ANTERIOR SPINAL INSTRUMENTATION
AND METHOD FOR IMPLANTATION AND
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, mat 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 neurooompression 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 5 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 exist10 ing 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 non15 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 20 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. 25 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 stable construct. In addition, mere is a need for revision techniques that permit 30 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 contem
35 plates 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
40 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
45 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
so 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
ss and is offset from the longitudinal axis of the fusion implant It has been found that mis 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
60 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 65 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 verte