Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1998-09-25
2002-03-12
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S075000, C411S538000
Reexamination Certificate
active
06355038
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to multi-axis internal spinal fixation. In more detail, the present invention relates to an internal spinal fixation system, and a method of stabilizing, or fixing, the spine for use with either bilateral rods or plates such as the Steffee/variable screw placement system or a central rod and plurality of cross-bars or plates such as the so-called Tacoma Monorail System, utilizing wedge-shaped and/or flat washers having off-set and/or centered openings therein to provide multiple axes for the pedicle screws used to fix the rods, cross-bars, and/or plates to the vertebrae of the patient.
There are many systems available for internal fixation of the spine. Such systems are described in the patent literature (see, for instance, U.S. Pat. Nos. 4,696,290, 5,092,866, and 5,129,899) and the scientific literature (see, for instance, D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine (Philadelphia: Nanley & Belfus, Inc.) 1992 and H. S. An and J. M. Cotler (Eds.), Spinal Instrumentation (Baltimore: Williams & Wilkins) 1992), and are available from such vendors as AcroMed, Smith & Nephew, MOSS® Miami, Osteonics, Sofamor Danek, and others.
A problem with all such systems, however, is the joint between the screws used to affix the system to the pedicle and the rods, cross-bars, and/or plates of the system. As stated in J. M. Cotler, et al., Principles, Indications, and Complications of Spinal Instrumentation: A Summary Chapter, in H. S. An and J. M. Cotler, Spinal Instrumentation pp. 435-456 (Baltimore: Williams & Wilkins) 1992, “[a] significant problem in pedicular screw fixation appears to be at the site of linkage between the screw and rod or plate.”
It appears that the problems at the site of this linkage may result from the geometry of the joint between the screw and the rod or plate. This difficult geometry results from several factors, including the different angles and placement of the vertebrae and their relative sizes, the shape of the vertebrae and the spacing between vertebrae, the placement of the screws, the lordosis of the spine, and the need to insert the screws into each vertebra at an angle. With regard to the angle of the pedicle screws, pedicle screws are angled inwardly and upwardly into the vertebra for maximum strength and, because the surfaces of the pedicles of each vertebrae are angled relative to each other, the screws rarely line up across the vertebral body into which they are screwed. Nor do they line up from one vertebra to the adjacent vertebra even if the adjacent vertebrae are the same size and shape (which they generally are not). For a more complete discussion of the biomechanics of the bone-implant interface, reference is made to H. A. Pool and R. W. Gaines, Biomechanics of Transpedicular Screw Spinal Implant Systems, in D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine 37-44 (Philadelphia: Nanley & Belfus, Inc.) 1992, M. R. Pinto, Complication of Pedicle Screw Fixation, in D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine 45-54 (Philadelphia: Nanley & Belfus, Inc.) 1992, and M. H. Krag, Vermont Spinal Fixator, in D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine 121-145 (Philadelphia: Nanley & Belfus, Inc.) 1992, which references are incorporated herein in their entirety by these specific references thereto. Because the pedicle screws do not line up, the rod which runs along the longitudinal axis of the patient's spinal column, which provides the structural rigidity required to stabilize the spine, must either be bent to the location of each screw head or the stabilizer must be provided with adjustable structure which enables the screw head to be attached to the rod.
As a result of this difficulty, the literature includes comments such as the following statement in R. M. Puno and J. A. Byrd III, Transpedicular Screw/Rod Fixation Using the Puno-Winter-Byrd(PWB) System, in D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine 83-106 (Philadelphia: Nanley & Belfus, Inc.) 1992:
“Transpedicular fixation has been proved to be of value in the treatment of spinal disorders . . . However, experience has shown that this method of instrumentation places great demand on the surgeon's skill because of the anatomic constraints related mainly to the anatomy and morphometry of the spinal pedicle.”
Many of the above-listed systems, and many of the systems described in the literature, attempt to relieve this burden on the surgeon by providing angled screws (for instance, the AMSET® R-F reduction-fixation system), so-called polyaxial screws (for example, the MOSS® Miami system noted above), full-length, scalloped, open-slot plate design with an undersurface complementary to the shape of the screw head (the Sofamor Danek plate and screw system noted above for example) for optimal positioning of the screws and up to 15° medial-lateral and 30° craniocaudal angulation at the screw-plate interface, and infinitely variable couplers (the so-called Rogozinski spinal rod system for example) which are said to allow rotation through a 130° arc to allow screw placement within the pedicle with no requirement to align each screw with the screw in the adjacent vertebrae.
Although these prior systems address these problems, as evidenced by the fact that new systems are introduced by the same vendors which are already marketing the above-listed systems, no currently available system completely solves all the problems presented by the need for optimal screw placement, angulation of the screw, and effective load transfer from spinal column to implant. An ideal system would (a) accomodate optimal screw placement, height, and angulation, (b) accomodate different sizes and shapes of vertebrae, (c) minimize (or not require) bending or other fabrication during surgery, (d) maintain an angle of approximately 90° between the screw head and the plate or cross-bar to which the screw is attached for effective load transfer from spinal column to implant and to minimize the likelihood of slippage and/or gross failure, and (e) be strong enough to provide lasting and rigid fixation of the spine. Those skilled in the art will recognize that this list is not exhaustive, but is instead intended to illustrate some of the desirable characteristics of an ideal internal fixation system. Other design criteria are also important, and some practicioners may consider some criteria so important that they might not even list others.
So far as is known, none of the above-listed internal fixation systems meets these criteria in every patient. The disadvantages and limitations of currently available systems are made clear from reports in the literature of failure rates (failure of the device, not such complications as infection, phlebitis, seroma, neurologic deficit, etc.) as high as 25% (see R. Roy-Camille, et al., 203 Clin. Orthop. 7 (1986)), 11% (see, S. F. Heim and E. R. Luque, Danek Plate and Screw System, in D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine 201-234 (Philadelphia: Nanley & Belfus, Inc.) 1992), 8% (see, R. M. Puno and J. A. Byrd III, Transpedicular Screw/Rod Fixation Using the Puno/Winter/Byrd (PWB) System, supra), and 2-7% D. M. Arnold and L. L. Wiltse, The Wiltse System of Internal Fixation for the Lumbar Spine, in D. M. Arnold and J. E. Lonstein (Eds.), 6 State of the Art Reviews—Spine: Pedicle Fixation of the Lumbar Spine 55-82 (Philadelphia: Nanley & Belfus, Inc.) 1992.
The currently available systems have other limitations. By way of example, so far as is known, no currently available surgically implanted system can predictably treat rotoscoliosis. Further, no currently available system is conveniently used in multiple level surgery. Multiple level surgery is a
Perumala Corporation
Reip David O.
Wisner Mark R.
Woo Julian W.
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