Does Unicondylar Knee Arthroplasty Failure Mode Impact Conversion Total Knee Arthroplasty Outcomes?

Unicondylar knee arthroplasty (UKA) conversion to total knee arthroplasty (TKA) is associated with greater resource utilization and morbidity than primary TKA. However, it is unclear how the indication for conversion to TKA impacts outcomes. This study evaluated if aseptic UKA failure mode affects subsequent TKA survivorship at a high-volume institution.

A prospectively maintained institutional database was queried for all conversion TKA, primary TKA, and first-time revision TKA performed by nine surgeons between 2000 and 2023. This resulted in 439 UKA conversions to TKA and comparator groups of 15,026 primary and 1,432 revision TKAs. Conversions were grouped by UKA failure mode, with a focus on the 413 aseptic failures. The primary outcome measure was aseptic conversion TKA survivorship using revision for any reason as an end point. Secondary outcomes included survivorship between all TKA procedures. The mean follow-up length for conversion TKAs was 5.7 (range, zero to 22.4) years.

There were no statistically significant differences in survivorship between conversion TKAs based on their aseptic UKA failure mode (P = 0.80). The most common reasons for conversion of UKA to TKA were progression of osteoarthritis (129 of 413), tibial component loosening and subsidence (112 of 413), polyethylene wear with osteolysis (93 of 413), femoral component loosening (38 of 413), and tibial fracture (17 of 413). There were 11 conversion TKAs that required subsequent revision. The overall survivorship of aseptic conversion TKA was similar to primary TKA (P = 0.72), with 10-year rates of 95.6% (95% CI [confidence interval], 91.7 to 97.7) and 95.8% (95% CI, 95.3 to 96.3), respectively. Both procedures demonstrated greater survivorship than aseptic revision TKAs (P < 0.001), which had a 10-year rate of 84.2% (95% CI, 80.5 to 87.3).

Our institutional experience demonstrated that UKA conversion to TKA can be successfully performed regardless of aseptic UKA failure mode. Survivorship of aseptic conversion TKA was similar to that of primary TKA for up to 10 years and significantly better than that of the first-time revision TKA.