Restoration of pre-arthritic coronal alignment improves joint perception following fixed-bearing medial unicompartmental knee arthroplasty

Background The optimal postoperative alignment strategy in unicompartmental knee arthroplasty (UKA) remains a topic of debate. Although traditional mechanical alignment targets a neutral axis, restoring a patient's pre-arthritic, constitutional alignment may enhance clinical outcomes and joint perception. This study compares patient-reported outcomes (PROs) and joint awareness between patients who achieved pre-arthritic alignment and those who did not after medial fixed-bearing UKA. Methods In this retrospective cohort study, 266 patients who underwent medial fixed-bearing UKA between January, 2022 and May, 2023 were included, with a mean follow-up of 3.5 years. Pre-arthritic coronal alignment was estimated using the arithmetic Hip-Knee-Ankle angle (aHKA). Preoperative and postoperative coronal alignment measurements were performed using weight-bearing long-leg radiographs. Patients were stratified into two groups: pre-arthritically aligned (postoperative mechanical Hip-Knee-Ankle angle [mHKA] within ±3° of aHKA) and nonpre-arthritically aligned (mHKA beyond ±3° of aHKA). PROs assessed at final follow-up included Oxford Knee Score (OKS), Forgotten Joint Score-12 (FJS-12), and Kujala Score. Results Among the cohort, 212 knees (79.7%) were classified as pre-arthritically aligned and 54 (20.3%) as nonpre-arthritically Aligned. The groups were comparable in all baseline demographic and radiological parameters ( p > 0.05). However, the pre-arthritically aligned group demonstrated superior PROs: OKS (41.3 ± 5.4 vs. 39.2 ± 5.9, p < 0.05), FJS-12 (78.9 ± 2.3 vs. 71.1 ± 3.2, p < 0.05), and Kujala Score (85.4 ± 6.0 vs. 81.3 ± 5.5, p < 0.05). Conclusion Restoring pre-arthritic coronal alignment following fixed-bearing medial UKA is associated with superior patient-reported outcomes, including significantly better joint perception and patellofemoral function compared to nonpre-arthritic alignment. Further long-term follow-up is required to confirm the durability of these findings.