Patients with Achilles Tendinopathy Show Reduced Intratendinous Sliding during Dynamic Exercises.

Abstract

Intratendinous sliding, that is, nonuniform motions between the superficial and deep layers of the Achilles tendon, is reduced in individuals with Achilles tendinopathy compared with healthy controls during isometric contractions. Previous work has shown that intratendinous sliding can be increased by performing isometric contractions with a horizontally outward-rotated ("toes-out") foot position. The purpose of this study was to compare intratendinous sliding between healthy individuals and patients with Achilles tendinopathy during dynamic exercises, and to determine the effect of a toes-out foot position. Forty participants (20 healthy and 20 Achilles tendinopathy) performed dynamic exercises, including bilateral heel rise/drop (sitting and standing), unilateral heel rise/drop (knee extended and bent), and squat. Exercises were performed in a neutral and toes-out foot position, with ultrasound images captured using an external probeholder. Intratendinous sliding (mm) was estimated via a speckle tracking algorithm as the difference between displacement of the superficial and deep layers of the Achilles tendon. Main effects of group, foot position, and exercise were found, indicating that Achilles tendinopathy patients have reduced intratendinous sliding, that intratendinous sliding can be increased in a toes-out foot position, and that some exercises induce more intratendinous sliding than others. These findings support intratendinous sliding as a marker of tendon health and suggest that foot positioning may be a simple way to enhance sliding. Given the poor rehabilitation outcomes for Achilles tendinopathy patients, implementing an external foot position during rehabilitation protocols could offer a low-cost and easy-to-implement method to improve rehabilitation success rates.