., potential energy) to the support structure  2904 . The support structure  2904  may include one or more fluid filled chambers  2905  that maintain the axial stiffness of the extension spring  2906 . In some embodiments, the chambers  2905  may be pressurized. By selectively removing fluid from one or more of the chambers  2905  (e.g., some or all of the fluid), the pressure in one or more of the chambers  2905  may be controllably decreased, thus lessening the total axial compression exerted by the extension spring  2906 , and thereby allowing the length of the implant to be controllably shortened. In some embodiments, each chamber may be configured to be permanently punctured, wherein all of its fluid is removed, or may have a resealable skin, wherein a controlled amount of fluid may be removed, or even replaced. By selectively replacing fluid into one or more the chambers  2905 , the pressure in one or more of the chambers  2905  may be controllably increased, thus increasing the total axial compression exerted by the extension spring  2906 , and thereby allowing the length of the implant to be controllably lengthened. The support structure  2904  thereby controls the amount of collapse and/or expansion of the extension spring  2906 . The one or more chambers  2905  store compressive energy by resisting the compressive force exerted by the extension spring  2906 . By selectively removing fluid from one or more of the chambers  2905  (e.g., some or all of the fluid), the extension spring  2906  becomes activated (i.e., it is allowed to compress). In some embodiments, a needle  2908  and a syringe  2910  may be used to remove fluid from one or more of the chambers  2905 , although any suitable fluid removal method and/or apparatus is appreciated. In some embodiments, saline may be used to fill the chambers  2905 , although any suitable fluid is appreciated. 
       FIG.  30    generally illustrates an implant that is similar to the embodiment in  FIG.  29   , but the “skeleton” is replaced by a compression spring. Fluid may be removed (as described in relation to  FIG.  29   ) or, as shown in  FIG.  30   , a magnetic release valve may be operated non-invasively (with an external magnetic field), to open an orifice to allow fluid to escape (pressure to decrease).  FIG.  30    illustrates a composite fluid coil spring assembly  3002  that is similar to the spring assembly  2902  shown in  FIG.  29   , but the support structure  2904  of spring assembly  2902  is replaced by a compression spring  3004 . Fluid may be removed or replaced as described above in relation to  FIG.  29   , or, as shown in  FIG.  30   , a magnetic release valve  3006  may be operated non-invasively (e.g., with an external magnetic field), to open an orifice to allow fluid to escape into a fluid reservoir  3008  and allow the pressure to decrease in the compression spring  3004 , thereby allowing the length of the implant to be controllably shortened. In some embodiments, fluid may be replaced in the compression spring  3004 , thereby allowing the length of the implant to be controllably lengthened. In some embodiments, the compression spring  3004  is installed in tension. The compression spring  3004  may store fluid in one or more pressurized compartments. In some embodiments, one or more of the compartments may be incrementally drained via the magnetic release valve  3006 . By selectively removing fluid from one or more of the chambers  2905  (e.g., some or all of the fluid), the compression spring  3006  becomes activated (i.e., it is allowed to compress). 
       FIGS.  31 A- 31 C  illustrate different types of springs  3100  that may be incorporated, for example into the embodiment of  FIG.  30   , to vary the application of force as conditions are varied. 
       FIG.  32    illustrates an implant  3200  having one or more shaped memory Nitinol wires  3202  in tension whose length may be made to change upon application of current (for example, non-invasively through inductive coupling, or via a battery  3204 ). A change in length of the Nitinol wires  3202  may cause a ratchet  3206  to controllably change the length of the implant  3200  by allowing a teethed bar  3208  to freely slide past. The Nitinol wires  3202  may store potential energy which may be activated remotely via electronics that apply current to the wires. In some embodiments, the application of current to the Nitinol wires causes the Nitinol wires to undergo a phase change, such as, for example, changing state and/or shape. For example, in some embodiments, the Nitinol wires  3202  contract when current is run through them, shortening the implant  3200 . Further, in certain embodiments, one or more of the Nitinol wires  3202  may be Nitinol springs. In some embodiments, the ratchet  3206  may be disengaged with the teethed rod  3208  when current is running through the wires  3202 . 
       FIG.  33    illustrates an implant  3300  having a magnetically operated rotational ratchet  3306  that allows the controlled rotation and compression of a lead screw  3302 . A torsion spring  3304  supplies the potential energy, such that, when the ratchet is in release mode, the lead screw  3302  is turned until the ratchet locks back down. As shown in  FIG.  33   , in some embodiments, the torsion spring  3304  may be a pre-wound spiral torsion spring, although any suitable torsion spring is appreciated. 
       FIGS.  34 A- 34 B  generally illustrate a harmonic drive that may be used together with any of the embodiments described herein, to increase efficiency (decrease losses, e.g., frictional losses). In some embodiments, a harmonic drive, also known as a strain wave gear, may be used. A harmonic drive, for example, the embodiments shown in  FIGS.  34 A and  34 B , may be used together with any of the embodiments described herein, to increase efficiency. Using a harmonic drive may decrease losses, such as, for example, frictional losses. Some advantages of using a harmonic drive include, but are not limited to, a possible extremely large gear reduction ( 150 : 1 ), an efficiency between 60-90% depending on the design, and the ability to have the input/output shafts generally along the same axis. In some embodiments, the gear reduction ratio may be 120:1. In some embodiments, the efficiency may be 82%. 
       FIG.  34 B  shows a harmonic drive  3400  with a wave generator  3410 , flex spline  3412 , and circular spline  3416 . Some advantages of a strain gear wave include, but are not limited to, lack of backlash, compactness and lightweight, high gear ratios, reconfigurable ratios within a standard housing, good resolution and excellent repeatability (linear representation) when repositioning inertial loads, high torque capability, and coaxial input and output shafts. High gear reduction ratios may be possible in small volume. For example, a harmonic drive may produce a ratio from 30:1 up to 320:1 in the same space in which planetary gears typically only produce a 10:1 ratio. 
     The wave generator  3410  is attached to an input shaft (not shown). The flex spline  3412  is like a shallow cup, where the sides of the flex spline  3412  are very thin but the bottom is thick and rigid. This results in significant flexibility of the walls at the open end due to the thin wall but rigidity in the closed side, where the closed side may be tightly secured, for example, to a shaft. Teeth  3414  are positioned radially around the outside of the flex spline  3412 . The flex spline  3412  fits tightly over the wave generator  3410 , so that when the wave generator plug is rotated, the flex spline  3412  deforms to the shape of a rotating ellipse but does not rotate with the wave generator  3410 . The flex spline  3412  may attach to an output shaft (not shown). The output shaft may have a maximum rating of 30-70 mNm. The circular spline  3416  is a rigid circular ring with teeth  3418  on the inside. The flex spline  3412  and wave generator  3410  are placed inside the circular spline  3416 , meshing the flex spline teeth  3414  and the circular spline teeth  3418 . Because the flex spline  3412  has an elliptical shape, its teeth  3414  only actually mesh with the circular spline teeth  3418  in two regions on opposite sides of the flex spline  3412  along the major axis of the ellipse. 
     In some embodiments, the wave generator  3410  may be the input rotation. As the wave generator plug rotates the flex spline teeth  3414  that are meshed with the circular spline teeth  3418  change. The major axis of the flex spline  3412  actually rotates with the wave generator  3410 , so the points where the teeth mesh revolve around the center point at the same rate as the wave generator  3410 . In some embodiments, there are fewer flex spline teeth  3414  than there are circular spline teeth  3418 , for example, two fewer teeth. This means that for every full rotation of the wave generator  3410 , the flex spline  3412  would be required to rotate a small amount, for example, two teeth, backward relative to the circular spline  3416 . Thus, the rotation of the wave generator  3410  results in a much slower rotation of the flex spline  3412  in the opposite direction. The gear reduction ratio may be calculated by: 
     
       
         
           
             
               reduction 
               ⁢ 
                   
               ratio 
             
             = 
             
               
                 ( 
                 
                   
                     flex 
                     ⁢ 
                         
                     spline 
                     ⁢ 
                         
                     teeth 
                   
                   - 
                   
                     circular 
                     ⁢ 
                         
                     spline 
                     ⁢ 
                         
                     teeth 
                   
                 
                 ) 
               
               
                 flex 
                 ⁢ 
                     
                 spline 
                 ⁢ 
                     
                 teeth 
               
             
           
         
       
     
     For example, if there are 200 flex spline teeth and  202  circular spline teeth, the reduction ratio is (200-202)/200=−0.01. Thus, the flex spline would spin at 1/100 the speed of the wave generator plug and in the opposite direction. 
       FIG.  35    generally illustrates a cycloidal drive that may be used together with any of the embodiments described herein. The cycloidal drive can allow for high ratios (thus significantly reduced speed, increase precision, increased torque delivery) in a small profile. The cycloidal disc (gold) is driven by an input shaft (green) having an eccentric bearing (green/white), thus turning the cycloidal disc in relation to the circumferentially oriented ring pins (white semi-circles) which are attached to the chassis. (The green shaft may be driven by a magnet or motor). The holes in the cycloidal disc drive the output disc (purple) via the pins (purple). In some embodiments, a cycloidal drive may be used, such as the cycloid drive illustrated in  FIGS.  35 A and  35 B . A cycloidal drive, also known as a cycloidal speed reducer is a mechanism for reducing the speed of an input shaft by a certain ratio. A cycloidal drive allows for high ratios in a small profile; thus, resulting in significantly reduced speed, increased precision, and increased torque delivery. The reduction ratio of the cycloidal drive may be obtained from: 
     
       
         
           
             
               reduction 
               ⁢ 
                   
               ratio 
             
             = 
             
               
                 ( 
                 
                   
                     number 
                     ⁢ 
                         
                     of 
                     ⁢ 
                         
                     ring 
                     ⁢ 
                         
                     pins 
                   
                   - 
                   
                     number 
                     ⁢ 
                         
                     of 
                     ⁢ 
                         
                     cycloidal 
                     ⁢ 
                         
                     disc 
                     ⁢ 
                         
                     lobes 
                   
                 
                 ) 
               
               
                 number 
                 ⁢ 
                     
                 of 
                 ⁢ 
                     
                 cycloidal 
                 ⁢ 
                     
                 disc 
                 ⁢ 
                     
                 lobes 
               
             
           
         
       
     
     In some embodiments, the reduction ratio may be up to 119:1 for single stage and up to 7569:1 for double stage. In some embodiments, the efficiency may approach 93% for single stage and approach 86% for double stage. 
     The cycloidal disc  3510  is driven by an input shaft  3512  mounted eccentrically to a bearing  3514 , thus turning the cycloidal disc  3510  in relation to the circumferentially oriented ring pins  3516  that are attached to the chassis. The cycloidal disc  3510  independently rotates around the bearing  3514  as it is pushed against the ring gear. The holes  3518  in the cycloidal disc  3510  drive the output disc  3520  via the pins  3522 . In some embodiments, the number of ring pins  3516  is larger than the number of lobes  3524  in the cycloidal disc  3510  causing the cycloidal disc  3510  to rotate around the bearing  3514  faster than the input shaft  3512  is moving it around, giving an overall rotation in the direction opposing the rotation of the input shaft  3512 . In some embodiments, the input shaft  3512  may be driven by a magnet or motor. 
       FIG.  36    generally illustrates a roller screw drive which may be used together with any of the embodiments described herein. The roller screw drive may allow for increased precision and torque magnification. A roller screw drive, such as the embodiment shown in  FIG.  36   , may be used together with any of the embodiments described herein. The roller screw drive may convert rotational motion to linear motion. The roller screw drive may allow for increased precision and torque magnification. In some embodiments, the roller screw drive has 75-90% efficiency. 
     The screw shaft  3610  has a multi-start V-shaped thread, which provides a helical raceway for multiple rollers  3612  radially arrayed around the screw shaft  3610  and encapsulated by a threaded nut  3614 . In some embodiments, the thread of the screw shaft  3610  is identical to the internal thread of the nut  3614 . In some embodiments, the thread of the screw shaft  3610  is opposite to the internal thread of the nut  3614 . 
     A spur gear, such as the embodiment shown in  FIG.  37   , may be used together with any of the embodiments described herein. In some embodiments, a spur gear may be used as a differential. The advantages of using a spur gear may include, but are not limited to, allowing one side to keep advancing even if the other side is stalled, increasing efficiency, being less complex and flexible, and being able to be designed to fit around a central screw. 
     A Torsen-type (also commonly known as a worm gear), such as the embodiment shown in  FIG.  38   , may be used together with any of the embodiments described herein. In some embodiments, a worm gear may be used as a differential. The advantages to using a worm gear differential may include, but are not limited to, allowing one side to keep advancing even if the other side has stalled, limiting or eliminating the ability to back-drive the system. 
     A differential screw, such as the embodiment shown in  FIG.  39   , may be used together with any of the embodiments described herein. A single screw  3910  has a first threaded portion  3911  having a first pitch A and a second threaded portion  3912  having a second pitch B. Both first threaded portion  3911  and second threaded portion  3912  have the threads in the same direction as each other. The screw  3910  may have a driving member (not shown) directly attached to the screw  3910  or attached to the screw  3910  via gearing, etc. The first housing portion  3921  may be attached to a first vertebra (not shown) and the second housing portion  3922  may be attached to a second vertebra (not shown). As the screw  3910  is turned (non-invasively) in a first rotational direction, the first housing portion  3921  moves in a first longitudinal direction in relation to the screw  3910  and the second housing portion  3921  moves in a first longitudinal direction in relation to the screw  3910 . However, because the second housing portion  3922  and the second threaded portion  3912  have a larger thread pitch B than the thread pitch A of the first housing portion  3921  and first threaded portion  3911 , the second housing portion  3922  begins to “overtake” the first housing portion  3921  and so the two housing portions move relatively closer to each other. The longitudinal distance that housings move relatively towards each other is equal to the difference in pitch (B-A) per turn of the screw. 
     In some embodiments, clutches, such as, for example, those shown in  FIGS.  40 A- 40 C , may be required to eliminate the ability for the system to back-drive. Two types of clutches may help: over running or on/off. Over running clutches only run in one direction, may lack controls, and may limit and/or eliminate the ability to drive the system in both directions. Examples of over running type clutches include: ratchet, needle clutch, free wheel, sprag clutch, spring clutch, face gear. On/off clutches may lock in either direction and need to be controlled (unlocked). Examples of on/off type clutches include: spring clutch with tang and face gears. 
     In some embodiments, a ball screw mechanism, such as, for example, the embodiment shown in  FIG.  41   , may be used together with any of the embodiments described herein, to increase efficiency, and decrease losses (e.g., frictional losses). Using a ball screw mechanism may decrease losses, for example, frictional losses. In some embodiments, a ball screw mechanism may translate rotational to linear motion. The ball bearings  4114  fit between the screw shaft  4110  and the nut  4112 . The ball bearings  4114  may reduce friction and input torque and as a result improve efficiency. 
       FIGS.  42 - 44    illustrate three different systems of torque split, differential, and/or gear reduction. The features shown in  FIGS.  42 - 44    may be used in various combinations, not all of which may be shown in the figures. The flow charts show some embodiments of systems, where a signal or signals from an external communicator results in compression. In some embodiments, as illustrated by system  4200  in  FIG.  42   , an external communicator  4210  may generate and transmit a signal  4212  to a motor  4214  in subsystem  4205 . The motor output torque  4216  determines how much, if any, gear reduction  4218  is required. The high torque  4220  is split over a differential  4222 . In some embodiments, the torque split ratio can vary from 100/0 to 50/50. In some embodiments, the torque split ratio is 50/50 so that half the high torque is transmitted to a first side  4224  and half the high torque is transmitted to a second side  4226 . In some embodiments, the high torque on the first side  4224  may be converted from rotary to linear motion  4230  resulting in compression to the first side  4228 . In some embodiments, the high torque on the second side  4226  may be converted from rotary to linear motion  4232  resulting in compression on the second side  4234 . In some embodiments, the rotary to linear motion conversion mechanisms on the first and second sides  4230  and  4232  are the same or substantially similar. In some embodiments, the rotary to linear motion conversion mechanisms on the first and second sides  4230  and  4232  are different. In some embodiments, the amounts of compression on the first and second sides  4228  and  4234  are the same or substantially similar. In some embodiments, the amounts of compression on the first and second sides  4230  and  4232  are different. 
     In some embodiments, as illustrated by system  4300  in  FIG.  43   , an external communicator  4310  may generate and transmit a signal  4312  to a motor  4314 . The motor output torque  4316  is split over a differential  4318 . In some embodiments, the torque split ratio can vary from 100/0 to 50/50. In some embodiments, the torque split ratio is 50/50 so that half the torque is transmitted to a first side  4320  and half the torque is transmitted to a second side  4322 . In some embodiments, the torque on the first side  4320  is transferred by gear reduction  4326  to increase the amount of torque, resulting in a high torque  4324 . In some embodiments, the torque on the second side  4322  is transferred by gear reduction  4328  to increase the amount of torque, resulting in a high torque  4330 . In some embodiments, the first side gear reduction  4326  is by the same value as the second side gear reduction  4326 . In some embodiments, the first and second sides have different gear reduction values. In some embodiments, the first and second gear reductions may be done by similar reduction drives. In some embodiments, the first and second gear reductions may be done by the different style reduction drives. In some embodiments, gear reduction  4326  or  4328  may not be necessary, depending on the value of the torque  4320  or  4322 . In some embodiments, the high torque on the first side  4324  may be converted from rotary to linear motion  4334  resulting in compression to the first side  4332 . In some embodiments, the high torque on the second side  4330  may be converted from rotary to linear motion  4336  resulting in compression on the second side  4338 . In some embodiments, the rotary to linear motion conversion mechanisms on the first and second sides  4334  and  4336  are the same or substantially similar. In some embodiments, the rotary to linear motion conversion mechanisms on the first and second sides  4334  and  4336  are different. In some embodiments, the amounts of compression on the first and second sides  4332  and  4338  are the same or substantially similar. In some embodiments, the amounts of compression on the first and second sides  4332  and  4238  are different. 
     In some embodiments, as illustrated by system  4400  in  FIG.  44   , an external communicator  4410  may generate and transmit a first signal  4412  and a second signal  4414  to a first motor  4416  and a second motor  4418 , respectively. In some embodiments, the external communicator may generate and transmit at least one signal, such as, for example, one, two, ten, or one hundred signals. In some embodiments, the first signal  4412  and the second signal  4414  are the same or substantially similar. In some embodiments, the first and second signals  4412  and  4414  are different. The first motor  4416  is part of a subsystem  4405  and the second motor  4418  is part of a subsystem  4415 . The motor output torques  4420  and  4422  determine how much, if any, gear reduction  4424  and  4426  is required. In some embodiments, the first motor output torque  4420  and the second motor output torque  4422  are the same or substantially similar values. In some embodiments, the first and second motor output torques  4420  and  4422  are different values. In some embodiments, there may be no gear reduction. In some embodiments, the high torque on the first side  4428  may be converted from rotary to linear motion  4432  resulting in compression to the first side  4336 . In some embodiments, the high torque on the second side  4430  may be converted from rotary to linear motion  4434  resulting in compression on the second side  4438 . In some embodiments, the rotary to linear motion conversion mechanisms on the first and second sides  4432  and  4434  are the same or substantially similar. In some embodiments, the rotary to linear motion conversion mechanisms on the first and second sides  4432  and  4434  are different. In some embodiments, the amounts of compression on the first and second sides  4436  and  4438  are the same or substantially similar. In some embodiments, the amounts of compression on the first and second sides  4436  and  4438  are different. 
       FIGS.  45 A- 45 C  generally illustrate various types of a pivot for coupling to pedicle screws, which are able to turn only in a single direction, thus allowing, for example, an increase in lordosis, without a loss. This, the implant will be adjustable only in a first angular direction, and will not allow back adjustment in the opposite angular direction.  FIG.  45 C  illustrates a pivot with a sprag clutch. In some embodiments, a one way locking pivot, such, as for example, the embodiments shown in  FIGS.  45 A- 45 C , may be used for coupling to pedicle screws. The pivot may move in one rotational direction but not the other. In some embodiments, for example, the pivot may be configured to be movable in the rotational direction at which lordosis is increased and not be movable in the opposite direction; thus, increasing lordosis without a loss. In some embodiments, the pivot may comprise a freewheel or other one-way clutching concepts presented herein. Alternatively, one way pivoting may be provided by a ratchet or other type of commonly known device allowing rotation in one way but not the other. In some embodiments, the pivot may comprise a sprag clutch, such as for example, the embodiments shown in  FIGS.  46 A and  46 B . Using a pivot may allow an extra degree of freedom for lordotic compression but may limit how much compression. 
       FIG.  47    shows an embodiment where the pivot&#39;s 4710 rotation is controlled by axial movement (e.g., retraction) of an implant. In some embodiments, a pivot may include extension members  4712  that are partially constrained. For example, they may be constrained in a single linear degree of freedom, for example, slidable in a groove or slot  4713  or  4714 . A first linkage  4715  and a second linkage  4716  are similar to the boom and stick of a backhoe. The housing  4718  and rod  4720  are similar to the backhoe cylinder. Noninvasive shortening of the length of the implant (via retraction of rod  4720  into housing  4718 ) allows slots  4713  and  4714  of first linkage  4715  and second linkage  4716 , respectively, slide along the housing extension member, which attaches the housing  4722  to the middle pedicle screw that is connected to vertebra B. The two outer extension members  4712  are rigidly secured respectively to the first and second linkages  4715  and  4716 , and thus, they cause the two outer pedicle screws to rotate and force an increase of lordosis between vertebra A and vertebra C. 
     In some embodiments, a torque-limiting brake that is configured to lock and unlock a pivot may be used, such as, for example, the embodiment shown in  FIG.  48   . The pivot may allow for changes in angulation, such as to change an angle of lordosis. At a threshold torque, slippage occurs at point A, thus unlocking the brake and allowing the pivot  4810  to temporarily unlock. 
     Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow. Therefore, in addition to the many different types of implantable retraction or distraction devices that are configured to be non-invasively adjusted, implantable non-invasively adjustable non-distraction devices are envisioned, including, for example, adjustable restriction devices for gastrointestinal disorders such as GERD, obesity, or sphincter laxity (such as in fecal incontinence), or other disorders such as sphincter laxity in urinary incontinence. These devices, too, may incorporate magnets to enable the non-invasive adjustment. 
     Similarly, this method of disclosure, is not to be interpreted as reflecting an intention that any claim require more features than are expressly recited in that claim. Rather, as the following claims reflect, inventive aspects lie in a combination of fewer than all features of any single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment.