Evaluation of Strain in Human Flexor Digitorum Profundus and Flexor Digitorum Superficialis Tendons Under Different Ex Vivo Loading Modalities

Abstract

Tendon is an integral part of the musculoskeletal system. Improving our understanding of tendon properties can be useful for further developing musculoskeletal injury risk assessment models. This dissertation provides fundamental data on the mechanical properties of human tendons of the hands and wrist through ex vivo testing. This was accomplished through first determining the most common/appropriate methods to measure and test tendons. Human tendons from 14 donors ranging in age (30 - 77 years old) were used in the described studies. Tendons from these donors were exposed to either cyclic fatigue, creep, or sequence loading (combined loading) until failure. Results of these studies found that strains at failure of (8 - 22%) were consistent with known literature (8 - 20%) suggesting that tendon is similar in how strain develops regardless of anatomical location or tendon type. Though the strains at failure were within the above expected range, average times to failure varied (0.26 - 29.53 hrs.) depending on the test. A dependent relationship between applied stress and time to failure was also observed. Differences were found in creep times to failure when comparing tendons of the hands and wrist to the Achilles tendon. A statistically significant transition effect was found in combined loading to which in both levels of ultimate tensile strength (25 and 55%) transitioning from cyclic to creep resulted in an average difference in strain of 0.4% and 0.34% than if transitioning from a creep load to a cyclic load. The presence of a transition effect does not suggest that creep load results in more damage than cyclic, but instead shows slightly larger changes in strain when transitioning. Improving our understanding of the ex vivo viscoelastic properties of tendon provides fundamental data to improve injury risk assessment models.