Excellent functional outcome and satisfactory revision rates of two-staged bicompartmental knee arthroplasty for disease progression following unicompartmental knee arthroplasty.

Purpose: Disease progression in the untreated compartment is the leading cause for reoperation following unicompartmental knee arthroplasty (UKA). A less-invasive alternative to total knee arthroplasty (TKA) conversion is the addition of a second UKA. The study assessed survival, functional, and radiological outcomes after two-staged bicompartmental UKA.

Methods: A retrospective analysis was performed on 102 knees (98 patients, mean age 73.7 years) who received an additional medial (n = 29) or lateral UKA (n = 73) between 2016 and 2025 with a minimum follow-up of 1 year. Primary outcomes were cumulative revision rates for (1) any reoperation and (2) implant revision. Functional outcomes included the Oxford Knee Score (OKS) and UCLA (University of California, Los Angeles) Activity Score. Radiographic assessment included measurement of the hip-knee-ankle angle (HKAA).

Results: The mean follow-up was 4.0 years (SD 2.1). At 9 years, cumulative survival rate was 84.3% (95% CI: 0.763-0.923) for any reoperation and 89.3% (95% CI: 0.822-0.964) for implant revision. There were nine implant revisions (8.8%), most commonly due to medial mobile-bearing dislocation (44.4%). In 50%, implant revision to TKA was performed using primary non-modular components. Mean postoperative OKS and UCLA scores were 40.4 (SD 8.0) and 5.5 (SD 1.7), respectively. Medial osteonecrosis (ON) following primary lateral UKA accounted for 38% (11/29) of all indications for an additional medial UKA, and was associated with greater HKAA correction following prior lateral UKA.

Conclusion: Two-staged bicompartmental UKA is a viable less-invasive alternative to TKA conversion for patients with disease progression or ON after primary UKA. This approach demonstrates excellent mid-term functional outcomes and satisfactory implant survivorship, providing valuable evidence to support its role as a contemporary revision option Fixed-bearing implants for additional medial UKA are advised to eliminate the risk of bearing dislocations. In the absence of major complications, conversion to non-modular TKA components is feasible.

Level of evidence: Level IV.