Knee prostheses

Abstract

A total knee prosthesis comprises a femoral component and a patellar component. The femoral component has a patellar flange into which is built a twist or roller coaster configuration. The patellar component has an off-set dome with respective lateral and medial facets. The configuration of the patellar flange resists forces from a medial to a lateral direction, whilst the lateral and medial facets of the patellar component are respectively shaped to allow area contact and line contact respectively with the femoral component. Also disclosed is a device for intra-operative checking of patellar tracking to allow correct insertion of the femoral and patellar components.

Description

FIELD OF THE INVENTION[0001]This invention relates to improvements in or relating to knee prostheses, and is particularly concerned with the patellofemoral interface.BACKGROUND OF THE INVENTION[0002]The patellofemoral joint is a troublesome area in conventional total knee replacement design. A significant number of patients are left with discomfort from the patellofemoral region following total knee replacement and others have failure such as lateral patellar mal-tracking, wear through of polyethylene patellar components, fracture of patellar components, loosening of components and fracture of the patella bone itself, requiring revision surgery.[0003]In order to obviate the point loading and high wear using a conventional domed polyethylene patellar button, U.S. Pat. No. 4,309,778 discloses a highly conforming patellar button giving area contact. However because this type of articular surface is highly conforming to the femoral component design that it is matched to, a fixed bearing...

AI Technical Summary

Benefits of technology

"The tracking instrument allows the Surgeon to detect any discrepancy between where the patella wants to be and where the patellar button wants to be. The Surgeon can address this by several maneuvers, such as adjusting the trial femoral component and the tracker base plate on the patella, choosing a patellar button with a greater off-set, or performing a lateral retinacular release. These measures can improve the accuracy of the patent and reduce the risk of complications."

Problems solved by technology

The patellofemoral joint is a troublesome area in conventional total knee replacement design.

A significant number of patients are left with discomfort from the patellofemoral region following total knee replacement and others have failure such as lateral patellar mal-tracking, wear through of polyethylene patellar components, fracture of patellar components, loosening of components and fracture of the patella bone itself, requiring revision surgery.

However because this type of articular surface is highly conforming to the femoral component design that it is matched to, a fixed bearing of this design would not allow the normal patellar rotation which occurs in use.

This prior art design was however found to be susceptible to failure, and in The Journal of Arthroplasty, Volume 20, No. 2, 2005, pages 202-208, an article by Huang at al. describes failures of this type of design, pointing out that this type of patellar replacement is highly sensitive to patellar mal-tracking.

As there is a finite allowable thickness of patella replacement, when a (metallic) base plate is added to a patellar button design, of necessity the polyethylene articular portion has a very thin layer, making the design highly susceptible to point loading.

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