In vitro fatigue of human flexor digitorum tendons

Carpal tunnel syndrome and stenosing tenosynovitis (i.e., trigger finger) are common work-related musculoskeletal disorders (WMSDs) that have been linked to overuse of the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons of the hand. These injuries occur in response to repetitive loading; as such, they may be characterized using fatigue failure phenomenon. Current WMSD evaluation tools for carpal tunnel syndrome and trigger finger are built upon fatigue data from lower-limb tendons, however this may lead to inaccurate conclusions when assessing overuse injury risk at the wrist. Therefore, the purpose of this study was to characterize the fatigue behaviour of FDP and FDS tendons. We found that similar to other tendons, cyclically loaded FDP and FDS tendons illustrated a logarithmic relationship between applied stress and fatigue life, however the exact parameters of the FDP/FDS stress-fatigue life relationship were unique and may improve the accuracy of current carpal tunnel syndrome and trigger finger WMSD evaluation tools. We also observed that creep and damage rate had the strongest correlations with fatigue life, suggesting that these metrics may represent promising future directions for WMSD risk evaluation.