Differential effects of tibia varus deformity on clinical outcomes following high tibial osteotomy and unicompartmental knee arthroplasty for moderate medial compartment osteoarthritis with moderate varus alignment

Abstract

Introduction: There is a lack of clinical evidence supporting the decision-making process between high tibial osteotomy (HTO) and unicomparmental knee arthroplasty (UKA) in gray zone indication, such as moderate medial osteoarthritis with moderate varus alignment. This study compared the outcomes between HTO and UKA in such cases and assessed the risk factor for not maintaining clinical improvements.

Materials and methods: We retrospectively reviewed 65 opening-wedge HTOs and 55 UKAs with moderate medial osteoarthritis (Kellgren-Lawrence grade ≥ 3 and Ahlback grade < 3) and moderate varus alignment (5°< Hip-Knee-Ankle angle < 10°) over 3 years follow-up. Confounding factors including patient demographics, postoperative lower limb alignment was assessed. Dummy variable was used to categorize the HTO and UKA according to presence of tibia varus deformity (medial proximal tibial angle of 85°). Clinical outcomes were measured using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score preoperatively, 1 year postoperatively, and at the last follow-up. Cox regression analysis identified risk factors for not achieving minimal clinically important differences (MCID) in WOMAC scores.

Results: The WOMAC score at 1-postoperative year significantly improved beyond MCID in all UKA and HTO. However, over a mean follow-up of 68.7 months (HTO) and 64.3 months (UKA), 16 patients (13.3%) experienced clinical deterioration. Notably, patients with suboptimal postoperative alignment, those undergoing HTO without tibial vara, and UKA with tibial vara had higher risks of clinical deterioration during the mid-term period.

Conclusion: Tibial varus deformity differentially affects clinical outcomes after HTO and UKA in moderate medial compartment osteoarthritis with moderate varus alignment. Clinicians should consider the deformity's origin when selecting treatment for this patient, as certain combinations (HTO without tibia vara and UKA with tibia vara) are associated with increased risk of not maintaining mid-term clinical improvements.

Keywords: High tibial osteotomy; Osteoarthritis; Tibial deformity; Unicompartmental knee arthroplasty.