The structural and mechanical properties of the Achilles tendon 2 years after surgical repair

•Achilles tendon biomechanics was evaluated 2 years after surgical repair.•Tendon recovery was similar in early-mobilized patients and immobilized patients.•Patients' uninjured tendons were similar to tendons of healthy control subjects.•Two years after surgery injured tendons were more compliant than healthy tendons.

BackgroundAcute ruptures of the Achilles tendon affect the tendon's structural and mechanical properties. The long-term effects of surgical repair on these properties remain unclear.PurposeTo evaluate effects of early mobilization versus traditional immobilization rehabilitation programs 2 years after surgical Achilles tendon repair, by comparing force-elongation and stress-strain relationships of the injured tendon to those of the uninjured tendon.MethodsA group of males with previous Achilles tendon rupture (n = 18) and a group of healthy male controls (n = 9) participated. Achilles tendon rupture group consisted of patients that had received early mobilization (n = 9) and patients that had received traditional immobilization with a plaster cast (n = 9). Comparisons of tendon structural and mechanical properties were made between Achilles tendon rupture and healthy control groups, and between the uninjured and injured sides of the two rehabilitation groups in Achilles tendon rupture group. Ultrasound was used to determine bilaterally tendon cross-sectional area, tendon resting length, and tendon elongation as a function of torque during maximal voluntary plantar flexion. From these data, Achilles tendon force-elongation and stress-strain relationships were determined.FindingsThe Achilles tendon rupture group uninjured side was not different from healthy control group. Structural and mechanical parameters of the injured side were not different between the Achilles tendon rupture early mobilization and the immobilization groups. Compared to the uninjured side, the injured side showed a reduction in stress at maximal voluntary force, in Young's modulus and in stiffness.InterpretationTwo years post-surgical repair, the Achilles tendon mechanical properties had not returned to the uninjured contralateral tendon values.