Lower re-revision rates after UKA-to-TKA than UKA-to-UKA revision for failed medial unicompartmental knee arthroplasty at mid-term follow-up.

PURPOSE: Revision following unicompartmental knee arthroplasty (UKA) remains challenging, and optimal revision strategy is still debated. This study analysed failure mechanisms after aseptic medial UKA revision and compared mid-term outcomes between UKA-to-UKA and UKA-to-total knee arthroplasty (TKA) revision procedures.

METHODS

A retrospective single-centre study included 113 consecutive aseptic UKA revisions performed between 2001 and 2020. Patients were stratified into UKA-to-UKA (n = 38) and UKA-to-TKA (n = 75) groups. Progression of lateral osteoarthritis (31%) and aseptic loosening (27%) were the most common indications for revision. Re-revision rates were evaluated and implant survival was assessed using Kaplan-Meier analysis with log-rank testing and Cox regression. Functional outcomes were evaluated using validated patient-reported outcome measures (Oxford Knee Score, Knee Society Scores, UCLA activity score, visual analogue scale) and range of motion.

RESULTS

During follow-up, re-revision occurred in 8 of 38 UKA-to-UKA revisions (21.1%) and in 3 of 75 UKA-to-TKA revisions (4.0%). Re-revision after UKA-to-TKA revision occurred due to suspected early infection (n = 2) and aseptic loosening (n = 1), whereas after UKA-to-UKA revision the main causes were aseptic loosening (n = 3), unexplained pain (n = 3) and bearing dislocation (n = 2). Overall, 10-year implant survival was 89.7%. Implant survival at 10 years was higher following UKA-to-TKA revision compared with UKA-to-UKA revision (95.3% vs. 78.6%; log-rank p = 0.003). PROMs did not differ significantly between groups, whereas range of motion was greater after UKA-to-UKA revision (126° vs. 114°, p < 0.001).

CONCLUSION

Conversion of medial UKA to TKA was associated with lower re-revision rates compared with UKA-to-UKA revision, while patient-reported outcomes were comparable between strategies. UKA-to-UKA revision may remain appropriate in selected cases with surgically addressable failure mechanisms. These findings support an individualised revision strategy based on the underlying cause of failure.

LEVEL OF EVIDENCE: Level III, retrospective cohort study.