Abstract:
The present disclosure describes a spinal fixation system comprising a telescoping spinal rod, as well as methods of its use and a guide tower for use therewith. The telescoping rod can be extended after it has been inserted into the patient below the fascia, which permits it to be extended in the sub-fascial space.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application PCT/US17/17693, filed 13 Feb. 2017 (pending). International Application PCT/US17/17693 cites the priority of U.S. Patent Application No. 62/295,001, filed on 12 Feb. 2016 (expired). The contents of both of the foregoing applications are incorporated by reference herein in their entireties. 
     
    
     BACKGROUND 
     Field 
       [0002]    The present disclosure relates generally to medical devices, and specifically to surgical instruments and methods for performing spinal procedures. 
       Background 
       [0003]    The spine is critical in human physiology for mobility, support, and balance. The spine protects the nerves of the spinal cord, which convey commands from the brain to the rest of the body, and convey sensory information from the nerves below the neck to the brain. Even minor spinal injuries can be debilitating to the patient, and major spinal injuries can be catastrophic. The loss of the ability to bear weight or permit flexibility can immobilize the patient. Even in less severe cases, small irregularities in the spine can put pressure on the nerves connected to the spinal cord, causing devastating pain and loss of coordination. 
         [0004]    The spinal column is a bio-mechanical structure composed primarily of ligaments, muscles, bones, and connective tissue that forms a series of vertebral bodies stacked one atop the other and intervertebral discs between each vertebral body. The spinal column provides support to the body and provides for the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs; complex physiological motion between these parts; and protection of the spinal cord and the nerve roots. 
         [0005]    The stabilization of the vertebra and the treatment for spinal conditions is often aided by a surgically implanted fixation device which holds the vertebral bodies in proper alignment and reduces the patient&#39;s pain and prevents neurologic loss of function. Spinal fixation is a well-known and frequently used medical procedure. Spinal fixation systems are often surgically implanted into a patient to aid in the stabilization of a damaged spine or to aid in the correction of other spinal deformities. Existing systems often use a combination of rods, plates, pedicle screws, bone hooks, locking screw assemblies, and connectors, for fixing the system to the affected vertebrae. The system components may be rigidly locked together to fix the connected vertebrae relative to each other, stabilizing the spine until the bones can fuse together. 
         [0006]    A spinal rod is often anchored to two or more vertebrae to immobilize the spine between the two vertebrae. To reduce tissue trauma and opportunity for infection, there have been attempts to develop minimally invasive approaches. Sometimes, minimally invasive rod insertion includes advancing the rod towards the anchors through a guide and then angling a rod inserter to rotate the rod to a position that is in line with the rod channels in the anchors. Because of the limited space available to maneuver the rod, the longer the rod is the more challenging the insertion becomes. This creates two problems. The awkwardness in guiding a rod of sufficient length to connect the desired vertebrae can result in errors, such as passing the rod above the fascia. It also results in limiting the lengths of the rod that can be inserted in a minimally invasive manner. 
         [0007]    Consequently there is a need in the art for a way to insert longer rods below the patient&#39;s fascia in a minimally invasive manner. 
       SUMMARY 
       [0008]    The present disclosure describes a spinal fixation system comprising a telescoping spinal rod, as well as methods of its use and a guide tower for use therewith. The telescoping rod can be extended after it has been inserted into the patient below the fascia, which permits it to be extended in the sub-fascial space. 
         [0009]    In a first aspect, a system for spinal fixation is provided, the system comprising: a bone anchor including a distal bone fastener member, a proximal rod housing comprising a rod channel; and a telescoping spinal rod dimensioned to fit within the rod channel, the telescoping spinal rod having an extended configuration and a collapsed configuration, wherein the telescoping spinal rod has a first longitudinal length in the collapsed configuration and a second longitudinal length in the extended configuration, and wherein the first longitudinal length is less than the distance between a vertebral pedicle in a subject and an adjacent vertebral pedicle in the subject. 
         [0010]    In a second aspect, a system for spinal fixation is provided, the system comprising: a bone anchor including a bone fastener member, a first rod housing comprising a first rod channel, and a second rod housing comprising a second rod channel; a first telescoping spinal rod positioned within the first rod channel, the first telescoping spinal rod having an extended configuration and a collapsed configuration; and a second telescoping spinal rod positioned within the second rod channel, the second telescoping spinal rod having an extended configuration and a collapsed configuration; wherein the first telescoping spinal rod and second telescoping spinal rod extend in opposite directions from the bone anchor. 
         [0011]    In a third aspect, a guide tower assembly for guiding a spinal rod into position from a first bone anchor to a second bone anchor is provided, the guide tower assembly comprising: an elongate tower member having a proximal end, a distal end, and a longitudinal axis; a lumen running from the proximal end to the distal end of the elongate tower member; a longitudinal slot in the elongate tower member that connects to the lumen; a bone anchor engagement member at the distal end of the tower member configured to reversibly fasten the elongate tower member to a rod housing of the first bone anchor; a first rod holder having a first rod engagement feature at a distal end of the rod holder and a first translating shaft connected to the first rod engagement feature, wherein the first translating shaft is capable of translating relative to the elongate tower member parallel to the longitudinal axis of the elongate tower member, and wherein the first rod engagement feature translates with the first translating shaft; a second rod holder having a second rod engagement feature at a distal end of the second rod holder and a second translating shaft connected to the second engagement feature, wherein the second translating shaft is capable of translating relative to the elongate tower member parallel to the longitudinal axis of the elongate tower member, wherein the second rod engagement feature translates with the second translating shaft and wherein the second translating shaft is capable of translating at a different velocity than a velocity of translation of the first translating shaft. 
         [0012]    In a fourth aspect, a method of fixating a first vertebra to a second vertebra is provided, comprising: fastening a first bone anchor to the first vertebra; fastening a second bone anchor to a second vertebra; inserting a telescoping spinal rod into the first bone anchor in a collapsed configuration, the telescoping spinal rod having an extended configuration and the collapsed configuration, wherein the telescoping spinal rod has a collapsed length that is shorter than a length between the first bone anchor and the second bone anchor, and an extended length that is no shorter than the length between the first bone anchor and the second bone anchor; extending the telescoping spinal rod from the collapsed to the extended configuration, to cause the telescoping spinal rod to extend into the second bone anchor; locking the telescoping spinal rod in position in the first bone anchor; and locking the telescoping spinal rod in position in the second bone anchor. 
         [0013]    The above presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key or critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1 . A side view of an embodiment of the system for spinal fixation, showing a telescoping spinal rod seated in the rod channel of a bone anchor while in its retracted position. The skin (S) and fascia (F) of the subject are shown. 
           [0015]      FIG. 2 . A side view of an embodiment of the system for spinal fixation, showing a telescoping spinal rod seated in the rod channel of a bone anchor while in its expanded position. 
           [0016]      FIG. 3 . A cross-sectional side view of an embodiment of the telescoping spinal rod. 
           [0017]      FIG. 4 . A transverse cross-sectional view of a subject into whom has been implanted an embodiment of the telescoping spinal rod, showing an embodiment of an external adjustment device positioned to cause the spinal rod to extend or retract. 
           [0018]      FIG. 5 . A side view of an embodiment of the system for spinal fixation in situ, showing guide towers in place holding the telescoping spinal rod. 
           [0019]      FIG. 6 . An embodiment of the system for spinal fixation with a bidirectional telescoping rod in the retracted position. 
           [0020]      FIG. 7 . The embodiment of the system for spinal fixation with a bidirectional telescoping rod shown in  FIG. 6 , in the extended position. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Illustrative embodiments of a system for spinal fixation, parts, and methods for use thereof, are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The system for spinal fixation, parts, and methods for use thereof disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
         [0022]    A system for spinal fixation  5  is provided, useful for minimally invasive approaches. In a general embodiment shown in  FIG. 1 , the system comprises a bone anchor  10  and a telescoping spinal rod  15  configured to be fastened to the bone anchor  10 . The telescoping rod  15  is capable of assuming an extended configuration and a collapsed configuration. Embodiments of the telescoping rod  15  may also be capable of assuming intermediate configurations, in which the rod  15  is neither maximally extended nor maximally collapsed. In the collapsed configuration the rod  15  has a first longitudinal length, and in the extended configuration it has a second longitudinal length that is longer than the first longitudinal length. The first (collapsed) longitudinal length is less than the distance between a vertebral pedicle in a subject and an adjacent vertebral pedicle in the subject. The second (extended) longitudinal length is at least the distance between a vertebral pedicle in a subject and an adjacent vertebral pedicle in the subject. Thus, when extended, the rod is capable of connecting two adjacent pedicles. 
         [0023]    The bone anchor  10  functions to limit the movement of the rod  15  relative to the vertebra. Such bone anchors  10  include bone screws, ties, hooks, and other such anchors as known in the art. In a specific embodiment the bone anchor  10  is a pedicle screw  20 . The pedicle screw  20  comprises a distal bone screw  25  fastened to a proximal rod housing  30 . The rod housing  30  may be of the “tulip” type, having two arms  35  extending proximally to form a rod channel  40  in between. Such tulips typically have helical flanges or screw threads on the interior surface, to allow a fixation screw to be inserted to reduce and lock the position of a spinal rod, once it is seated in the rod channel. The pedicle screw  20  may not allow relative movement between the bone screw  25  and the rod housing  30 , or it may allow deflection of the rod housing  30  relative to the bone screw  25 . The deflection may occur about exactly one axis (uniaxial) or it may occur about multiple axes (multiaxial). In a specific embodiment the rod housing  30  swivels relative to the bone screw  25  like a universal joint. 
         [0024]    As shown in  FIG. 1 , one or more guide assemblies  500  may be used with the system. Such a guide assembly may comprise an elongate tower member having a proximal end, a distal end, and a longitudinal axis; a lumen running from the proximal end to the distal end of the elongate tower member; a longitudinal slot in the elongate tower member that connects to the lumen; and a bone anchor engagement member at the distal end of the tower member configured to reversibly fasten the elongate tower member to a rod housing of the first bone anchor. The rod is inserted into the guide tower assembly and translated distally though the lumen and longitudinal slot, with or without the assistance of an inserter. The guide assemblies  500  can be reversibly fastened to the bone anchors by minimally invasive techniques. The short length of the rod on insertion (in its retracted configuration) limits the back angle necessary to rotate the rod, which makes it easier to get under the subject&#39;s fascia and keep the incision small. The rod is then extended once it is positioned in the rod housing. 
         [0025]    Some embodiments of the system  5  are configured to allow the telescoping rod to be inserted towards the first bone anchor with the rod axis generally parallel to the guide assembly. The rod is then reoriented to a position with the rod axis generally perpendicular to the guide assembly prior to adjusting the rod to the extended position, the distal end of the rod passing through the longitudinal slot and underneath the fascia. 
         [0026]    Some embodiments of the telescoping spinal rod  15  are configured to elongate and contract upon receipt of a remote signal. Such embodiments have the advantage of allowing the rod  15  to be modified in length during a procedure without inserting an additional instrument into the patient. Such embodiments of the rod  15  also have the advantage of allowing the rod  15  to be modified in length postoperatively without an invasive procedure. The remote signal may be an electromagnetic signal, such as a rotating magnetic field. A specific mechanism for transforming a rotating magnetic field into extension or contraction of the spinal rod  15  is a magnet operatively coupled to the rod (“rod magnet”)  45  configured to rotate in the presence of the rotating magnetic field, which in turn causes the rod  15  to elongate or contract. Whether the rod  15  elongates or contracts may depend on the direction of the magnetic field&#39;s rotation. The rod magnet  45  will be composed of a magnetic material, such as a ferromagnetic material. 
         [0027]    A specific embodiment of the telescoping spinal rod  15  is shown in  FIG. 3 . As shown, the telescoping spinal rod  15  comprises: a first elongate element containing a cavity  55 ; a second elongate element  60  dimensioned to at least partially fit within the cavity  55 , and having an internally threaded region  65 ; and a lead screw  70  coupled to rotate when the rod magnet  45  rotates, and comprising an externally threaded region  75  engaged to the internally threaded region  65  of the second elongate element  60 , such that rotation of the lead screw  70  causes the second elongate element  60  to translate relative to the first elongate element  50 . In this embodiment the rod magnet  45  rotates about approximately the longitudinal axis of the telescoping rod  15 , and directly drives the rotation of the lead screw  70 . The lead screw&#39;s  70  rotation in turn causes longitudinal translation of the second elongate element  60 , causing it to either extend from or contract into the first elongate element  50 . A dynamic seal  80  may advantageously be present at the interface between the first  50  and second  60  elongate elements to prevent intrusion of fluids into the interior of the rod  15 . 
         [0028]    Alternatively, the rod  15  may be configured such that the rod magnet  45  indirectly drives the rotation of the lead screw  70 , for example through a gear train  85 . The use of a gear train  85  has the advantage of allowing an unequal ratio between the angular motion of the rod magnet  45  and the angular motion of the lead screw  70 . For example, if the gear ratio is less than 1:1 (screw  70 : magnet  45 ), then delicate changes in the length of the rod  15  may be accomplished, and increased torque may be realized with less force. On the other hand, if the gear ratio is greater than 1:1, the length of the telescoping rod  15  may be modulated at greater speeds with less torque. 
         [0029]    An alternative embodiment of the system  5  employs a bone anchor  10  with two rod housings ( 30   a,    30   b ), to allow two telescoping rods ( 15   a,    15   b ) to be fastened to the bone anchor  10 . The two rods ( 15   a,    15   b ) are configured to telescope in different directions. This allows rods to be extended from the first vertebra to two adjacent vertebra (one cranial to the first vertebra and one caudal to the first vertebra) through the same small incision. The alternative embodiment of the system comprises a bone anchor  10  including a bone fastener member  90 , a first rod housing  30   a  comprising a first rod channel  40   a,  and a second rod housing  30   b  comprising a second rod channel  40   b;  a first telescoping spinal rod  15   a  positioned within the first rod channel  40   a,  the first telescoping spinal rod  15   a  having an extended configuration and a collapsed configuration; and a second telescoping spinal rod  15   b  positioned within the second rod channel  40   b,  the second telescoping spinal rod  15   b  having an extended configuration and a collapsed configuration; wherein the first telescoping spinal rod  15   a  and second telescoping spinal rod  15   b  extend in opposite directions from the bone anchor  10 . One or both of the telescoping rods ( 15   a,    15   b ) may have any structure or properties that are disclosed as suitable for the telescoping rod  15  in the unidirectional system described above. 
         [0030]    An alternative embodiment of the system  5  employs a bone anchor  10  with a single rod housing containing a bidirectional telescoping rod  400  to be fastened to the bone anchor  10 . The bidirectional telescoping rod is configured to telescope in different directions. This allows the rod  400  to be extended from the first vertebra to two adjacent vertebra (one cranial to the first vertebra and one caudal to the first vertebra) through the same small incision. The alternative embodiment of the system comprises a bone anchor  10  including a bone fastener member  90 , a first rod housing  30  comprising a first rod channel  40 ; a bidirectional telescoping spinal rod  400  positioned within the first rod channel  40 , the bidirectional telescoping spinal rod  400  having an extended configuration and a collapsed configuration; wherein the bidirectional telescoping spinal rod  400  extends in two opposite directions from the bone anchor  10 . The bidirectional telescoping rod  400  comprises a first elongate member  410  having a cavity  415 , a second elongate member  420  configured to fit within the cavity  415 , a third  430  elongate member configured to fit within the cavity  415 , and an extension mechanism  440  configured to extend the second  420  and third  430  elongate members from the first elongate  410  member in response to a remote signal, such as a rotating magnetic field. The extension mechanism  440  may comprise a rotatable magnet  445 , the rotation of which causes the second  420  and third  430  elongate members to extend. 
         [0031]    The system  5  is at least partially composed of a biocompatible non-absorbable material. Specific examples of such suitable materials include titanium, alloys of titanium, steel, and stainless steel. Parts of the system  5  could conceivably be made from non-metallic biocompatible materials, which include aluminum oxide, calcium oxide, calcium phosphate, hydroxyapatite, zirconium oxide, and polymers such as polypropylene. 
         [0032]    A guide tower assembly for the inserter-less introduction of a spinal rod is provided. It functions by connecting to a spinal rod at two points, and translating the two points in a distal direction at different velocities. As shown in  FIG. 5 , a general embodiment of the guide tower  95  comprises an elongate tower member  100  having a proximal end  105 , a distal end  110 , and a longitudinal axis. A lumen  115  is present within the elongate tower member, running from the proximal end  105  to the distal end  110 . A longitudinal slot  120  in the elongate tower member  100  connects the lumen  115  to the exterior of the guide tower  95 . A bone anchor engagement member  125  is located at the distal end  110  of the tower member, and is configured to reversibly fasten the elongate tower member  100  to a rod housing  30  of the first bone anchor  10 . The spinal rod is held by a first rod holder  130  having a first rod engagement feature  135  at a distal end of the rod holder  15  and a first translating shaft  140  connected to the first rod engagement feature  135 , wherein the first translating shaft  140  is capable of translating relative to the elongate tower member  100  parallel to the longitudinal axis of the elongate tower member  100 , and wherein the first rod engagement feature  135  translates with the first translating shaft  140 ; thus the rod can be raised and lowered (i.e., translated proximally or distally) using the translating rod. The guide tower  95  also includes a second rod holder  145  having a second rod engagement feature  150  at a distal end of the second rod holder  145  and a second translating shaft  155  connected to the second engagement feature  150 , wherein the second translating shaft  155  is capable of translating relative to the elongate tower member  100  parallel to the longitudinal axis of the elongate tower member  100 , wherein the second rod engagement feature  150  translates with the second translating shaft  155 . In order to rotate the spinal rod as it is lowered, the second translating shaft  155  is capable of translating at a different velocity than a velocity of translation of the first translating shaft  140 . 
         [0033]    The lumen  115  in the guide tower assembly  95  is dimensioned to allow the spinal rod to pass through the elongate tower member  100  longitudinally. The longitudinal slot  120  is likewise dimensioned to allow the spinal rod  15  to pass through, and permits the spinal rod to have a length greater than the diameter of the elongate tower member  100 . Some embodiments of the guide tower assembly  95  have two longitudinal slots ( 120   a,    120   b ) in the elongate tower member  100 , positioned opposite one another, which allows the spinal rod to protrude from both slots ( 120   a,    120   b ). 
         [0034]    The rod holders ( 130 ,  145 ) keep the rod in place while it is guided into the rod housing  30  of the bone anchor  10 . The rod holders ( 130 ,  145 ) may be configured to securely hold the rod before it is seated in the rod channel  40 , but to release the rod once the rod is seated. One such embodiment, shown in  FIG. 5 , is a pincer comprising two semicircular fingers. 
         [0035]    In operation, the guide tower assembly  95  functions by lowering each end of the spinal rod at different rates. This can be accomplished by various means. For example, each of the translating shafts ( 140 ,  155 ) may be threaded, with different thread pitches. Thus, when rotated at the same rate, each shaft ( 140 ,  155 ) translates at a different velocity. Rotation of the shafts ( 140 ,  155 ) may be provided by various means, such as by operatively connecting a given shaft to a magnet (“shaft magnet”)  160  such that rotation of the shaft magnet  160  causes the threaded shaft ( 140 ,  155 ) to translate parallel to the longitudinal axis of the guide tower  95 . The shaft magnet  160  may be mounted to rotate when exposed to a rotating magnetic field. In such embodiments, upon exposure to a rotating magnetic field, one or both of the translating shafts ( 140 ,  155 ) will be caused to translate, possibly at different rates. The shaft magnet  160  may drive rotation of the translating shaft ( 140 ,  155 ), for example if the translating shaft ( 140 ,  155 ) is threaded. The shaft magnet  160  may drive rotation of the translating shaft ( 140 ,  155 ) directly (for example if the shaft magnet  160  is mounted to the shaft ( 140 ,  155 ) in such a way that its axis of rotation is coaxial with the shaft&#39;s ( 140 ,  155 ) axis of rotation), or indirectly. In embodiments in which the shaft magnet  160  drives the translating shaft ( 140 ,  155 ) indirectly, it may do so by means of a gear train  85 . The shaft magnet  160  may be made of any magnetic material disclosed above as suitable for the rod magnet  45 . In some embodiments of the guide tower assembly  95 , the rest of the guide tower assembly  95  is made of a non-magnetic material or weakly magnetic material, to prevent interference with the movement of the shaft magnet  160 . Specific examples of such nonmagnetic non-absorbable biocompatible material include titanium, alloys of titanium, aluminum oxide, calcium oxide, calcium phosphate, hydroxyapatite, zirconium oxide, and polymers such as polypropylene. Examples of weakly magnetic materials include paramagnetic materials and diamagnetic materials. In a specific embodiment, the weakly magnetic material is austenitic stainless steel. 
         [0036]    The utility of the system  5  described above may be enhanced through the use of the guide tower assembly  95 . Some embodiments of the guide tower assembly  95  may be specially configured to guide. a telescoping spinal rod  15  of the kind described above into position through a small incision. In other embodiments the guide tower is used to guide a conventional spinal rod into position. 
         [0037]    A method of fixating a first vertebra to a second vertebra is provided by a minimally invasive approach. A general embodiment of the method comprises fastening a first bone anchor  10   a  to the first vertebra; fastening a second bone anchor  10   b  to a second vertebra; inserting a telescoping spinal rod  15  into the first bone anchor  10   a  in a collapsed configuration; extending the telescoping spinal rod  15  from the collapsed to the extended configuration, to cause the telescoping spinal rod  15  to extend into the second bone anchor  10   b;  locking the telescoping spinal rod  15  in position in the first bone anchor  10   a;  and locking the telescoping spinal rod  15  in position in the second bone anchor  10   b.  Locking may be performed by a variety of methods, such as by inserting a locking screw  165  into the rod housing  30  and tightening it against the rod  15 . As discussed above, the telescoping spinal rod  15  has an extended configuration and the collapsed configuration, such that the telescoping spinal rod  15  has a collapsed length that is shorter than a length between the first bone anchor  10   a  and the second bone anchor  10   b,  and an extended length that is no shorter than the length between the first bone anchor  10   a  and the second bone anchor  10   b.    
         [0038]    The method may be used with a bone anchor  10  having two rod housings ( 30   a,    30   b ). In that case, the method will further comprise fastening a third bone anchor  10   c  to a third vertebra; inserting a second telescoping spinal rod  15   b  into the second rod housing  30   b  (on the first bone anchor  10   a ) in a collapsed configuration; extending the second telescoping spinal rod  15   b  from the collapsed to the extended configuration, to cause it to extend into the third bone anchor  10   c;  locking the telescoping spinal rod  15   b  in position in the second rod housing  30   b;  and locking the telescoping spinal rod  15   b  in position in the third bone anchor  10   c.    
         [0039]    In some embodiments of the method, the telescoping spinal rod  15  is extended from the collapsed to the extended configuration while said telescoping spinal rod  15  is below the fascia of the subject. Such embodiments of the method have the advantage of connecting two vertebrae without requiring an incision to run between them, as would be required if the spinal rod  15  were implanted while at its full length. In such cases the rod  15  may be configured to extend or contract in response to a remote signal, such as an electromagnetic signal. As described above, one such type of electromagnetic signal is a rotating magnetic field. This may be accomplished using an external rotating magnet  170  or array of magnets, or using an electrically induced magnetic field. One embodiment of the external adjustment device  180  (shown in  FIG. 4 ) is configured for placement on or adjacent to the skin of the subject and includes at least one magnet (“external magnet”)  170  configured for rotation. The illustrated embodiment also has a motor  185  configured to rotate the external magnet  170 , whereby rotation of the external magnet  170  effectuates rotational movement of the rod magnet  45 . As shown in  FIG. 4 , the external adjustment device  180  may have two external magnets ( 170   a,    170   b ). The two external magnets ( 170   a,    170   b ) may be configured to rotate at any suitable rate, and in a specific embodiment they are configured to rotate at the same rate. In further embodiments the external magnets ( 170   a,    170   b ) are configured to rotate at the same rate such that the positive and negative poles of each external magnet ( 170   a,    170   b ) are aligned. Stated another way, in such embodiments the positive (“North”) pole of the first external magnet  170   a  will be at 0° when the positive pole of the second external magnet  170   b  is at 180°, and the negative (“South”) pole of the first external magnet  170   a  will be at 180° when the negative pole of the second external magnet  170   b  is at 0° (such a configuration is shown in  FIG. 4 ). Because both external magnets ( 170   a,    170   b ) rotate in the same direction along parallel axes at the same rate this relative configuration will be preserved through multiple cycles. 
         [0040]    The foregoing description illustrates and describes the processes, machines, manufactures, compositions of matter, and other teachings of the present disclosure. Additionally, the disclosure shows and describes only certain embodiments of the processes, machines, manufactures, compositions of matter, and other teachings disclosed, but, as mentioned above, it is to be understood that the teachings of the present disclosure are capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the teachings as expressed herein, commensurate with the skill and/or knowledge of a person having ordinary skill in the relevant art. The embodiments described hereinabove are further intended to explain certain best modes known of practicing the processes, machines, manufactures, compositions of matter, and other teachings of the present disclosure and to enable others skilled in the art to utilize the teachings of the present disclosure in such, or other, embodiments and with the various modifications required by the particular applications or uses. Accordingly, the processes, machines, manufactures, compositions of matter, and other teachings of the present disclosure are not intended to limit the exact embodiments and examples disclosed herein. Any section headings herein are provided only for consistency with the suggestions of 37 C.F.R. §1.77 and related laws or otherwise to provide organizational queues. These headings shall not limit or characterize the invention(s) set forth herein.