MR‐based in vivo follow‐up study of Achilles tendon volume and hydration state after ankle‐loading activity

The purpose of this study was to evaluate temporal alterations of the Achilles tendon volume and hydration state after cross‐country‐running. Achilles tendons of six untrained participants were examined on a 3T MR‐scanner before running, immediately afterwards, and in the following 24, 48, and 72 h. Using a 3D‐UTE sequence, caudal (CA) and cranial (CR) mid‐portion tendon areas were examined with off‐resonance saturation ratios (OSR) and T2* relaxation times. Tendon volume was measured with a self‐written Matlab‐based automated contour detection algorithm (AVAT) in submillimeter T2‐weighted MR images. A significant influence of running in caudal (P = 0.017) and cranial OSR values (P = 0.001), tendon volume (P = 0.024), and cranial T2* measurements (P = 0.046), but not in caudal T2* values (P = 0.298) were found. In detail, mean individual OSR and tendon volume measurements demonstrated a similar but inverted course in their values after exercise: initially, OSR values increased after running (and tendon volume decreased), while subsequently a decrease of OSR values (with an increase of tendon volume) could be observed. OSR and tendon volume measurements are able to detect a physiological response of tendons to a mechanical stimulus. After a transient decrease of free water in the Achilles tendon, an increase with a maximum free water content 48 h after ankle loading and a tendency toward normalization after 72 h was found.