Surgical Techniques - Unicompartmental Knee Replacement
When only the inner (medial) side of the knee has worn down with advanced arthritis, and the remainder of the knee has little wear with intact structural ligaments, this may be an opportunity to replace only this damaged medial compartment of the knee. This procedure is called partial or unicompartmental knee replacement and is now a popular and scientifically supported method of resolving the arthritic pain of only the inner aspect of the knee. The majority of patients with knee arthritis do not qualify for this more conservative surgery as they have worn away too much of their knee joint for this lesser surgery to be successful. In fact only about 10% of patients seen are typically candidates for this procedure.
Those select patients who do qualify for this unique solution to their knee pain get a short 3" incision over the medial aspect of their knee, are taught to walk with a walker or crutches in the recovery room and then go home the same day. Most physically fit patients are walking with only a cane in just a few days to a week after uni knee surgery and are usually able to return to full activity within a few weeks after surgery.
There are several great advantages of a unicompartmental knee replacement when compared to a total knee replacement. First, the typical uni knee patient will have increased motion in their knee after completing therapy above what typical total knee replacement patients will realize. Second, the motion through flexion and extension will seem more natural because the anterior cruciate ligament is maintained in uni knee surgery, but removed in a total knee resulting in a different, more mechanical feeling. Third, this more bone conserving operation allows for the progression to a standard total knee replacement in those very few patients who either wear out the remainder of the maintained knee or have a loosening failure of the implant. Finally, most unicompartmental knee patients recover to active function quicker than a typical total knee replacement patient.
Partial Knee Replacement with the Oxford Uni Knee
The implants for this technique have greatly improved over the past 3 decades and there are many varieties of implants from which to choose for a partial knee replacement. Dr. Zehr has decided that the Oxford Unicompartmental Knee is the best for his patients. It is the only mobile bearing unicompartmental knee available in this country and as such offers greater flexibility than many of the other prosthetic options.
There are many surgeons who do not offer a unicompartmental knee replacement to patients based on their incorrect bias that unicompartmental knee replacements will not hold up over time. In fact, the scientific studies of the Oxford knee replacement show just the opposite is true. In long term studies of the Oxford Knee in the correctly chosen patient, the longevity of this implant follows a similar survival curve of total knee implants with various authors reporting 98% survival at 10 years1, 94% survival at 15 years2 and incredibly 91% survival at 20 years out from surgery3.
The Oxford Knee has been available worldwide since 1980, but available in this country only since 2005. In order to become a qualified surgeon to implant the Oxford Knee a surgeon must be trained by the original Oxford Knee surgeons. As such, Dr. Zehr spent time in Oxford, England prior to its release here in the U.S. learning the specifics and nuances of this unique prosthesis and has been using this globally preferred implant since its arrival here.
Included below is a basic animation of the steps involved in uni knee replacement and an example of post-operative X-rays of the implants to provide some basic understanding of this complex procedure.
1. Murray DW, et al: The Oxford medial uniccompartmental arthroplasty: a ten-year survival study. JBJS (Br), 1998, 80-B:983
2. Svard UC, et al: Oxford medial unicompartmental knee arthroplasty: a survival analysis of an independent series. JBJS (Br),2001; 83:191.
3. Price AJ et al: A second decade lifetable survival analysis of the Oxford unicompartmental knee arthroplasty . Clin Orthop , 2011; 469:174