Prevalence and Associated Factors of Ankle Osteoarthritis in Achondroplasia: A Retrospective Radiographic Assessment of 134 Patients.

Objective: The primary aim of this study is to examine the prevalence of ankle osteoarthritis in patients with achondroplasia and to assess the impact of surgical correction of lower limb alignment on this prevalence. The secondary aim is to identify radiographic parameters associated with ankle osteoarthritis.

Design: This retrospective cohort study included 134 patients (268 ankles) who visited our institution between March 2014 and February 2023. Lower limb alignment was assessed using the mechanical axis deviation, lateral distal tibial angle, anterior distal tibial angle, and talar tilt angle. Ankle osteoarthritis was evaluated using the Van Dijk Osteoarthritis score and modified Kellgren-Lawrence (K-L) scale by 2 experienced orthopedic surgeons.

Results: The prevalence of ankle osteoarthritis in our study cohort was 29%, and that of advanced ankle osteoarthritis defined by Van Dijk Osteoarthritis scale III or modified K-L grade 4 was 0.8% (aged <40 years, 22%, and 0%; aged ≥40 years, 42% and 2%, respectively). Talar tilt angle was the only radiographic parameter that showed a significant correlation with the degree of ankle osteoarthritis (Van Dijk Osteoarthritis score, r_s = 0.403, P < 0.001; modified K-L grade, r_s = 0.385, P < 0.001).

Discussion: The prevalence of ankle osteoarthritis in achondroplasia is moderate, but the progression to advanced stages is uncommon. Ankle osteoarthritis in achondroplasia is strongly associated with increased talar tilt angle. This finding emphasizes caution regarding ankle osteoarthritis in achondroplasia with a nonparallel tibiotalar articular surface. Clinicians should, therefore, consider regularly assessing the talar tilt angle in patients with achondroplasia.