Indications of unicompartmental knee arthroplasty and high tibial osteotomy would be different to achieve successful long-term outcome

BACKGROUND: Although both unicompartmental knee arthroplasty (UKA) and medial open-wedge high tibial osteotomy (MOWHTO) are widely accepted surgical options for medial compartment osteoarthritis, there is limited evidence from long-term outcomes to confirm and refine their established indications. This study aimed to evaluate the long-term clinical and radiologic outcomes of UKA and MOWHTO when performed according to their established indications at a single institution, and to characterize the demographic and preoperative radiographic differences associated with surgical selection. METHODS: Patients who underwent UKA or MOWHTO for medial compartmental OA with a minimum 10-year follow-up were retrospectively reviewed. Preoperative characteristics, including age and the degree of medial OA using Kellgren-Lawrence grading, clinical outcomes, and radiologic parameters, including hip-knee-ankle angle (HKAA), medial proximal tibial angle (MPTA), and OA progression in the patellofemoral compartment, were compared. Survivorship based on the conversion to total knee arthroplasty was also evaluated. RESULTS: The current study included 79 UKAs and 140 MOWHTOs with a mean 13.2 ± 1.7 years follow-up. Preoperatively, the UKA group had significantly older age (P < 0.001) and more advanced degree of medial OA (P < 0.001) than the MOWHTO group. Postoperative clinical outcomes were not significantly different between the groups. Radiologically, the UKA group had significantly less varus alignment and larger MPTA than the MOWHTO group (all, P < 0.001). Although the proportion of OA progression in the patellofemoral joint was higher in the MOWHTO group than in the UKA group at the latest follow-up (P = 0.012), there was no significant difference in anterior knee pain. At the mean 13-year follow-up, survival rates were not significantly different between the UKA (96.2%) and MOWHTO (98.6%) groups. CONCLUSIONS: Both UKA and MOWHTO demonstrated excellent long-term outcomes when performed under their established indications for medial compartment OA. Patients selected for UKA were older, had more advanced OA, less varus alignment, and a larger MPTA compared with those undergoing MOWHTO, consistent with published selection criteria. Radiographic progression of patellofemoral arthritis occurred more frequently after MOWHTO than after UKA, although this finding was not associated with clinical significance.