Biomechanical and Viscoelastic Properties of the Ankle Muscles in Relation to Muscle Force in Patients with Operated Tibial Pilon Fractures

Background: Tibial pilon fractures are complex injuries frequently associated with persistent functional impairment, even after successful surgical fixation. While previous studies have reported deficits in muscle strength and balance, little is known about the side-to-side variations in intrinsic biomechanical and viscoelastic muscle properties following surgery. Objectives: This study aimed to compare the biomechanical and viscoelastic properties of ankle periarticular muscles between the affected and non-affected limbs in patients with surgically treated unilateral tibial pilon fractures. A secondary objective was to evaluate the relationship between intrinsic muscle properties and isometric muscle force. Methods: A total of 39 subjects with unilateral surgically treated tibial pilon fractures were evaluated after fracture healing. Myotonometric assessment was performed to evaluate muscle mechanical parameters, including tone (frequency), stiffness, and elasticity (decrement), as well as viscoelastic properties, including relaxation time and creep, in the tibialis anterior, peroneus longus, medial gastrocnemius, and lateral gastrocnemius muscles. Isometric muscle force of ankle dorsiflexors and plantar flexors was measured using a handheld dynamometer. Side-to-side comparisons and Pearson correlation analyses were performed. Results: The affected limb showed significantly reduced ankle range of motion in all planes and significantly lower isometric muscle force in both the dorsiflexors (p = 0.0002) and the plantar flexors (p = 0.0066). Stiffness was significantly higher in the medial (p = 0.038) and lateral gastrocnemius (p = 0.045) muscles on the affected side. Decrement was significantly increased (indicating reduced elasticity) in the peroneus longus (p = 0.021). No significant differences were observed for tone, relaxation time, or creep. Conclusions: Myotonometry revealed increased stiffness in the gastrocnemius muscles and reduced elasticity in the peroneus longus on the operated side compared with the non-affected limb. Tone and viscoelastic properties did not differ significantly between sides. However, tone, stiffness, and elasticity were significantly correlated with muscle force, indicating a relationship between intrinsic muscle mechanical properties and force production after tibial pilon fracture surgery.