Surgery – Instruments – Orthopedic instrumentation
Reissue Patent
2000-01-20
2001-05-01
Buiz, Michael (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S075000, C623S017120
Reissue Patent
active
RE037161
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a spinal instrumentation system utilizing elongated members extending along the length of the spine and attached to multiple vertebrae by fixation elements, such as bone screws. In particular, the invention concerns anterior instrumentation, together with a surgical technique for implanting the instrumentation. The invention also contemplates a surgical revision technique for this spinal instrumentation.
Historically, correction of spinal disorders and treatment of spinal injuries was approached posteriorly, or namely from the back of the patient. Initially, the anterior approach to spinal instrumentation, that is from the front and side of the patient, was not favored, due to the unfamiliarity of this approach to spinal surgeons and due to the fear of severe complications, such as neurovascular injury or compromise of the spinal cord. However, in the face of some reported difficulties in addressing correction of thoracolumbar and lumbar scoliotic curvatures from a posterior approach, surgeons sought anterior forms of correction and stabilization. One such technique was developed by Dwyer in Australia during the 1960's in which a staple-screw construct was applied to the convex side of the scoliotic curvature. The screws were connected by a cable and correction was obtained by applying compressive forces at each instrumented level. The anterior spinal compression produced tensile forces within the cable which in turn generated a corrective bending moment at each of the vertebral levels.
On the heels of Dwyer's success, other anterior instrumentation followed. Further, surgeons began to recognize that certain spinal treatments were best approached anteriorly, rather than posteriorly. Anterior approaches give direct access to the intervertebral disc space for anterior release and interbody fusion. Presently, common indications for anterior instrumentation include: lumbar scoliosis with deficient posterior elements; thoracolumbar curves with extreme lordosis; paralytic thoracolumbar scoliosis requiring both an anterior and a posterior fusion; thoracolumbar spine trauma, such as burst fractures; and degenerative conditions of the vertebral body. In the case of burst fractures, it is known that neurocompression occurs from the anterior direction. Further, anterior debridement of fracture fragments is frequently believed to be a more effective means to decompress the spinal canal, as opposed to known posterior techniques.
Since the initial Dwyer instrumentation, many anterior plate and rod systems have been developed, such as the systems of Dunn, Kostuik-Harrington, Zielke and Kaneda. Many of these systems permit dynamic distraction of the vertebrae followed by direct compression of implanted bone graft contained within the resected disc space and after decompression of the neural elements.
Many of these anterior systems can lead to complications. Some of the more prominent problems that have occurred involve failure of the fixation components, and an often high incidence of loss of reduction or correction. Many of the difficulties in this respect can be traced to the vertebrae instrumented at the end of the construct where the loads on the instrumentation are the greatest. In some cases, bicortical purchase of vertebral body screws has been found to assure a more solid fixation at the ends of the construct and to protect against dislodgement of the screws. There does, however, still remain a need for an anterior instrumentation that can provide adequate correction of spinal deformities and that can be easily implanted. In addition, the system must ensure a strong fixation that will not deteriorate over time resulting in a loss of correction.
In some cases, it has been found that revision surgery is necessary, even when following the best possible surgical implantation of the instrumentation. Frequent indications for revision of spinal instrumentation include extension of existing instrumentation, and replacement of failed implants. In the cases involving early spinal implants, revision required cutting away the spinal implants. As implant design became more sophisticated, capabilities were developed for revision surgery that was relatively safe to the patient and non-destructive to implants, particularly those implants that were intended to be retained.
In systems using bone screws, revision surgeries can significantly compromise the vertebral body. In addition, in certain anterior approaches where stronger fixation is essential, revision procedures to replace failed components may necessarily compromise the new construct.
In view of these difficulties, there is a need for a spinal fixation system that is readily suited for revision surgery. Specifically, the system must be suitable for the addition or removal of components by way of revision without sacrificing either an existing construct or eliminating the possibility of implanting a new, more stale construct. In addition, there is a need for revision techniques that permit complete removal of a construct once fusion has occurred, again without compromising the spine or the implants.
SUMMARY OF THE INVENTION
To address these needs, the present invention contemplates a method for anterior fixation of the spine commencing with a thoracoabdominal exposure of the spinal segments to be instrumented. In the preferred embodiment, fusion devices are implanted within the cephalad and caudal disc spaces after a total discectomy. The fusion devices are configured to contain bone growth material to promote bone ingrowth and consequently fusion of the instrumented disc spaces. These cephalad and caudal fusion devices serve as anchors to ensure a stable and solid anterior construct.
In accordance with the method, bone screws are engaged within the vertebral bodies of the intermediate vertebrae. Preferably, the bone screws are variable angle screws having a cancellous threaded portion that is long enough to engage both lateral cortices of the respective vertebrae. An attachment member is provided having a head portion configured substantially similar to the head portion of the variable angle screw. In the preferred embodiment, eyebolt assemblies are used to attach and fix the head portions of the variable angle screws and the attachment members to an elongated spinal rod. The rod is positioned posteriorly of the head portions and is offset from the longitudinal axis of the fusion implant. It has been found that this anterior system and surgical technique provides a more reliable and complete decompression of the spinal canal. The use of the fusion devices as anchors at the ends of the construct renders this anterior instrumentation a viable alternative to address spinal conditions previously reserved for treatment from a posterior approach.
The system in accordance with one embodiment utilizes a threaded cylindrical fusion implant that is placed between or threaded into the endplates of the adjacent vertebrae. The implant can be filled with morcellized autologous bone to promote fusion through the implant and between the vertebral endplates. One end of the fusion implant is laterally disposed and accessible for placement of an attachment member. In one embodiment, the exposed end has a threaded opening for receiving a threaded post of the attachment member. In accordance with one feature of the present invention, the attachment member also includes a head portion that is configured substantially similar to the head of the bone screw engaged in the intermediate vertebrae. The head portion defines a slot for receiving the body of an eyebolt assembly, and includes a pattern of radial serrations. The head portions of the fusion implant attachment members and the bone screws are engaged to the spinal rod by a variable angle connection member comprising an eyebolt, nut and splined washer. The attachment member provides a significant benefit in that it adapts a known fusion implant to appear and behave as a bone screw with enhanced rigidity and fixation.
In another aspect of the in
Boyd Lawrence M.
Michelson Gary K.
Buiz Michael
Martin & Ferraro LLP
Michelson Gary Karlin
Reip David O.
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