A whole book, about one knee prosthesis! And only half a knee prosthesis at that!
The scope of this book is, actually, a little wider than the exclamations above suggest, but some excuse is surely required. We have written, in fact, about unicompartmental arthroplasty, an intellectually exciting and technically demanding subject for which the authors have a shared enthusiasm. However, since surgical expertise is gained slowly, most practitioners learn only one way of dealing with a particular clinical problem, and we are no exceptions. Our experience of treating unicompartmental arthritis over the last 25 years has been almost exclusively with our own invention, the Oxford Unicompartmental Knee, and we can only write with first-hand authority about that. We have, of course, tried to make good this deficiency from the published reports of other surgeons (whose experience, although different, is usually similarly limited); but, as with other history books, the realistic reader will expect only an attempt at a balanced view, and not necessarily an unbiased attempt.
Until very recently, unicompartmental arthroplasty itself was something of a niche activity. Most orthopaedic surgeons in the world did not use the method at all, and even its champions thought it appropriate for no more than a small proportion of arthritic knees in need of surgery. As will appear, we believe that as many as one-third of those who currently undergo total knee replacement may be better treated by unicompartmental arthroplasty. Soon, a million total knee arthroplasties will be performed in the world each year, and so this book is offered for the consideration of all practising knee surgeons.
The challenge of unicompartmental replacement is nothing less than to replace the deformed surfaces of one compartment of the knee so effectively that the soft tissues of the whole joint, and the retained articular surfaces of the other compartments, can all resume their physiological functions. This is a more difficult task than that confronted by total knee replacement, and it is anomalous that most prosthetic designs and methods of implantation for unicompartmental replacement have remained so unsophisticated during the three decades in which the technology of total replacement has (perhaps unsteadily) advanced.
The undertaking of a unicompartmental arthroplasty requires knowledge of the mechanics of the normal knee, and of the pathological anatomy of the arthritic knee. The prosthesis used must impose no unphysiological limits on the function of the retained structures and therefore it must be implanted in a unique relationship to the ligaments of the individual knee. This may only be consistently achieved if the instruments allow measured intraoperative adjustment of the components to match the particular anatomy. The components need to be sufficiently wear resistant to function for the expected lifetime of the patient, which is usually much longer than 10 years.
Lastly, the surgeon needs to have gained the appropriate skills and experience. Even long familiarity with other procedures on the knee does not, it seems, suffice to avoid the consequences of the ‘learning curve’ for unicompartmental arthroplasty.