A Multimodal Exploration of Altered Mechanical and Histological Properties in Tendons with Degenerative Tendinopathy

Tendons injuries occur in people of all ages and can range from soreness and inflammation to full rupture requiring surgical repair. Larger injuries are typically preceded by accumulated damage that can change the strength of the tendon, and the way it responds to stress. A multimodal analysis of the changing properties serves to elucidate some of the changes both histologically and chemically, and how they affect the global properties like strength. Literature cites a number of changes including increased glycosaminoglycan (GAG) content, disordered collagen fibers, increased cellularity, increased cross-sectional area, and decreased Young’s Modulus. This paper analyzes these five altered characteristics using an in vitro loading protocol and a finite element computational model. GAG content, collagen disorder, and increased cellularity were evaluated experimentally in the lab using porcine tendons in which tendinopathic damage was induced. A changing GAG content was not observed in the end regions of these samples, but increased collagen disorder, tenocyte presence, and other histological evidence of micro tearing was examined and determined to be indicative of tendinopathic properties in the central region of the stretched samples, where the stress is thought to be the most highly focused. Highly variable local properties in tendinopathic tissues led to the creation of a computational model to address the impact of individual property changes. The model was created using the highly researched Achilles tendon, but is intended to be adapted in the future to represent the tissues used in our in vitro experiments to better analyze the impact of the changes on both global and local levels simultaneously. The representative model shows the effects of changing Young’s Modulus and Cross-sectional area