Candidates for unicondylar replacement

• One knee compartment involved
  • Medial or lateral
• Willing to accept the need for revision to a total knee if - it does not work
• Age
  • Young (less than 60 year old) – a reasonable option to - consider
  • Older (75+) – probably not
  • Role in 60-75 year old – the indications are not clear at present

Who is a “good” candidate for a partial replacement? Most importantly, it has to be a patient with a knee where arthritis affected only one compartment – medial or lateral. The ligaments in the knee must be intact, the patient has to be willing to accept the risk of possible operational failure, and the potential need for conversion to a total knee, as it could fail due to inadequate pain relief, progression of arthritis in the rest of the knee, or because of failure of the components.

Because of the uncertainties mentioned above, I generally would consider the partial replacement over total replacement patients who are under 60 years of age. For a patient under 60 years old, a partial replacement may “buy some time”. If the partial replacement later fails when the patient is 65-70 years old, the conversion to a total knee could provide the patient with a “good” knee for the rest of his/her expected life. Inserting a total knee replacement in a young patient could likely mean difficult revision surgery 15 or 20 years later. Of course the younger patient has to fulfill all of the other mentioned requirements to qualify for such an operation. According to statistics only about 5-10% of patients with osteoarthritis (all age groups) are candidates for a partial knee replacement.

There is controversy when it comes to recommending partial knee replacement in an older person, with a statistical life expectancy of less than 10 - 15 years. Partial replacement is a much less stressful operation, with less probability of complications, and so may a better option for those patients. On the other hand if it fails in the first few years, as it does in up to 20% of cases, subjecting an elderly patient to yet another, bigger operation may be a deterrent. Personally, given the current safety and outcome data for total knee replacement surgeries my preference is to do a total knee replacement in the elderly.

Partial knee replacement can also be very successful in the 65-75 year old patient. However, given the early failure rate of up to 20% in the first couple of years after the surgery, it makes sense to implant a much more reliable and predictable total knee replacement in those patients, in my opinion. With current survivorship of total knee replacements of 80-90% at 15-20 years, it seems to be a better option in this age group.