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

Background Acute 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. Purpose To 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. Methods A 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. Findings The 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. Interpretation Two years post-surgical repair, the Achilles tendon mechanical properties had not returned to the uninjured contralateral tendon values.