Abstract:
Correction of a scoliotic curve in a spine comprises the steps of implanting an expanding rod isolated completely under the skin and attached to selected portions of the scoliotic curve of the spine at opposing ends of the rod; and producing a controlled force by means of expansion of the rod over at an extended time period under external control until a desire spinal curve is obtained. An incremental force is generated to stretch the scoliotic curve of the spine between the selected portions where attachment of the rod is defined. The controlled force is provided steadily for at least one month or alternatively 1-3 months. Multiple rods may be employed each associated with a different scoliotic curve of the spine or a different portion of the scoliotic curve.

Description:
RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 11/172,678 filed on Jun. 30, 2005, which itself claims priority to U.S. Provisional Patent Application Ser. No. 60/584,961, filed on Jul. 2, 2004, both of which are incorporated herein by reference and to which priority is claimed pursuant to 35 USC 119 and 120. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of medical devices for treating scoliosis and methods of treatment using such medical devices, or methods of using such devices. 
     2. Description of the Prior Art 
     Adolescent (also called idiopathic) scoliosis is believed to be the direct result of a tight ligamentum flavum during rapid growth. The ligamentum flavum is a strong discontinuous (or segmental) ligament full of elastic fibers (which gives it its yellow color) that runs along the posterior aspect of the spinal canal. The posterior aspect of the dura, at any given spinal level, touches lamina for one third of its length, and ligamentum for the other two thirds. In the lumbar spine it acts as the center of rotation (and maybe the center of rotation for the thoracic as well, which would help explain the limited rotation available in the thoracic spine). 
     If indeed scoliosis is the result of a tight ligamentum flavum, then correction of scoliosis should be achievable by mechanical stretching. Rapid correction of a scoliotic curve is now possible because great force through multiple points of solid fixation are now available. These methods still, however, are described as steps toward inserting instrumentation for a fusion of vertebrae. A slower and steady stretch over time, would be much less violent, and would allow the use of much less force and fewer points of fixation. 
     What is needed is some kind of device and mechanics to perform the needed mechanical stretching. 
     BRIEF SUMMARY OF THE INVENTION 
     The illustrated embodiment of the invention includes a method for correction of a scoliotic curve in a spine comprising the steps of implanting an expanding rod isolated completely under the skin and attached to selected portions of the scoliotic curve of the spine at opposing ends of the rod; and producing a controlled force by means of expansion of the rod over at an extended time period under external control until a desire spinal curve is obtained. 
     The step of producing a controlled force comprises the step of generating an incremental force to stretch the scoliotic curve of the spine between the selected portions where attachment of the rod is defined. The step of generating an incremental force to stretch the scoliotic curve of the spine comprises the step of generating a force using a curved rod in a direction tending to align with the spine at the selected portions where attachment of the rod is defined. 
     The step of implanting the expanding rod comprises implanting the expanding rod posteriorly to the spine. 
     The step of producing a controlled force by means of expansion of the rod over at an extended time period comprises the step of producing the controlled force at a predetermined level over time without any combination with fusion of vertebrae. 
     The step of producing the controlled force by means of expansion of the rod over at an extended time period comprises producing the controlled force steadily for at least one month or alternatively 1-3 months. 
     The step of producing the controlled force by means of expansion of the rod over at an extended time period comprises the step of producing the controlled force steadily for such period of time as is sufficient to stretch the ligamentum flavum of the spine enough to allow the spine to straighten. 
     The invention further contemplates repeating the steps of implanting an expanding rod with multiple rods, where each rod is associated with a different scoliotic curve of the spine or a different portion of the scoliotic curve of the spine, and separately producing a controlled force by means of expansion of each corresponding rod over at a corresponding extended time period. 
     The step of producing the controlled force by means of expansion of the rod comprises the step of producing the controlled force by means of a ratcheted longitudinal extension of the rod powered by an energy sources biologically isolated from the rod by a skin barrier. 
     The invention also comprises an apparatus used for performing each of the above embodiments of the illustrated method. The invention thus includes among other embodiments a kit of a plurality of expanding rods with multiple rods, each rod being associated with a different scoliotic curve of the spine or a different portion of the scoliotic curve of the spine and separately producing a controlled force by means of expansion of each corresponding rod over at a corresponding extended time period. 
     The means for producing the controlled force by means of expansion of the rod comprises means for producing the controlled force by a ratcheted longitudinal extension of the rod powered by an energy sources biologically isolated from the rod by a skin barrier. 
     Stated in an alternative form, the invention includes embodiments where the invention is an apparatus for correction of a scoliotic curve in a spine comprising an expanding rod isolated completely under the skin; attachment screws to couple the rod to the spine at opposing ends of the rod; and a source of controlled force coupled to the rod to longitudinal extend the rod over an extended defined period of time under external control until a desire spinal curve is obtained. 
     The rod comprises a pair of telescopically coupled sleeves; and means to prevent relative rotation of the sleeves. The apparatus is combined with an external source of power, and in one embodiment the source of the controlled force comprises a torsion spring coupled to a second one of the pair of sleeves, a torsion motor coupled to the spring for torsioning the torsion spring, a power pick up electrically coupled to the torsion motor for powering the motor from the external source of power, a ratchet and a screw drive coupled to the ratchet at one end and to a first one of the pair of sleeves at an opposing end, so that a force applied to the screw drive from the torsion motor to the first one of the pair of sleeves over time longitudinally expands the collective length of the pair of sleeves. In the illustrated embodiment the torsion motor comprises a muscle wire. 
     More generally, where the invention is characterized as a combination of an expanding rod, attachment screws, a source of controlled force, and a ratchet, where the source of controlled force produces a force over a defined period of time, which force is continually maintained to some degree by the ratchet after initial generation by the source until the spine to which the force is steadily applied straightens at least to a partial degree. 
     While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side perspective view of a telescoping rod of the invention showing the telescopic sleeves. 
         FIG. 2  is a side perspective view of a drive unit of the illustrated embodiment of the invention included in the rod of  FIG. 1 . 
         FIG. 2   a  is a side perspective transparent view of the invention as depicted in  FIGS. 1 and 2  shown in assembled form. 
         FIG. 3  is a posterior view, moving from the left to the right of the drawing, of a straight, lateral bending and sciolotic spine respectively. 
         FIG. 4  is a posterior view of the rod of the invention as implanted next to a bent sciolotic spine in the left most depiction and next to a straightened spine in the right most depiction of the drawing. 
         FIG. 5  is a side perspective view of a pair of pedicle screws showing a rotational coupling to the end of the rod of the invention. 
     
    
    
     The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention comprises a rod, generally denoted by reference numeral  10 , for the treatment of scoliosis by slow stretching of selected biological tissues, for example, a selected portion of the spine, which is implantable into the body and is under external control. The invention allows for surgical treatment of the spine without fusion of any of the vertebrae, and can be used not only for scoliosis, but also in pediatric orthopedics such as for leg or limb lengthening. 
     For the purposes of the illustrated disclosure, it is assumed that adolescent (also called idiopathic) scoliosis is the direct result of a tight ligamentum flavum during rapid growth. The evidence for this assumption is impressive and overwhelming. The second assumption made in the illustrated disclosure for the sake of simplicity is that we are treating a simple, single curve, although the indications and complexities of extending the use of the invention to more complex curves is explicitly within the scope of the invention. Where multiple rods  10  are implanted each rod  10  may be fixed across a different scoliotic curve where multiple scoliotic curves exist, or may be fixed across different portions of a single scoliotic curve. In such a case, each one of the multiple rods can be separately controlled to produce the needed straightening force or expansion. 
     The proposed device comprises an expanding or telescopic rod  10  as shown in side perspective view in  FIG. 1 . As described below, the opposing ends of rod  10  will be fixed to selected positions on the spine using conventional surgical screws. The rod  10  must produce a controlled force, slowly over time, under precise external control, and be isolated or implanted completely under the skin and protected by the natural barrier, which the skin provides. Rod  10  also needs to be small, powerful, simple enough to be readily manufactured, immune to accidental activation, and biologically inert. Rod  10  of the illustrated embodiment meets each and all of these criteria. 
     The rod  10  can be as small as ½″ (2.54 cm) in diameter and typically can be made much smaller, subject only material limitations arising from the strength of the rod  10  itself. Rod  10  is can be made from any bioengineered or biological inert material desired, and in the illustrated embodiment is fabricated from metal, such as surgical quality stainless steel. Rod  10  is comprised of an inner hollow cylindrical sleeve  14  telescopically disposed in outer, hollow cylindrical sleeve  16 . The outer diameter of cylindrical sleeve  14  is chosen to telescopically slide without binding in the inner diameter of cylindrical sleeve  16  along their common longitudinal axes. A pin  12  is fixed to cylindrical sleeve  14  and extends radially therefrom through a longitudinal slot  18  defined through the wall of cylindrical sleeve  16  to stop rotation of cylindrical sleeve  14  relative to cylindrical sleeve  16  while allowing free relative longitudinal movement of cylindrical sleeve  14  relative to cylindrical sleeve  16  at least to the extent of the length of slot  18 . Sleeves  14  and  16  are shown as circular cylinders in the illustrated embodiment, but pin  12  may be removed and elliptically or other prismatic shapes may be used in place of a cylindrical shape, which would equivalently stop or limit their relative rotation to each other. Therefore, the hollow outer sleeve  16  and inner sleeve  14  are configured to limit rotational movement between the hollow outer sleeve  16  and inner sleeve  14 . When in the specification the term, “sleeve” is used without modification, it should be understood to have a general prismatic shape. 
     The larger cylindrical sleeve  16  is internally threaded. The small longitudinally extending post  20  on the right end  22  of the smaller cylindrical sleeve  14  as seen in  FIG. 1  is where the drive unit, generally denoted by reference numeral  24 , attaches as described below. Drive unit  24  as shown in the side perspective view of  FIG. 2  is housed or disposed inside the cylindrical sleeve  16  with the left end  40  of a torsion spring  26  disposed within and affixed to sleeve  14  as shown in  FIG. 2   a . The opposing end  42  of torsion spring  26  is coupled to or bears against a segment end  44  of shell  36 . Shell  36  is disposed in sleeve  16  as shown in  FIG. 2   a  and rotates within the end of sleeve  14 , but is held by a stop(s)  37  from telescopically sliding into sleeve  14 . Shell  36  is thus longitudinally fixed relative to sleeve  14 , but is free to rotate relative to sleeve  14  at least through a defined angular range. Thus, as shell  36  is rotated as described below, torsion spring  26  which has on end connected to sleeve  14  and the other end to shell  36  will wind up or down depending on the sense of rotation of shell  36 . 
       FIG. 2  shows the drive unit in exploded view which is comprised of spring  26 , motor  28 , pickup coil  30 , ratchet  32  and screw drive  34 . These elements represent the simplest configuration for the drive unit  24 , although it must be understood that any drive unit now known or later devised capable of providing the same or similar force as the illustrated drive unit  24  can be equivalently substituted without departing from the illustrated embodiment of the invention. Because of energy transfer considerations relating to coil  30  and wire  38 , additional electronic or electrical components may be required as discussed below. 
     The motor  28  comprises a muscle wire  38  wound onto a cylindrical shell  36 . Muscle wire  38  is well known to the art and is also called nitinol wire. When current is passed through the wire  38 , it heats and contracts. Wire  38  is electrically connected to or in circuit with coil  30  in which a current is inductively generated. One end  48  of wire  38  is coupled or connected to shell  36 . The opposing end  46  of wire  38  is coupled or connected to sleeve  14  at post  20  as shown in  FIG. 2   a . The contraction of wire  38  causes the entire remaining portion of drive unit  24  to rotate against the spring  26 . In other words, as wire  38  ohmicly heats due to the current supplied to it from coil  30  and its length contracts, wire  38  will cause shell  36  to rotate. Shell  36  is rotationally coupled or connected to ratchet  32 , which rotates with shell  36  in both senses of rotation. Ratchet  32  is coupled to screw drive  34  through a conventional ratcheting mechanism (not shown) thereby causing screw drive  34  to rotate in one sense of rotation, but slipping with respect to screw drive  34  in the opposite sense of direction. Thus, the screw drive  34  is rotated within sleeve  16  and driven forward or to the left in  FIG. 1  causing sleeve  14  to telescope out of sleeve  16 . The combined length of sleeves  14  and  16  thus increases. When the wire  38  cools there is no further torque applied to shell  36  by wire  38 , and torsion spring  26  will rotate shell  36  back to its original angular position within drive unit  24 . Grooves are cut into the screw threads to resist rotation of screw drive  34  in the opposite direction thereby insuring that ratchet  32  slips against the screw drive  34  when shell  3  is returned to its original angular orientation. Screw drive  34  remains in a new advanced longitudinal position within sleeve  16 . In this manner rod  10  can be repeatedly incrementally lengthened by repeated heat cycling of motor  28 . Rod  10  can only lengthen and the ratcheting action of ratchet  32  prevents it from shortening. The ratchet  32  is designed to release or disengage from screw drive  34  when a screw-driver or Allen wrench is placed into through-hex socket  50  of screw drive  34  during surgical placement and adjustment. Torsion spring  26  also provides some longitudinal compressive force which tends to urge ratchet  32  against screw drive  34 , but placement of a tool through socket  50  allows ratchet  32  to be backed off and to disengage from screw  32 . Withdrawal of the tool then allows spring  26  to urge ratchet  32  back into engagement with screw drive  34 . The initial length of rod  10  can thus be manually adjusted up or down at the time of its initial surgical implantation. 
     The pick-up coil  30  receives energy from an external hand-held source of energy (not shown), such as a low frequency generator of electromagnetic radiation, which is brought into proximity with coil  30 . Rod  10  is implanted beneath the skin barrier, while the source of energy is exterior to the body. The external inductive power source may be driven at conventional line frequency. In the event that the coil  30  is be able to efficiently drive the muscle wire  38 , then either a storage capacitor with a control diode can be added in circuit with coil  30 , or with more complexity, a battery with a diode voltage multiplier, and control diode could be used. Any means of impedance matching between coil  30  and wire  38  on one hand and between coil  30  and the inductive power source on the other may be employed. The use of external power sources and inductively powered implanted coils is well known to the art and are routinely used, for example, in charging implanted pacemaker devices. 
     For a first alternative, energy would be fed into the pick-up coil until enough was stored in the capacitor to drive the motor  28 . Upon the firing of the motor  28  the hand-held device would sense the discharge, and shut-off for the prescribed lock-out period. 
     The second alternative is the same, except that an on-board battery assists in charging the capacitor, and thus requires significantly more control electronics. 
     Consider now the surgical implantation of rod  10  and its operation within the body. Two pedicle screws  52  as shown in  FIG. 5  are placed at the top and two pedicle screws  52  at the bottom of the curve in a spine which being treated. Fixed head screws (not shown) are used. The expandable rod  10  is run above the fascia and beneath the skin between the two constructs. The rod  10  is then expanded daily typically for 2-3 months. The duration of treatment is variable and is determined according to medical considerations, which are not directly relevant here. After the desired curve in the spine is attained, the screws  52  and rod  10  are removed. 
       FIG. 3  shows moving from left to right in the drawing a posterior view of a normal straight, normal in lateral bending, and a scoliotic spine. Note that with normal lateral bending as shown in the center there is no significant rotation. Indeed, in scoliosis as shown in the right most depiction as in lateral bending there is no significant increase in rotation. This is because scoliosis is caused by a tight ligamentum flavum. Because of this scoliosis patients have loss of kyphosis or are even lordotic, even in the thoracic spine. These facts can make a slight curve in the expanding rod  10  very useful as shown in the left most depiction in  FIG. 4 . As the spine straightens, rod  10  is also flexible enough to slowly straighten with the spine as shown in the right most depiction in  FIG. 4 . 
       FIG. 4  shows the initial rod placement in the left most drawing. As the rod  10  expands, the spine has nowhere to go except to have the pedicle screws  52  cut out or for the spine to straighten. Because the expansion is slow, the pedicle screws  52  don&#39;t cut out. As the spine straightens, and also because the rod  10  is posterior to the ligamentum flavum and is in a poor position to stretch the anterior longitudinal ligament, the spine will be pushed from a horizontal into a vertical position, thus restoring normal kyphosis. 
     In order to allow both rotation, and some play for the re-establishment of kyphosis, the rod-to-pedicle screw articulation is provided as shown in  FIG. 5 . Rod  10  is coupled to pedicle screws  52  by means of a pin  54  fixed to screws  52 . The extend end  58  of pin  54  is tapered and is disposed into a conical socket  56  defined into the adjacent end  60  of rod  10 . This allows rod  10  to swivel around the pivot provided between the socket-to-pin connection to rod  10  by fixed pin  54  and pedicle screws  52 . 
     Scoliosis can be treated without difficult, conspicuous, (and ineffective) bracing; and without fusion. The key is to stretch out the ligamentum flavum. The proposed device discussed should be effective in stretching the spine out of scoliosis. This device would also have several applications other than the spine. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following invention and its various embodiments. 
     For example, while a cycling rotational motor  28  with a rotary ratchet has been described, it is entirely within the scope of the invention that a cycled linear motor in combination with a linear ratcheting mechanism could be substituted to replace the illustrated embodiment. 
     Further, while an ohmicly heated motor is the preferred embodiment, it is also possible to conceive of use of a thermally or otherwise powered piston motor where the driving fluid may be heated by RF diathermy or ultrasound energy. 
     Still further the motor may be a rotary motor or linear motor with the propelling element of the motor is magnetically coupled to a moving magnetic field source and is combined through appropriate gearing to a ratcheting mechanism which telescopes rod  10 . 
     Any means by which energy from an external source can be coupled into a motor which will mechanically telescope rod  10  is included within the spirit and scope of the invention. 
     Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations. A teaching that two elements are combined in a claimed combination is further to be understood as also allowing for a claimed combination in which the two elements are not combined with each other, but may be used alone or combined in other combinations. The excision of any disclosed element of the invention is explicitly contemplated as within the scope of the invention. 
     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself. 
     The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. 
     The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.