Abstract
Introduction
It has been hypothesized that a unicompartmental knee arthroplasty (UKA) is more likely to be revised than a total knee (TKA) because conversion surgery to a primary TKA is available. The purpose of this study was to determine if there is a lower threshold for UKA revisions compared to TKA revisions based on Oxford Knee Scores and range of motion (ROM).
Methods
We retrospectively reviewed 636 aseptic revision cases performed between 1998 and 2018. This included 137 UKAs that underwent conversion to TKA and 499 TKA revisions. Pre-revision age, body mass index (BMI), time in situ, Oxford Knee Scores, and ROM were available for all patients. T-tests were performed to determine if significant differences existed between the two groups. The minimal clinically important difference (MCID) when comparing Oxford scores between cohorts has been reported as 5 points.
Results
There were no differences between the two groups based on gender, BMI, age, or time to revision. The top three reasons for revision are different. TKR revision diagnoses were loosening 43%, instability 18% and wear 13%. UKA revision diagnoses are progression of OA 37%, loosening 36%, and wear 12%. All UKA were converted to TKA while there were 440 partial and 59 all component TKR revisions. Out of a maximum 48 points, the mean Oxford score of the UKAs before revision was 23±9.5, which was significantly higher than the TKAs at 19.3±9.7 (p<0.001). UKA patients scored statistically better on nine of the twelve Oxford questions with no difference in pain, walking, and sit to stand questions. Revised UKA had greater pre-revision ROM (1140) than TKR (990, p<0.001).
Conclusion
The mean UKA Oxford scores prior to revision were significantly better than pre-revision TKA scores and better on 9 of 12 individual Oxford questions. However, the 3.7 point mean difference is less than the 5 point MCID for the Oxford Knee Score. This study suggests that at our institution there may not be a difference in patient reported Oxford preoperative scores between UKA and TKR revisions implying that we are not more likely to revise a UKA than a TKA. This is not surprising since our center does a high volume of UKA. We have also performed sub analyses comparing UKA revision scores to partial and both component TKA revision scores.
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