Unicompartmental knee arthroplasty revisions to total knee arthroplasty

Aims: Data on revision of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) are limited by low patient numbers and short-term follow-up. This study evaluated the mid-term outcomes of revision of UKA to TKA focusing on implant survival, radiological results, and clinical outcomes in a large series. Methods: (SD 6), and 50% were female (n = 118). The most common indications for revision were aseptic loosening (37%; n = 83), progression of arthritis in adjacent compartments (35%; n = 81), and unexplained pain (20%; n = 47). The mean time from UKA to revision to a TKA was four years (26 days to 15 years). Posterior-stabilized constructs were used in 78% of the revisions (n = 184), varus-valgus constrained implants in 14% (n = 33), and cruciate-retaining implants in 7% (n = 16). Metaphyseal fixation devices were used in 8% of cases (n = 18) and augments in 31% (n = 73). Kaplan-Meier implant survival analyses were performed, radiographs reviewed, and clinical outcomes were measured with Knee Society Scores (KSSs). Mean follow-up was eight years (2 to 25). Results: The five-year survival free of any re-revision was 93% (95% CI 89 to 97). There were 17 further re-revisions with femoral and/or tibial aseptic loosening (n = 7), periprosthetic joint infection (n = 4), and stiffness (n = 2) being the most common indications. The five-year survival free of any reoperation was 87% (95% CI 83 to 92). Stiffness (n = 7) and unresurfaced patellar clunk/crepitus (n = 4) were the most common indications for reoperations without implant exchange. There were 25 nonoperative postoperative complications, most commonly stiffness (n = 5), flexion instability (n = 4), and haematoma (n = 4). No unrevised TKAs showed signs of radiological loosening. KSS function score improved from 54 (SD 18) to 69 (SD 26; p = 0.003). Conclusion: In this large series of 235 revisions of UKA to TKA, the five-year survival of the TKAs free of re-revision was good. Our data suggest that the implant survival and clinical outcomes were inferior to primary TKA. Tibial component aseptic loosening was the most common reason for re-revision.