Results and Registry Data for Unicompartmental Knee Replacements

There is good evidence that Unicompartmental Knee Replacement (UKR) has numerous advantages over Total Knee Replacement (TKR). UKR provides a faster recovery with a shorter hospital stay, fewer complications, lower re-admission rate and lower mortality. In addition, it provides better functional outcomes with more excellent results. UKR is also easier to revise than TKR, is less costly, and more effective over the patient’s lifetime. The disadvantage of UKR is that it has a higher revision rate. One of the main reasons for this is that the threshold for revising a UKR is much lower than that for TKR because UKR are easier to revise, and the outcome of a revision is expected to be better. As a result, even though UKR have less poor outcomes than TKR, they have a higher revision rate. So, when deciding whether to do a UKR or TKR, surgeons should not just focus on the revision rate but instead should consider all factors important to patients. Registry data shows that most surgeons doing UKR do very small numbers, the most common being 1 or 2 per year. Surgeons doing small numbers have very high revision rates, and with increasing numbers the revision rate decreases. The only practical way surgeons can increase their UKR caseload is to increase the proportion of their primary knee replacements that are UKR, which is known as UKR usage. Surgeons with usage less than 20% tend to have a high revision rate so these surgeons should either stop doing UKR or do more. With mobile bearing UKR the revision rate decreases with increased usage up to 50%. The evidence-based indications for the mobile bearing UKR are satisfied in about 50% of patients needing knee replacement. Therefore, to achieve optimal results surgeons should adhere to the recommended indications. There are a few studies that report the 20-year results following UKR. The largest which included 683 knees, reported a 20-year survival of 91% (n=683) for a mobile bearing UKR. Three smaller studies of fixed bearing UKR reported 20-year survivals of 74% (n=160), 84% (n=103) and 90% (n=90). There are numerous reports of 10-year results from cohort and registry studies with a number of devices performing well. There are very few comparative studies at 10-years, but a matched registry-based study found that for mobile bearing UKR cementless fixation had a better ten year survival than cemented.