Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-05-06
2001-06-05
Smith, Jeffrey A. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06241769
ABSTRACT:
BACKGROUND OF INVENTION
FIELD OF THE INVENTION
This invention relates generally to the treatment of injured, degenerated, or diseased tissue in the human spine, for example, intervertebral discs and vertebrae themselves. It further relates to the removal of damaged tissue and to the stabilization of the remaining spine by fusion to one another of at least two vertebrae adjacent or nearly adjacent to the space left by the surgical removal of tissue. More particularly, this invention relates to the implantation of devices which can be inserted to take the structural place of removed discs and vertebrae during healing while simultaneously sharing compressive load to facilitate bony fusion by bone growth between adjacent vertebrae to replace permanently the structural contribution of the removed tissue. This invention further relates to the implantation of devices which do not interfere with the natural lordosis of the spinal column. This invention further relates to implants which are radiolucent to permit more accurate diagnostic imaging follow up.
BACKGROUND OF THE INVENTION
For many years a treatment, often a treatment of last resort, for serious back problems has been spinal fusion surgery. Disc surgery, for example, typically requires removal of a portion or all of an intervertebral disc. The most common sites for such surgery, namely those locations where body weight most concentrates its load, are the lumbar discs in the L1-2, L2-3, L3-4, L4-5, and L5-S1 intervertebral spaces. In addition, other injuries and conditions, such as tumor of the spine, may require removal not only of the disc but of all or part of one or more vertebrae, creating an even greater need to replace the structural contribution of the removed tissue. Also, a number of degenerative diseases and other conditions such as scoliosis require correction of the relative orientation of vertebrae by surgery and fusion.
In current day practice, a surgeon will use one or more procedures currently known in the art to fuse remaining adjacent spinal vertebrae together in order to replace the structural contribution of the affected segment of the disc-vertebrae system. In general for spinal fusions a significant portion of the intervertebral disk is removed, and if necessary portions of vertebrae, and a stabilizing element, frequently including bone graft material, is packed in the intervertebral space. In parallel with the bone graft material, typically additional external stabilizing instrumentation and devices are applied, in one method a series of pedicle screws and conformable metal rods. The purpose of these devices, among other things, is to prevent shifting and impingement of the vertebrae on the spinal nerve column. These bone graft implants and pedicle screws and rods, however, often do not provide enough stability to restrict relative motion between the two vertebrae while the bone grows together to fuse the adjacent vertebrae.
Results from conventional methods of attempting spinal fusion have been distinctly mixed. For example, the posterior surgical approach to the spine has often been used in the past for conditions such as scoliosis, using Harrington rods and hooks to align and stabilize the spinal column. In recent years many surgeons have adopted anterior fusion because of the drawbacks of the posterior approach, the primary problem being that in the posterior approach the spine surgeon must navigate past the spinal column and its nerve structure. However, results of anterior surgery are variable and uncertain because constraining the vertebrae from this side does not address the loads put on the spine by hyperextension, such as from rocking the body in a backwards direction.
Pedicle screws and rods, always implanted posteriorly, tend to loosen either in the bone or at the screw-rod interface if fusion is not obtained. Fusion rates for posterolateral instrumented fusions range from 50% to 90%. It must be kept in mind that plain x-rays are only 65-70% accurate in determining fusion status and most studies use this inadequate method to determine fusion status, suggesting that the non-union rate may be greater than reported. It is also known that posterior pedicle screw systems do not prevent all motion anteriorly, leading to the risk of fatigue failure of the metal and screw breakage. This continued motion may also lead to persistent pain, despite solid posterior bony fusion, if the disc was the original pain generator. These well documented failures of pedicle screws have given rise to extensive litigation in the United States.
In contrast to the U.S. common practice of using either IBF devices, implanted from the anterior position, or pedicle screws, implanted posterior, in Europe, spine surgeons use both IBF devices and pedicle screws in combination to achieve stability of the spine. These procedures may be more successful in producing fusion but are far more invasive and costly and have higher morbidity for the patient.
More generally there is a great deal of variability in technique and uncertainty in outcome for the various methods now in use for spinal surgery. For example, Fraser, R. D. points out in “Interbody, Posterior and Combined Fusions,” Spine, V20(24S):1675, Dec. 15, 1995, “analysis of the literature does not indicate that one form of fusion is significantly better than another for degenerative conditions of the lumbar spine.” Fraser did not have the results of recent studies involving use of metal interbody cage devices. Ray, Charles D. reported the results of the original IDE study involving his Ray Threaded Fusion Cage (Ray-TFC) in Spine V22(6):667, Mar. 15, 1997. Two hundred eight patients had two year follow-up and were reported to have 96% fusion rate with only 40% excellent results and 25% fair or poor results.
There are only two published reports on the use of the BAK Threaded Interbody Fusion Cage. The first, published by Hacker, R. J., Spine V22(6):660 Mar. 15, 1997 compares posterior lumbar interbody fusion using the BAK device to anterior and posterior fusion with allograft bone. Hacker found that patient satisfaction was equivalent but overall costs were less for the BAK. Zucherman reported on the early experience with laparoscopically assisted ALIF with BAK but no outcomes data are presented on these first 17 patients. Kuslich, S. D. presented the results of the multi-center IDE study of 947 patients who had fusions using the BAK device at the 1996 annual meeting of the North American Spine Society in Vancouver. He reported a fusion rate of 90.5% and some degree of functional improvement in 93% of patients with pain eliminated or reduced in 85.6% of patients. The data so far for these threaded cages is scanty at best. It is clear that the results are better than those for posterior fusion with or without pedicle screw instrumentation but further studies are needed. Problems with threaded devices will no doubt come to light as they are used under less controlled circumstances in greater numbers of patients.
John Kostuick, M.D., Chief of Spine surgery at John's Hopkins Hospital, Baltimore, Md. (Private Communication with James Nicholson, 2nd R. Roy Camille Meeting, Paris, France, Jan. 28, 1998) vigorously disagrees that fusion can take place within a metal IBF device which shields the bone from load. Dr. Tromanhauser, one of the inventors, in a series of 30 patients implanted with BAK cages, found that at least 9 patients had continued back pain with x-rays and CT scans that were inconclusive for determining fusion. Surgical exploration of these patients has revealed continued motion and no obvious fusion. All patients were explored at least 6 months after cage implantation, a point at which most surgeons would expect fusion.
Recent unpublished research by Dr. Elsig also indicated that 60% of the cases he reviewed had to be reoperated due to failure 6-8 months after initial surgery. There is therefore recognition and belief, especially among Kostuick Fellows who adhere to the principles of Wolfe's law, that loading the bone during fusion through the implant device
Nicholson James E.
Tromanhauser Scott G.
Whipple Dale E.
Cortek Inc.
Smith Jeffrey A.
Williams Frederick C.
Williams & Associates
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