Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-12-19
2003-05-27
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020280, C623S020330, C623S020340
Reexamination Certificate
active
06569202
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
Prosthesis components for replacing large anatomical joints are well known in the art, including knee, shoulder, and ankle replacement systems. For example, knee replacement systems typically include femoral components that replace all or part of the joint surfaces of the end of the femur and tibial components that replace all or part of the upper surface of the tibia. The tibial component typically has two parts, a metal tray or shell that is affixed directly to the upper end of the tibia with bone screws, with cement, or with bone ingrowth into a porous undersurface of the tray, and a polymeric (e.g., polyethylene) liner secured within the tray. The lower end of the femoral component typically rounded lower end that simulates the condylar process of the femur. This condylar surface of the femoral component bears on the upper surface of the liner and permits articulation of the knee. The articulation of the femoral component on the polyethylene liner results in microscopic particles of polyethylene being worn from the liner. The metal trays typically have screw holes which receive bone screws that are anchored into the tibia to enhance immediate fixation. However, these screw holes can cause problems by allowing joint fluid along with the polyethylene debris to be forced into the screw holes under pressure and thus dissolve and destroy the bone structure supporting the tray. Even when occupied by a screw, the screw holes allow joint fluid and debris to migrate around the screw and to come into contact with the underlying bone structure, gradually loosening it and destroying bone.
Some efforts have been made to address these problems in the prior art. The polyethylene liner or component has been locked securely to the metal tray with a peripheral locking flange to prevent up and down motion of the polyethylene component and resultant high pressure pumping of joint fluid into the screw holes. These tight capture mechanisms do not, however, prevent joint fluid from bathing the screws, and in situations in which joint fluid pressure is elevated, such higher levels of joint fluid pressure can be transmitted to the screw holes, thus forcing joint fluid through the screw holes and into the bone proximate the screw holes and resulting in bone loss around screws and under empty screw holes. Over time, this loss of bone supporting the tray jeopardizes the structural integrity of the knee replacement system.
Another approach to minimizing the danger of bone loss is to minimize the wear on the under surface of the polyethylene component by polishing the metal tray. However, it has been found that most of the wear debris is generated at the actual bearing surface between the femoral and tibial joint surfaces, and is not affected by polishing the under surface of the polyethylene component.
Still another approach is to develop tibial trays with no screw holes. While this would eliminate the route of access of joint fluid and debris into the underlying bone, it eliminates the use of screws, which are a desirable or even necessary feature for fixation of the metal tibial tray onto the bone surface, particularly in patients with soft bone.
Reference may be made to my prior U.S. Pat. No. 5,766,260 entitled “Acetabular Component With Improved Liner Seal and Lock”, issued Jun. 16, 1998, which disclosed modular acetabular components in a total hip replacement system. In particular, my prior '260 patent disclosed a continuous flexible seal on a part spherical plastic liner which sealingly engaged its part spherical metal shell for continuous 360° sealing around the liner. More specifically, as the liner was installed in its acetabular shell, the liner would flex and would thus make a continuous seal with respect to the shell and a snap-lock securement was provided to secure the part-spherical liner within the part-spherical shell. This acetabular liner was fixedly secured to its shell by means of peripheral tabs on the liner which were received in corresponding notches in the shell, and by means of interlocking ridges extending around the part spherical shell which were received in a continuous interlocking groove on the inner face of the shell.
As reported in a paper entitled “Effect of Locking Mechanism On Particle and Fluid Migration Through Modular Acetabular Components”, by Cyna Kalily et al., presented at the 64
th
Annual Meeting of the American Academy of Orthopaedic Surgeons, Feb. 13-17, 1997, a seal, such as described in the above-noted '260 patent, which was incorporated in the MicroSeal® hip system (similar to that described in my '260 patent) commercially available from Whiteside Biomechanics, Inc., of St. Louis, Mo., was effective in preventing the migration of joint fluid and debris between the liner and the metal shell. Because the continuous seal of the MicroSeal® hip system prevented joint fluid from passing coming into contact with the bone structure under the tray, degeneration of bone structure proximate the bone screws anchoring the shell would be considerably lessened.
As noted above, it has been known that the migration of joint fluid and debris through the screw holes in a tibial tray in a total knee replacement system caused degeneration of the tibia supporting the tibial tray. However, in attempting to incorporate a continuous seal, such as disclosed in the '260 patent, which was only used with a part spherical shell in a tibial tray in a knee replacement system, it was found that continuous peripheral tabs and corresponding continuous notches and the locking ridge/locking groove arrangement disclosed in the '260 patent would not permit a surgeon to snap lock the liner into the tibial tray. This is due to the fact that in knee, ankle, shoulder and other large joint replacement systems, the liner component cannot be laid directly symmetrically on the metal shell (e.g., on the tray) component and pressed into place, as it can be in inserting a liner in an acetabular shell of a hip replacement system. Typically, the liners for such other joint replacement systems must be inserted from the front, side or back because of the presence of tissue, ligaments or the like. Because of the necessity of the front, side or back insertion of the liner into its tray, the surgeon oftentimes cannot apply a load directly to the center of the polymeric liner of sufficient magnitude to drive the liner into place within its tray or shell component. It has also been found that due to the difficultly of inserting such liners into their respective tray or shell components, the close tolerances required to prevent movement of the liner with respect to the tray during usage of the appliance by the patient could not be maintained.
In summary, there has been a long-standing need for a joint replacement component (e.g., a tibial tray) and liner which are of non-spherical or non-circular shape that effectively prevents the migration of joint fluid and debris from the tray to the bone structure receiving the bone screws which secure the tray to the tibia, which maintains the close tolerances needed to rigidly secure the liner within the tray to prevent relative movement, and yet which liner can be readily installed by the surgeon once the component (tray) has been affixed to the tibia.
SUMMARY OF THE INVENTION
Among the several objects and features of the present invention may be noted the provision of a joint replacement component, such as a non-part spherical tibial tray for a knee replacement system, and a non-part-spherical polymeric (polyethylene) liner having a continuous seal integrally formed on the liner and extending completely around the liner for continuously sealing the liner with respect to the tray thereby to prevent the migration of joint fluid and other debris (or contaminants) from the tray to the bone structure supporting the tray via bone screw holes in the tray which is easy for the surgeon to install and which is securely held in place where the line
Miller Cheryl
Polster Lieder Woodruff & Lucchesi L.C.
Snow Bruce
Whiteside Biomechanics, Inc.
LandOfFree
Tray and liner for joint replacement system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tray and liner for joint replacement system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tray and liner for joint replacement system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3076602