Unicompartmental Arthroplasty with the Oxford Knee. Buy the book here.
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Introduction
Total knee arthroplasty is an effective treatment for most types of arthritis of the knee and requires little of the joint’s anatomy to be intact for a successful outcome. On the other hand, unicompartmental arthroplasty can only succeed if the rest of the knee is functionally intact before surgery. We will discuss, first, the pathology of osteoarthritis (OA) of the knee and then how to ascertain, before operating, that the ligaments are all functionally normal and the retained articular surfaces capable of resuming their weight-bearing role.
History
The components of the OUKA prosthesis were first used (from 1976 to 1984) as a bi-compartmental knee replacement (Fig. 4.1). The patients had severe OA or rheumatoid arthritis and since, at that time, there were no proven alternative treatments, there were no specific indications. The first step towards defining a role for the implant was taken when the results of these operations were reviewed and it was found that the anatomical state of the anterior cruciate ligament (ACL) at the time of surgery was an important determinant of the long-term outcome (Goodfellow & O’Connor, 1986). In 1992, we reported a six-fold difference in the 7-year cumulative survival of the prosthesis between knees with or without a functioning ACL at the time of surgery, irrespective of the primary disease and of all the other variables measured (Goodfellow & O’Connor, 1992). This was the first publication to offer statistical evidence of the importance of that ligament in the kinematics of unconstrained resurfacing implants. During the same period we had, incidentally, observed that in osteoarthritic knees with an intact ACL, articular surface damage was usually limited to the medial compartment, with the rest of the joint remaining healthy. Taken together, the two observations suggested that these cases would be appropriate for treatment with the meniscal prosthesis and, since 1982, the implant has been mainly used for medial replacement in OA knees with an intact ACL (Goodfellow et al,. 1987).
Subsequently, we published a more detailed study of the pattern of cartilage damage in arthritis, correlating the preoperative clinical and radiological signs with the intraoperative findings during unicompartmental surgery (White et al., 1991). In that paper we introduced the term ‘anteromedial osteoarthritis’ to describe the subgroup of varus knees in which both cruciate ligaments and the MCL are functionally normal, and in which the cartilage and bone erosions on the tibial plateau are in the anterior and central parts of the medial compartment with a corresponding lesion on the inferior medial femoral condyle.
We now believe that anteromedial OA is the most common indication for UKA and is present in about half the patients needing knee replacement. The condition can be recognised by a consistent association between the clinical and radiological signs and the pathological lesions that cause them.
