Injured Achilles Tendon Exhibits Inferior Mechanical and Structural Response During Fatigue Loading

Introduction Achilles tendon ruptures occur frequently and result in significant pain and disability with extensive recovery time. Since the Achilles tendon experiences repetitive loads at or near failure during normal activity, knowledge of tendon fatigue properties is critical for determining when patients may resume normal activity. Several studies have suggested the benefits of fatigue testing over traditional failure tests, such as the ability to detect subfailure damage accumulation and changes in structure with repetitive loading. Specifically, during fatigue loading, tissue stiffness initially increases and then gradually decreases as sub-rupture damage accumulates, followed by a dramatic increase in peak deformation prior to failure. While it is generally believed that injury affects the mechanical and structural response of tendon during fatigue loading, this relation has not yet been fully established. Therefore, the objective of this study was to examine the mechanical and structural properties of mouse Achilles tendon during fatigue loading following an acute injury. We hypothesized that an acute injury would dramatically decrease tendon mechanical and structural fatigue properties.