Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-01-23
2003-11-18
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S075000
Reexamination Certificate
active
06648887
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of spinal implant systems, and particularly to systems that employ elongated spinal implants, such as rod and plates, connected at various locations along the spinal column. More particularly, the invention concerns a connection assembly that provides variable angle adjustability to the elongated spinal implant relative to a bone fastener engaged to the spine.
Several spinal fixation systems have been developed for use in correcting and stabilizing sections of the spinal column and facilitating spinal fusion. In one such system, a bendable elongated spinal implant, such as a rod, is longitudinally disposed adjacent the vertebral column and then secured to various vertebrae along the length of the column by way of a number of bone fasteners of fixation elements. A variety of bone fasteners can be utilized, such as hooks or bone screws, which are configured to engage specific portions of a vertebra.
An example of one such system is the TSRH® Spinal System of Sofamor Danek Group, Inc. In this system, various hooks and bone screws are engaged to a spinal rod by way of eyebolts. In early versions of the TSRH® Spinal System, the vertebral hooks and bone screws were attached to the spinal rod at a fixed orientation, usually projecting perpendicularly below the rod. At the time, the TSRH® Spinal System presented a significant advance over prior systems in its VERSATILITY, strength of fixation, and ease of implantation.
However, one drawback faced by the original TSRH® Spinal System, as well as the other prevalent fixation systems, was that the surgeon was required to make significant adjustments to the contour of the bendable rod so that the bone fasteners could solidly engage the vertebra bodies. What was needed, then, was a bone fastener that could be connected to the spinal cord a variable angle. In order to address this need, the TSRH® Variable Angle Screw was developed, as described in U.S. Pat. No. 5,261,909. This Variable Angle Screw utilized the same TSRH® eyebolt to achieve a connection to a spinal rod. In addition, the Variable Angle System incorporated a washer that fit over the eyebolt, engaged the spinal rod within a groove in one surface of the washer, and provided a radially splined surface facing the bone fastener. The bone fastener had a complementary splined surface so that the fastener could be situated at variable angular orientations relative to the spinal rod. A nut threaded onto the post of the eyebolt clamped all the components together to complete the assembly.
The Variable Angle Screw system of the '909 Patent presented a significant advance over prior rod-based implant systems. The system of the '909 Patent was relatively compact and required a minimal number of parts, yet was able to accomplish a solid fixation of the bone fasteners to the rod at a wide range of angular orientations. One drawback of the system was that the eyebolt-nut combination required side tightening of the nut to clamp the system together. This side-tightening aspect required a larger surgical site about the spine so that a wrench could be manipulated. To address this difficulty, a top-tightening assembly was developed as disclosed in U.S. Pat. No. 5,282,801. The clamp assembly depicted in the '801 Patent replaced the eyebolt and nut with a clamp body having a T-bar against which the head of the variable angle bone fastener was clamped. In addition, while the original TSRH® System relied upon tightening a nut against the variable angle bone screw, the top-tightening approach of the '801 Patent utilized a set screw that acted against the spinal rod to push the spinal rod into the interlocking washer, and ultimately against a complementary spline face of the variable angle screw. With this system, the variable angle capability was retained, while a top-tightening feature was added.
With the addition of the top-tightening capability, the more recent TSRH® Spinal System has provided surgeons with a great deal of flexibility in the placement and orientation of bone fasteners, such as hooks and screws, relative to a spinal rod. The variable angle components greatly reduce the need to manipulate and bend the spinal rod to conform to the patient's anatomy. Even with the great improvements presented by the TSRH® Spinal System, a certain amount of shaping or contouring of the spinal rod has still been required. Specifically, the rod must be shaped so that the point of attachment of the bone fastener to the rod is the same distance from the vertebral body as the splined or interdigitating portion of the bone fastener. This vertical or height adjustment is necessary so that the variable angle components are properly aligned for accurate connection when the assembly is clamped to together.
In order to address this difficulty, later systems were developed that provided for a certain degree of vertical adjustability. By vertical or height adjustability, it is meant adjustment along the length of the bone fastener. Adjustment in this dimension allows the rod to be situated at varying distances from the spine, or oriented with a pre-set contour regardless of the location of the fastener.
One approach to achieving vertical adjustability has been to adapt a Schantz-type bone fastener to the variable angle and top-tightening TSRH® System, such as described in the above-mentioned '801 Patent. A Schantz-type fastener includes an elongated smooth shank portion. Adapting this type of fastener to the TSRH® System required the addition of a split clamp that fit over the T-bar of the connector. The split clamp defined a bore to receive the shank of the Schantz-type fastener, in which the bore diameter is effectively reduced around the shank as the split clamp halves are pressed together. One of the clamp halves included an interdigitating feature to engage the variable angle washer. As with the system described in the '801, the top-tightening setscrew is tightened against the rod, which pushes the washer against the split clamp to compress the clamp halves between the washer and the T-bar.
This split clamp has allowed use of a Schantz-type bone fastener, such as a bone screw, to introduce vertical adjustability to the angular adjustability present in the TSRH® System. In addition, the split clamp can be adapted to the top-tightening aspect of the TSRH® System as reflected in the '801 Patent. One difficulty that remains is that the overall construct still embodies a certain amount of “fiddle factor”to implant and connect together. In addition, the addition of the split clamp does not reduce the overall prominence of the construct. There remains a need for a connector assembly that can accommodate a Schantz-type bone fastener while addressing the drawbacks of these prior systems.
SUMMARY OF THE INVENTION
To address this need, the present invention contemplates a connector assembly that includes a variable angle clamp configured to engage the shank of a Schantz-type bone fastener. The clamp includes a pair of clamp halves forming a slot therebetween that intersects a clamping bore configured to receive the bone fastener. Thus, the clamp can be in the form of a split clamp in which the clamp halves are compressed together to reduce the bore and provide a clamping force on the shank of the bone fastener within the bore.
In one important feature of the invention, the clamp halves define an open channel that is configured to receive the stem portion of a connector that provides a link to an elongated spinal implant, such as a spinal rod. In certain preferred embodiments, the clamp and open channel can be configured to be mounted on a variable angle top-tightening connector of the type described in U.S. Pat. No. 5,282,901. However, the clamp halves and open channel can alternatively be configured to mate with other connectors that provide a means to connect the clamp, and ultimately the bone fastener, to an elongated implant.
Each of the clamp halves includes an outer surface against which a clamping
Maginot, Moore & Bowman LLP
Philogene Pedro
Priddy Michael B.
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