**6.3 Total joint replacements and arthrodesis**

Total joint replacement (TJR) has to be considered in patients with radiographic evidence of hip/ knee OA who have refractory pain and disability. Principally, OA occurs less commonly at ankle, elbow, and wrist and thus total joint replacements are less frequent at these sites than at the hip or knee. In the last few years, interest in total knee arthroplasty has resulted in a proliferation of prosthetic designs, and many different types are now aaialble.

The indications for TJR have evolved and are expanding. Currently TJR are offered to patients earlier in the course of the disease as the risks of complications associated with TJR have reduced dramatically.

The prostheses available are:


The selection of a suitable prosthesis is dependent on the type and the indications

Types of prostheses

1. Unicondylar

This is an anatomically designed replacement for either the medial or the lateral femoral tibial articulation. It is designed to allow 120 degrees of flexion. The *unicondvlar* prosthesis is used only for cornpartmental OA.

2. Duocondylar

The femoral component of the duocondylar prosthesis is similar in shape to that of the unicondylar model except that there is no anterior flange and instead the halves are connected by an anterior cross bar which is countersunk during insertion. Because of its anatomical shape, it is most suitable when deformity, instability, and flexion contracture are not too severe.

3. Geometric

The prosthesis is non-anatomical in that the curvature of the femoral component is of constant radius. The plastic tibial component is in one piece, with two halves connected by an anterior bar. The prosthesis is designed to allow a 90- degree arc of motion. The cruciate ligaments are preserved. Two sizes are available.

4. Guepar

The Guepar is a Vitallium hinge prosthesis (improved over the Young model) which is fully constrained, providing motion in a fixed axis without rotation. Guepar prosthesis was used in knees with extrerne deformity or instability due to rheumatoid arthritis and OA.

Innovation continues to characterize the TJR field. This clinical dilemma has stimulated a search for biomaterials that produce less wear debris and, in turn, cause less osteolysis, attendant bone loss, and implant failure. This is the rationale for several developments, including highly cross-linked polyethylene and ceramic- on-ceramic and metal-on-metal bearing surfaces.
