Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-10-18
2004-02-10
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S099000
Reexamination Certificate
active
06689132
ABSTRACT:
BACKGROUND OF THE INVENTION
The human spine is made up of a column of thirty-three bones and their adjoining structures. The bodies of these vertebrae are connected by anterior and posterior ligaments and by discs of fibrocartilage generally known as intervertebral discs. These discs are positioned between opposite faces of adjacent vertebral bodies. This column of vertebrae and intervertebral discs form a central axis that supports the head and torso. These vertebrae also enclose an opening through which the spinal cord passes.
The presaccral vertebrae are normally held in position to one another by the intervertebral discs, ligaments and musculature of the body. These vertebrae move relative to adjacent vertebrae thus permitting the head to be turned relative the body and providing a wide range of flexibility to the spine.
One of the most costly health problems in society involves back pain and pathology of the spine. These problems can affect individuals of all ages and can result in great suffering to victims. Back pain can be caused by several factors such as congenital deformities, traumatic injuries, degenerative changes to the spine, and the like. Such changes can cause painful excessive motion, or collapse of a motion segment resulting in the contraction of the spinal canal and compression of the neural structures, causing debilitating pain, paralysis or both, which in turn can result in nerve root compression or spinal stenosis.
Nerve conduction disorders can also be associated with intervertebral discs or the vertebrae themselves. One such condition is herniation of the intervertebral disc, in which a small amount of tissue protrudes from the sides of the disc into the foramen to compress the spinal cord. A second common condition involves the development of small bone spurs, termed osteophytes, along the posterior surface of the vertebral body, again impinging on the spinal cord.
Upon identification of these abnormalities, surgery may be required to correct the problem. For those problems associated with the formation of osteophytes or herniations of the intervertebral disc, one such surgical procedure is intervertebral discectomy. In this procedure, the involved vertebrae are exposed and the intervertebral disc is removed, thus removing the offending tissue or providing access for the removal of the bone osteophytes. A second procedure, termed a spinal fusion, may then be required to fix the vertebrae together to prevent movement and maintain a space originally occupied by the intervertebral disc. Although this procedure may result in some minor loss and flexibility in the spine, due to the relatively large number of vertebrae, the minor loss of mobility is typically acceptable.
During an intervertebral discectomy, a prosthetic implant or spinal implant is inserted in the vertebral disc space. This prosthetic implant is often a bone graft removed from another portion of the patient's body, termed an autograft. The use of bone taken from a patient's body has the important advantage of avoiding rejection of the implant, but has several shortcomings. There is also a risk of opening a second surgical site to obtain the implant, which can lead to infection or pain for the patient, and the second surgical site is weakened by the removal of material. The bone implant may also not be perfectly shaped for placement between the vertebrae, thus leading to slippage or absorption of the implant, or failure of the implant to fuse with the vertebrae.
Other options for a graft source of implant are bone removal removed from cadavers, termed allograft, or from other species, termed a xenograft. In these cases, while there is the benefit of not having a second surgical site, thus reducing the incidence of infection or pain at such second site, there is increased difficulty associated with graft rejection and the risk of transmitting communicable diseases.
An alternative approach to using a bone graft is using a manufactured implant made of synthetic material which is biologically compatible with the body and the vertebrae. Several compositions and geometries of such implants have been utilized, ranging from simple blocks of material to carefully shaped implants, with varying success.
There has been an extensive number of attempts to develop an acceptable prosthetic implant that can be used to replace an intervertebral disc and yet maintain the stability of the intervertebral disc space between adjacent vertebrae, at least until complete arthrodesis is achieved. For fusion to occur between the prosthetic implants, it is typically necessary to prepare the vertebrae to be fused by breaking through or cutting into the hardened outside plates of the bone to allow the interposed bone graft to come into direct contact with the prosthetic implant, thereby tricking the body into attempting to heal itself and to bond with the prosthetic implant. While many types of synthetic prosthetic devices have been proposed, the success rates have been low and the surgical procedures have been complicated and often traumatic to the patient.
One of the more prevailing designs of these prosthetic implants takes the form of a cylindrical implant. These types of prosthetic implants are represented by Brantigan U.S. Pat. No. 4,878,915 and Ray U.S. Pat. No. 4,961,740, which are incorporated herein by reference. In these cylindrical implants, the exterior portion of the cylinder can be threaded to facilitate insertion of the prosthetic device. Some of these prosthetic implants are designed to be pounded into the intervertebral disc space. These types of devices are represented in Brantigan U.S. Pat. No. 4,834,757 and Brantigan U.S. Pat. No. 5,192,327, which are incorporated herein by reference. The Brantigan and Ray patents disclose prosthetic implants wherein the transverse cross-section of the implant is constant throughout the length of the implant, and is typically in the formed of a circular cylinder.
Other prosthetic implants have been developed that do not have a constant cross-section. For instance, the patent to McKinna U.S. Pat. No. 4,714,469 illustrates a spherical implant with elongated protuberances that project into the vertebral end plate. The implant of Bagby U.S. Pat. No. 4,934,848 is in the form of a sphere which is positioned between the centrums of the adjacent vertebrae. Both of these disclosures are incorporated herein by reference.
Various prosthetic implants can be generally divided into two basic categories, namely solid implants and implants designed to encourage bone growth. Solid implants are represented by U.S. Pat. Nos. 4,878,915 and 4,349,921, which are incorporated herein by reference. The other patents discussed above permit bone to grow across and/or into the implant. It has been found that devices which promote natural bone growth achieve a more rapid and stable arthrodesis. These implants are typically filled with autologous bone prior to insertion into the intervertebral disc space. These implants typically include apertures which communicate with openings in the implant, thereby providing a path for tissue growth between the vertebral end plate and the bone or bone substitute within the implant.
A number of difficulties remain with the use of these prior art prosthetic implants. While it is recognized that hollow implants which promote bone growth into the implant is an optimal technique for achieving fusion, most of these devices have difficulty achieving this fusion, at least without the aid of some additional stabilizing device, such as a rod or plate. Moreover, some of these devices are not structurally strong enough to support the heavy loads applied to the most frequently fused vertebral levels, namely those in the lower lumbar spine.
Many of these problems with past prosthetic implants have been overcome by the prosthetic implants disclosed in U.S. patent application Ser. No. 09/865,114 filed May 24, 2001 entitled “Spherical Spinal Implant” and U.S. patent application Ser. No. 09/494,645 filed Jan. 31, 2000 entitled “Spinal Fusion Implant”, now U.S. Pat.
Fay Sharpe Fagan Minnich & McKee
Reip David O.
Spineco, Inc.
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