Telescoping Spinal Fixator

The present invention is directed to a telescoping spinal fixator adapted for placement between respective spinal vertebrae especially to relieve compression on the spinal cord during spinal fusion or other spinal prosthetic procedure. The spinal fixator of the invention is particularly characterized by being expandable once it is inserted in position between respective vertebrae on either side of an excised vertebrae and by having the two ends of the spinal fixator actually disposed within cavities in the vertebrae to prevent lateral movement and disengagement.

Various techniques have been used for many years for the surgical treatment of spinal fractures. These technique have included laminectomy and various plate and screw procedures. U.S. Pat. No. 4,401,112 to REZAIAN describes an expandable spinal fixator which is essentially a turnbuckle mounted between upper and lower bearing members, each of which essentially is a pedestal which rests on and engages the opposing surfaces of the vertebrae between which it is placed. Although, the device permits extension of the fixator once it is in place, its inherent lateral instability makes it necessary for the device to be further anchored by brackets which are stapled to the spinal vertebrae. Further, the type of turnbuckle employed in the patented device severely limits the extent of extension which is possible once the device is in place between the vertebrae. Additional extension, once the device is anchored by the supporting plates, then becomes impossible unless these plates are first disengaged from the vertebrae to which they are stapled.

Particularly in view of the dire consequences which attach to any lateral slippage or movement in spinal fixators and the need which often arises for greater expansion and separation between the vertebrae, a purpose of the present invention is to provide an improved spinal fixator which can both be securely anchored between the vertebrae so that lateral movement or slippage is virtually eliminated and which can be extended to a greater extent than has heretofore been possible using devices of the prior art and subsequently removed the following completion and recovery from prosthesis.

FIG. 1 is an exploded view of the invention illustrating its respective components.

FIG. 2 is perspective view illustrating the device of the present invention in its collapsed configuration prior to insertion between spinal vertebrae.

FIG. 3 is a perspective view of a broken spine illustrating the initial procedure for insertion of the fixator between vertebrae.

FIG. 4 is a perspective view of a broken spine illustrating the fixator of the invention in place between two vertebrae.

In accordance with the present invention a spinal fixator is provided which comprises upper and lower bearings elements for engaging respective upper and lower vertebrae within cavities that are formed in each of the vertebrae. An elongated threaded rod connects and extends between the two bearing members. Disposed coaxially intermediate the two bearings with the connecting rod is an adjustment collar which can be rotated to increase or decrease the distance between the two bearing members. A particularly unique feature of the present invention is the extent to which the entire device can be collapsed along its longitudinal axis to provide a compact unit of reduced longitudinal dimensions to facilite insertion between the respective vertebrae. This unique compactness is achieved in part by providing cavities in each of the bearing elements to accommodate a substantial portion of the adjustment collar. The device of the invention is further characterized in that the respective bearing elements are each specifically adapted to be placed within an excavated cavity in one of the opposing vertebrae between which the device of the invention is placed. This feature of the invention is especially significant for avoiding lateral displacement of the fixator and eliminating the need for external supporting brackets.

The invention will however, be more fully appreciated by having specific reference to the drawings which illustrate a preferred embodiment thereof.

Directing attention initially to FIG. 1 of the drawings, which is an exploded view of the device of the invention illustrating in detail its respective components, upper and lower bearing elements 1 and 2, which are preferably of eliptical or other non-circular cross-section to inhibit rotation within the vertebral cavity, are shown having respective hollow cavities therein, 3 and 4. Anchored to the bearing element 1 and mounted coaxially with it in cavity 4 is elongated threaded rod 5, having (in this instance) a left handed thread. Elongated adjustment collar 6 is illustrated having a hexagonal configuration to facilitate its being turned by a wrench. It will be understood that other configurations can as well be used to achieve a similar elongation. The adjustment collar 6 is provided at its upper portion with a coaxially bore having female threads which mate with the male threads of rod 5. The lower portion of adjustment collar 6 is provided with a cavity 8 of larger lateral dimensions than the bore 7. This lower cavity is also provided with female threads of opposite hand to those of the rod 5 and bore 7.

The lower bearing element 2 has disposed axially within its hollow cavity 4 a threaded tubular member 10 whose lower end engages solid base 12 and which is provided with male threads for its entire length which mate with the female threads provided in the interior cavity 8 of adjustment collar 6. The tubular member 10 has an axial bore 11 which is smooth and of sufficient lateral dimensions to permit passage through it of threaded rod 5. The smooth unthreaded bore 11 extends the entire length of the tubular member 10 and through the solid base 12 of the bearing element 2. Small holes 9 are conventionally provided in the adjustment collar 6 for insertion of locking pins, wire, or screws, to prevent any rotation of the collar once the device is in place. Advantageously, these holes traverse the corners of the collar 6, rather than extending radially to central bore 7. Similar provisions can be made in bearing elements 1 and 2 to facilitate anchoring within the vertebrae.

FIG. 2 illustrates the components shown in exploded view in FIG. 1 in compressed configuration such as is utilized during the insertion procedure contemplated in accordance with the invention. As shown, the upper and lower bearing elements 1 and 2 are aligned to one another with only sufficient space between the two elements for insertion of a wrench to permit turning of the adjustment collar 6. The threaded connecting rod 5 is joined at its upper end to the base of bearing element 1 and at its other end actually extends through the bore 11 to emerge past the bottom of solid base 12 of bearing element 2. Adjustment collar 6 is almost totally contained within the respective cavities 3 and 4 of the bearing elements except for the small portion which is exposed between the respective bearing elements to permit engagement with a wrench or other device for tuning the adjustment collar. Tubular member 10 which is mounted within the cavity 4 of bearing element 2 is otherwise disposed within the cavity 8 of adjustment collar 6 which has female threads which engage the male threads of the tubular member.

It will be appreciated that in order to permit axial displacement of the respective bearing elements 1 and 2 by turning the adjustment collar 6 it is necessary that the threads on rod 5 and their associated threaded mating surfaces be of one hand while the threads of the tubular member 10 and its associated threaded mating surfaces of the other hand. It should also be appreciated that the threads of the rod 5 be of greater pitch then those of the elongated member 10, preferably two to three times the pitch thereof.

Insertion of the device of the invention between two spinal vertebrae is illustrated in FIG. 3 of the drawings. As is commonly necessary for prosthetic implants of spinal fixators, a portion of one vertebrae disposed between vertebrae 16 and 17 of the drawings has been removed. By appropriate surgical procedure, cavities 19 and 20 have been provided opposing one another in the respective vertebrae 16 and 17. In order to achieve decompression of the spinal cord 14, the device of the invention is implanted in cavities 19 and 20 in respective vertebrae 16 and 17 adjacent excised vertebrae 18. The lower protruding end of the threaded connecting rod 5 is initially disposed within cavity 20 while the device of the invention is in its compressed or telescoped configuration as illustrated in FIG. 2 of the drawings. Upper bearing element 1 is then inserted within cavity 19 so that it rests securely within the cavity. In order to further prevent movement within the cavity appropriate surgical cement such as methyl methacrylate or fixation devices maybe employed. With the device properly aligned vertically between the respective vertebrae and with the upper bearing 1 firmly engaged within cavity 19, adjustment collar 6 is rotated in the appropriate direction to cause expansion of the device of the invention. This expansion takes place by linear displacement of bearing element 2 relative to the upper bearing 1 so that eventually the device is disposed as illustrated in FIG. 4 of the drawings. As seen in FIG. 4 of the drawings the lower bearing element 2 is firmly seated within cavity 20 in vertebrae 17 in the same manner as the upper bearing element 1 is seated in cavity 19. Adjustment collar 6 is now fully exposed and located outside of the interior portions of the respective bearing elements. As previously noted, once the device is properly implanted between the vertebrae and the desired extension has been achieved, it is desirable to place locking pins or other devices in the adjustment collar to prevent accidental rotation and compression of the device. It will be appreciated by those of ordinary skill in the art that the device of the invention can be constructed of various materials having the strength, durability and physiological acceptability required for such prosthetic implants. Typical materials can be, for examples stainless steel and titanium which may be provided with a roughened to porous surface to facilitate adhesion to the bone.

Various modifications and equivalent variations in the invention will also be apparent and are considered to fall within the scope of the invention.