Double-Convex Peroneal Tubercle Morphology and MRI-Detected Peroneal Tendon Abnormality in a Non-Lateral Referral...

Background: The peroneal tubercle demonstrates substantial morphologic variability and may influence peroneal tendon mechanics. This study evaluated whether peroneal tubercle morphology and size are associated with MRI-detected peroneal tendon abnormality in patients undergoing ankle MRI for ankle pain without documented lateral malleolar/retromalleolar or peroneal tendon-specific symptoms. Methods: In this retrospective cross-sectional study, 487 ankle MRI examinations obtained between 2020 and 2023 were analyzed after excluding cases with lateral ankle/peroneal symptoms, clinically significant acute trauma, prior ankle surgery, or systemic inflammatory disease. Two orthopedic surgeons independently classified peroneal tubercle morphology (single-convex vs. double-convex) and measured tubercle height and anteroposterior length. Peroneal tendon abnormality was defined as MRI features consistent with tendinopathy and/or tenosynovitis. Inter- and intraobserver reliability were assessed using intraclass correlation coefficients and Cohen's kappa. Unadjusted associations were assessed using Fisher's exact test and point-biserial correlation. Multivariable logistic regression was performed to evaluate independent associations after adjustment for age, sex, BMI, and hindfoot alignment. Results: Mean age was 43.6 ± 15.6 years; 226 participants were male, and 261 were female. Peroneal tendon abnormality was present in 227/487 examinations (46.6%). Double-convex morphology showed a higher prevalence of abnormality than single-convex morphology (69.6% vs. 43.6%; unadjusted OR 2.97, 95% CI 1.63-5.41; p < 0.001). In the adjusted model, double-convex morphology remained independently associated with peroneal tendon abnormality (OR 2.85, 95% CI 1.52-5.34; p = 0.001). Tubercle height showed a modest independent association (OR 1.12 per mm, 95% CI 1.04-1.20; p = 0.002), whereas tubercle length was not associated (OR 1.008, 95% CI 0.981-1.036; p = 0.541). Reliability was excellent for tubercle height, tubercle length, and hindfoot alignment measurements and substantial to excellent for categorical ratings. Conclusions: In this non-lateral referral cohort, double-convex peroneal tubercle morphology was independently associated with higher odds of MRI-detected peroneal tendon abnormality. These findings reflect cross-sectional imaging associations rather than causation and should be interpreted with caution, given the heterogeneous MRI endpoint and the routine clinical MRI protocol.