Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-08-28
2004-04-20
O'Connor, Cary E. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C623S017160, C606S075000
Reexamination Certificate
active
06723096
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to surgical procedures for spinal stabilization, and more specifically to instrumentation and techniques for inserting a spinal implant within the intervertebral disc-space between adjacent vertebra. More particularly, while aspects of the present invention may have other applications, the invention provides instruments, techniques, and implants especially suited for implanting one or more fusion cages in an unreamed disc space.
There have been an extensive number of attempts to develop an exceptional intradiscal implant that could be used to maintain the height and stability of the disc interspace between adjacent vertebra, at least until complete arthrodesis is achieved. These “interbody fusion devices” have taken many forms. For example, one of the more prevalent designs takes the form of a cylindrical implant. These types of implants are presented in patents to Bagby, U.S. Pat. No. 4,501,269; Brantigan, U.S. Pat. No. 4,878,915; Ray, U.S. Patent Nos. 4,961,740 and 5,055,104; and Michelson, U.S. Pat. No. 5,015,247. In the cylindrical implants, the exterior portion of the cylinder can be threaded to facilitate insertion of the interbody fusion device, as represented by the Ray, Brantigan and Michelson patents. In the alternative, some of the fusion implants are designed to be driven into the intradiscal space with little or no rotation. For example, this type of device is represented in the patent to Brantigan. A combination implant having the ability for threaded insertion or push-in insertion is disclosed in U.S. Pat. No. 5,782,919 to Zdeblick et al.
U.S. Pat. No. 5,484,437 to Michelson discloses a technique and associated instrumentation for inserting a fusion device. As described in more detail in the '437 patent, the surgical technique involves the use of a distractor having a penetrating portion that urges the vertebral bodies apart and a hollow sleeve having teeth at one end that are driven into the vertebrae adjacent the disc space created by the distractor. These teeth engage the vertebra to maintain the disc space height during subsequent steps of the procedure following removal of the distractor. In accordance with one aspect of the '437 patent, a drill is passed through the hollow sleeve to remove portions of the disc material and vertebral bone in order to ream the disc space and reduce the endplates to bleeding to produce a prepared bore for insertion of the fusion device. The drill is then removed from the sleeve and a fusion device having a diameter greater than the height of the disc space is positioned within the disc space using an insertion tool.
The device depicted in the Michelson patent is representative of this type of hollow implant which is typically filled with a bone growth inducing substance to promote bone growth into and through the device. This implant includes a plurality of circular apertures which communicate with the hollow interior of the implant, thereby providing a path for tissue growth between the vertebral end plates and the bone growth material within the implant.
One problem that is not adequately addressed by the above prior devices concerns restoring and maintaining the normal anatomy of the fused spinal segment. Naturally, once the disc is removed, the normal lordotic or kyphotic curvature of the spine may be altered. In response to this problem, the adjacent vertebral bodies may be reamed with a cylindrical reamer that fits the particular shape of the implant. In some cases, distraction techniques are used to establish the normal curvature prior to reaming. However, for a cylindrical implant, the over-reaming of the posterior portion is generally not well accepted because of the extensive removal of load bearing bone of the vertebrae. Over time, the implant tends to migrate into the vertebral bodies since the load-bearing surfaces of the endplates are no longer adequate for the implant to support the spinal column loads. This migration is often referred to as subsidence. When an implant subsides into adjacent bone, the disc space can collapse, resulting in potentially adverse consequences to the patient's health.
Another problem is that when the disc space and adjacent endplates are reamed, the implant must have a height greater than that of the original disc space height to restore the disc space to its normal anatomy. When large implants are bi-laterally inserted in the disc space, the lateral spacing and separation between the implants that can be attained is less than that attainable with smaller implants used in the same disc space. This positions the larger implants closer to the medial portion of the disc space and vertebral endplates, thus increasing the risk of migration into the vertebral bodies and subsidence of the spinal column around the implant. Also, lateral stability of the spinal column is reduced since less support is provided at the hardy bony peripheral ring of the adjacent vertebral bodies. Thus, it is desirable to maintain proper lateral separation of the implants in the disc space so that each implant is bearing on the strongest portion of the vertebral bodies and the lateral stability of the spinal column is maintained.
While the more recent techniques and instrumentation represent an advance over earlier surgical procedures for the preparation of the disc space and insertion of the fusion device, the need for improvement still remains. There remains a need for interbody fusion cages that may be inserted into an unreamed disc space, as well as instruments and techniques for inserting these fusion cages in an unreamed disc space to stabilize the spine. The present invention is directed to these needs and provides convenient methods, instruments, and implants for effective preparation of an unreamed disc space in conjunction with implant placement.
SUMMARY OF THE INVENTION
One object of the present invention is to provide instruments permitting placement of a fusion cage in an unreamed disc space. One instrument of the present invention includes a first distractor and a second distractor configured to be inserted in side-by-side relation in the disc space. At least one distractor has a guide surface abutting the other distractor to maintain the distractor spacing as the distractor pair is inserted into the disc space. In a preferred form, the guide surface is offset from the central axis of the instrument.
In one specific embodiment, each distractor has a body portion with a leading end and a trailing end. The body portions distract the disc space and form a channel therethrough as the distractors are inserted. Preferably, at least one of the distractors is provided with a medially extending portion extending from the body portion towards medial area of the disc space. The guide surface is formed by a medial side of the medially extending portion. The medially extending portion can be provided with a height less than that of the body portion. The guide surface of the medially extending portion guides the insertion of a cage into the distraction channel formed through the unreamed disc space remaining after withdrawal of the other distractor.
In another instrument of the present invention, first and second distractors are provided with first and second central spacers. Each central spacer has a width between its guide surface and the body portion of the distractor from which it extends. The central spacers extend medially from the body portion into the disc space so that the guide surfaces are adjacent one another. In one form, the first central spacer has a width that is greater than the width of the second central spacer. The guide surfaces maintain the spacing between the body portions as the first and second distractors are inserted into the disc space. Alternatively, the central spacers are provided with an equal width. In another form, the first and second distractors each further include a lateral spacer having a width that tapers from a maximum width at the trailing end of the body portion to a minimum width at the d
Burkus J. Kenneth
Dorchak John D.
Ray, III Eddie F.
White John L.
Melson Candice C.
O'Connor Cary E.
SDGI Holdings Inc.
Woodard Emhardt Moriarty McNett & Henry LLP
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