Abstract
A spinal implant for limiting flexion of the spine includes a tether structure for encircling adjacent spinal processes. Usually, a pair of compliance members will be provided as part of the tether structure for elastically limiting flexion while permitting an extension. A cross-member is provided between the compliance member or other portions of the tether structure to stabilize the tether structure and prevent misalignment after implantation.
Claims
1. A spinal implant for restricting flexion in a spine, said spinal implant comprising: a tether structure comprising an upper strap, a lower strap, and a compliance member coupling the upper strap to the lower strap, wherein the tether structured is configured to encircle at least two spinous processes of the spine, and wherein the compliance member elastically elongates to apply a force on the spinous processes to resist flexion of the spine.
2. A method for restricting flexion in a spine, said method comprising: providing a tether structure comprising an upper strap, a lower strap, and a compliance member coupling the upper strap to the lower strap; encircling at least two spinous processes of the spine with the tether structure; and resisting flexion of the at least two spinous processes.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:
[0029] FIG. 1 is a schematic diagram illustrating the lumbar region of the spine including the spinal processes (SP), facet joints (FJ), lamina (L), transverse processes (TP), and sacrum (S).
[0030] FIG. 2 illustrates a spinal implant of the type described in US 2005/0216017A1.
[0031] FIGS. 3 and 4 illustrate how the spinal implant of FIG. 2 can become misaligned over time.
[0032] FIG. 5 illustrates a first embodiment of a spinal implant having a cross-member in accordance with the principles of the present invention.
[0033] FIGS. 6A and 6B illustrate the spinal implant of FIG. 5 having a rigid cross-member.
[0034] FIGS. 7A and 7B illustrate the spinal implant of FIG. 5 having a semi-rigid cross-member.
[0035] FIGS. 8A and 8B illustrate the cross-member of FIG. 5 having an elastic cross-member.
[0036] FIG. 9 illustrates a specific embodiment of a cross-member useful in the apparatus and methods of the present invention.
[0037] FIG. 10 illustrates the cross-member of FIG. 9 in an implant.
[0038] FIG. 11 illustrates an embodiment of the present invention having a pair of cross-members.
[0039] FIG. 12 illustrates the spinal implant of FIG. 11 in an implant.
[0040] FIG. 13 illustrates an additional continuous tether structure over a spinous process on another pair of adjacent vertebrae.
[0041] FIG. 14A and 14B illustrate use of a reinforcement member on a single connector which does not include a compliance member, while FIGS. 15A and 15B illustrate use of a reinforcement member on a single connector which includes a compliance member.
DETAILED DESCRIPTION OF THE INVENTION
[0042] Referring now to FIG. 5, a spinal implant 20 constructed in accordance with the principles of the present invention comprises an upper strap 22, a lower strap 24, and a pair of compliance members 26 joining the upper and lower straps. Typically, the upper and lower straps 22 and 24 will be non-distensible but will be joined to the compliance members 26 so that they can be expanded from a constricted configuration, as shown in broken line, when the patient's spine is in a neutral position between flexion and extension, to an expanded configuration (shown in full line) when the patient's spine is in flexion. The compliance members 26 will provide a force which acts against the extension of the spinous processes, as generally described in prior patent application U.S. 2005/0216017, which has been previously incorporated herein by reference. In particular accordance with the present invention, a cross-member 30 extends between and joins the compliance members 26. The cross-member 30 passes through the interspinous ligament ISL.
[0043] As shown in FIGS. 6A and 6B, the cross-member 30 may be rigid and be rigidly attached to the compliance members 26 in a generally H-shaped configuration so that the compliance members do not shift relative to each other even when the upper and lower bands 22 and 24 are pulled apart, as shown in FIG. 6B. Alternatively, the cross-member 30 may be semi-rigid (or semi-compliant) so that it will undergo compression when the upper band 22 is pulled away from the lower band 24, as shown in FIG. 7B. In a third embodiment, the cross-member 30 may be entirely elastic, as shown in FIGS. 8A and 8B. In such instances, the cross-member 30 will allow the compliance members 26 to vertically displaced relative to each other by a controlled amount, as shown in FIG. 8B.
[0044] FIG. 9 illustrates an exemplary cross-member 50 which can be coupled to compliance members 26, as shown in FIG. 10. The cross-member 50 is a rigid structure which may be attached (and optionally detached) from the compliance member during implantation of the spinal implant. End portions 52 of the cross-member are shaped and adapted to be attached to the cylindrical bodies of the compliance members. Other shapes and structures for selective attachment and detachment of the cross-member are, of course, readily available.
[0045] A pair of cross-members 60 are illustrated in FIG. 11. The cross-members 60 have endpieces 62, each having a slot 64 which receives the corresponding band 22 or 24. Cross-members 60 can thus be disposed directly over the upper and lower surfaces of the compliance members 26, as shown in FIG. 12. Usually, cross-members 60 will themselves be compliant in order to avoid inhibiting of extension of the spinal processes SP4 and SP5, as shown in broken line in FIG. 12. FIG. 13 illustrates positioning at least one additional continuous tether structure over a spinous process on another pair of adjacent vertebrae, and mechanically coupling opposed portions of the at least one additional tether structure through the interspinous space.
[0046] Referring now to FIG. 14, yet another spinous process constraint system 1460 comprises first and second hook-like attachment members 1462 and 1464. The hook members 1462 and 1464 are connected in a C-shaped pattern, as shown in FIG. 14.
[0047] The spinous process constraint 1460 of FIG. 14 will have a tendency to deform when placed under an axial load as the spinous processes undergo a flexion causing movement in the direction of arrow 1465. Typically, a region 1466 of the constraint will tend to bow inwardly which causes the superior and inferior hook members 1462 and 1464 to displace laterally, increasing the risk that they will shift from their intended positions on the spinous processes. In order to alleviate this condition, a reinforcement member 1467 can be placed over a portion of the single connector 1463 between the hooks 1462 and 1464. The reinforcement member may be a simple sleeve constructed from a relatively rigid material, such as a metal or rigid polymer, having a central passage which is placed over the single connector. Other reinforcement structures would also be possible. Additionally, the sleeve embodiment shown in FIG. 14B could be modified to be used with constraint embodiments including compliance members as described elsewhere in this application.
[0048] Similarly, as shown in FIG. 15, a spinous process constraint system 1570 comprises first and second hook-like attachment members 1572 and 1574 arranged in C-shaped pattern, generally as shown in FIG. 14, and further comprises compliance member 1578 attached to superior and inferior segments of the single connector 1576 (which is preferably non-compliant).
[0049] The spinous process constraint 1570 of FIG. 15 can also undergo deformation when subjected to an axial load, as shown in FIG. 15A. A reinforcement assembly 1573 specifically adapted for constraints having compliance members 1578 is illustrated in FIG. 15B. The reinforcement assembly 1573 connects to a superior segment 1575 of the single connector 1576 and includes a slide rod 1571 extending toward an inferior segment 1577 of the single connector 1576. The slide rod 1571 is received in a bearing structure 1579 attached to the interior segment 1577 which allows the rod to translate as the segments 1573 and 1577 move toward and away from each other as the spine undergoes extension and flexion. The reinforcement assembly 1571 helps maintain the proper alignment between the superior and inferior segments 1575 and 1577 to prevent the bowing and deformation illustrated in FIG. 15A
[0050] Further details and alternative embodiments of flexion limiting devices, their use, and associated instruments are disclosed in the patent applications previously incorporated herein by reference.
[0051] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
