Nonoperative, Dynamic Treatment of Acute Achilles Tendon Rupture: Influence of Early Weightbearing on Biomechanical Properties of the Plantar Flexor Muscle–Tendon Complex—A Blinded, Randomized, Controlled Trial

Acute Achilles tendon rupture alters the biomechanical properties of the plantar flexor muscle–tendon complex that can affect functional performance and the risk of repeat injury. The purpose of the present study was to compare the biomechanical properties of the plantar flexor muscle–tendon complex in patients randomized to early weightbearing or non-weightbearing in the nonoperative treatment of Achilles tendon rupture. A total of 60 patients were randomized to full weightbearing from day 1 of treatment or non-weightbearing for 6 weeks. After 6 and 12 months, the peak passive torque at 20° dorsiflexion, the stiffness during slow stretching, and the maximal strength were measured in both limbs. The stiffness of the plantar flexor muscle–tendon complex in the terminal part of dorsiflexion was significantly increased (p = .024) in the non-weightbearing group at 12 months. The peak passive torque was significantly lower for the affected limb at 6 months (91%; p = .01), and the stiffness was significantly lower for the affected limb during the early part of dorsiflexion at 6 (67%; p < .001) and 12 (77%; p < .001) months. In conclusion, an increased stiffness of the plantar flexor muscle–tendon complex in the terminal part of dorsiflexion was found in the non-weightbearing group. The altered stiffness and strength in the affected limb could affect the coordination of gait and running.