Association Between Posterior Ankle Soft Tissue Properties and Deep Squatting Ability After Ankle Fracture Surgery: A Cross-Sectional Study

Background: Deep squatting is essential for daily activities and sports; however, it is often limited after ankle fracture surgery, and the contributions of posterior ankle soft tissues, including the soleus muscle (SOL), Achilles tendon (AT), flexor hallucis longus muscle (FHL), and Kager’s fat pad (KFP), to this limitation remain unclear. This study aimed to determine the relationship between posterior ankle soft tissue properties (including stiffness and echo intensity [EI]) and deep squatting ability after ankle fracture surgery. Methods: This cross-sectional study included 53 patients (49.5 ± 16.1 years, 26 men) who underwent ankle fracture surgery. We measured the shear modulus of the SOL and AT, and the EI of the FHL and Kager’s fat pad; ankle range of motion and strength were evaluated. Deep squatting ability was also assessed. Multiple regression and receiver operating characteristic (ROC) analyses were performed to identify predictors of squatting limitation and evaluate discriminative performance. Results: Participants with a deep squatting limitation showed a higher shear modulus in the SOL and AT and higher EI in the FHL compared with those without limitations. SOL and AT shear modulus and FHL EI were significant independent predictors of ankle dorsiflexion angle during deep squatting. ROC analysis showed good discriminative ability for SOL shear modulus and AT shear modulus and modest discriminative ability for FHL EI. Conclusions: Increased stiffness and EI of the SOL, AT, and FHL were associated with reduced deep squatting ability after ankle fracture surgery. Targeted assessment and interventions addressing these tissues may improve postoperative function.