Unicompartmental Arthroplasty with the Oxford Knee. Buy the book here.
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Introduction
Osteoarthritis((Floyd 2019 
)) of the knee is one of the most common causes of painful loss of mobility in middle-aged and elderly people in many populations and is the main indication for knee replacement surgery. From the early days of arthroplasty, it was recognised that arthritis was often limited to the medial (or lateral) compartment of the knee and, in the pioneering operation of MacIntosh (1958), metal spacers could be used in one compartment or both. Gradually, however, as the advantages of bicompartmental arthroplasty were appreciated, unicompartmental (or partial) replacement was less and less practised, and in some countries almost disappeared. With the introduction of tricompartmental replacement, a large body of surgical opinion concluded that osteoarthritis of the knee was a disease of the whole joint (like osteoarthritis of the hip) and that common sense required the replacement of all the articular surfaces to provide long-term relief of symptoms.
The attention of designers and manufacturers focused on the improvement of implants and instruments for total replacement, and the gap between the survival rates of unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) widened, reinforcing the prevailing opinion of their fundamental merits.
Popular neglect of the unicompartmental alternative is reflected in a lack of innovation. The St Georg (1969) is still in use today, and most designs developed since are similar to that. Until recently, the components were implanted largely ‘by eye’, as in the early days of total replacement.
A further consequence of the success of TKA was loss of interest in the natural history and pathological anatomy of the osteoarthritic knee. Since total replacement is equally applicable, and almost equally successful, over the whole range of manifestations of that disease, there was no longer much point in its further analysis. However, Ahlback (1968) the longitudinal studies by Ahlback (1968) had already suggested that unicompartmental osteoarthritis does not inevitably spread to other parts of the knee. In addition, numerous post-mortem descriptions published in the 1970s and 1980s had revealed the almost universal presence of cartilage lesions in some parts of the joint in middle-aged and elderly people, implying that their presence is consistent with normal knee function. These observations challenge the common-sense conclusion that replacement of all the articular surfaces is a necessary requirement for a clinically successful arthroplasty.
