Revision of unicompartmental arthroplasty to total knee arthroplasty: not always a slam dunk!

Objective: As the number of UKA performed in the world continues to increase, so will the number of failures. A better understanding of the outcomes after revision UKAto TKA is warranted. The objective of this study is to report the outcomes of modern UKA revised to TKA in three US centers.

Methods: A total of 175 revisions of medial UKA in 168 patients (81 males, 87 females; average age of 66 years) performed from 1995 to 2009 in three institutions and with a minimum of 2-year clinical follow-up were reviewed. Individual joint registries and chart reviews were performed to collect data regarding reasons for revision, type of implants used, and re-revision rates.

Results: The average time from UKA to revision TKA was 71.5 months (range 2 months to 262 months). The four most common reasons for failure of the UKA were femoral or tibial loosening (55%), progressive arthritis of the lateral or patellofemoral joints (34%), polyethylene failure (4%) and infection (3%). The average follow-up after revision was 75 months. Nine of 175 knees (4.5%) were subsequently revised at an average of 48 months (range 6 months to 123 months.) The rate of revision was 1.23 revisions per 100 observed component years. The average Knee Society pain and function score increased to 75 and 66, respectively.

Conclusions: In the present series, the re-revision rate after revision TKA from UKA was 4.5 % at an average of 75 months or 1.2 revisions per 100 observed component years. Compared to published individual institution and national registry data, re-revision of a failed UKA is equivalent to revision rates of primary TKA and substantially better than re-revision rates of revision TKA. These data should be used to counsel patients undergoing revision UKA to TKA.