Abstract
The evidence to help the surgeon decide on the merits of which type of replacement to offer their patients is steadily mounting and comes from large datasets such as joint registries.
There are many advantages of UKR vs TKR such as satisfaction, function, recovery, morbidity, mortality and cost but there is one major disadvantage. All registries show a higher failure rate with UKRs.
Registries show that there are more excellent and fewer poor Patient Reported Outcome Measure Scores (PROMS) with UKR compared to TKR and the higher revision rate is in major part due to the threshold of revision. For instance, 60% of UKR are revised vs 10% of TKR with an Oxford score that is worse post-operation than pre-operation. Ease of revision with UKR is a major determinant of the higher revision rate.
The real issue with UKR relates to usage. Most surgeons perform very few UKR on young patients with early arthritis viewing the procedure as a pre-TKR. Low surgeon volume equates to high revision rate in the national registries. Surgeons should either abandon UKR or do an adequate number to ensure success.
Surgeons can improve their results by increasing their usage of UKR. The Unicompartmental Knee National Joint Registry (UKNJR) data shows that the optimal usage of the mobile UKR is between 20 and 50% of replacements. Fixed bearing usage is optimal at 20% but not higher.
The other major advantage concerns the lower mortality rate with UKR. At 90 days it is less than half that of TKR and even at 8 years it is 10% less. For every 10 UKRs performed rather than TKR then one life is saved at 8 years.
There is very little evidence suggesting that bi-UKR is necessary certainly with the mobile UKR. There is evidence, however that patellofemoral joint problems are a problem with fixed bearing UKR in the second decade.
