Achilles' tendon stretch during walking in hinged controlled ankle motion boots

Hinged controlled ankle motion boots are used to incrementally increase ankle joint range of movement during rehabilitation following Achilles' tendon rupture. This increased movement should induce mechanical stress on the tendon via cycles of stretching and shortening. However, research has yet to determine how this permitted range of movement influences tendon length change. Eight healthy individuals (age: 23 ± 2 y; stature = 1.70 ± 0.09 m; body mass = 67.7 ± 13.7 kg) walked at a self-selected speed on an instrumented, motorised treadmill in a hinged controlled ankle motion boot with three pre-established ankle ranges of movement: 0, 15, and 30°, which were all compared with walking in normal footwear. Kinematic and kinetic measurements were obtained using motion capture and the treadmill. Triceps surae mechanical characteristics, including Achilles' tendon stretch, were obtained with B-mode ultrasonography. Achilles' tendon stretch significantly (p < 0.001) increased as boot range of movement increased and was strongly correlated with measured ankle joint range of movement when the boot was set to a 15 or 30° range of movement (r ≥ 0.84, p ≤ 0.009). Increasing controlled ankle motion boot range of movement also increased ankle joint mechanical work done and total mechanical work done by the boot-wearing limb, which led to an increase in self-selected walking speed (all p < 0.001). These findings provide preliminary evidence that hinged controlled ankle motion boots have the capacity to provide a controlled mechanical stimulus to the Achilles' tendon when range of movement is increased. This has possible clinical application for the early management of Achilles' tendon rupture, potentially improving healing and functional outcomes if it can be translated into a patient population.