Application of Acoustoelasticity: Identifying Tendon Damage

Damage to connective tissue such as tendons can occur via stretch injuries. During stretch injury, a tendon experiences permanent subfailure damage. Provenzano et al. showed that irreversible damage to the cellular structure of tendon or ligament occurs before noticeable changes can be measured in the mechanical behavior of the tissue [1]. The same paper also showed that during loading a portion of the curve can be classified as a sub-damage region where repeated loading in that range will have no effect on mechanical properties. There is also a damage region where plastic deformation and fiber tearing occurs. In this region, the severity of damage increases as the amount of strain increases. For the same level of functional loading after damage, tissue stiffness decreases while tissue strain increases. In-vivo measurements of damage indicators, such as strain and stiffness of a tendon, prove difficult using current techniques, since many of those methods are invasive (implanted strain gages) or large and non-portable (MRI)[2]. Recent studies have shown that ultrasound can be employed to assess ligaments and tendons by measuring ultrasound wave velocity and echo reflection [3,4].