Silent mechanical adaptation: Passive mechanical properties of ankle-surrounding tissues in individuals with unilateral chronic ankle instability

Background Chronic ankle instability (CAI) is a complex condition characterized by recurring sprains. Objective Our study aimed to compare the tone, stiffness, and elasticity of the periarticular muscles, Achilles tendon (AT), and plantar fascia (PF) between the affected and non-affected limbs of individuals with unilateral CAI. Methods The cross-sectional study included 75 volunteers aged 18 to 45 years who had been diagnosed with CAI by a physician. Ankle instability was assessed using the Identification of Functional Ankle Instability (IdFAI). Passive mechanical properties (PMP), including frequency, stiffness, and logarithmic decrement, of the tibialis anterior (TA), peroneus longus (PL), medial and lateral gastrocnemius (MGC – LGC), AT, and PF were assessed bilaterally using the MyotonPRO. PMP were compared between sides, and relationships between IdFAI scores and PMP on the affected side were examined. Results The mean age was 27.46 ± 4.23 years. Logarithmic decrement and stiffness values were higher on the affected side in the TA (p = 0.011, p = 0.027), PL (p = 0.017, p = 0.031), and PF (p = 0.020, p = 0.028) compared to the non-affected side. Logarithmic decrement was also higher in the MGC (p = 0.029) and LGC (p = 0.005). No significant difference in frequency was observed for any of these structures (p > 0.05). The AT showed no significant differences in frequency, stiffness, or logarithmic decrement between the affected and non-affected sides (p > 0.05). Conclusions CAI is a multidimensional pathology characterized by deterioration of the PMP of the surrounding muscles and PF. These findings suggest that management of CAI should include interventions aimed at improving myofascial tissue elasticity in addition to neuromuscular rehabilitation. Trial registration: ClinicalTrials.gov, TRN: NCT06987435.