Mechanics of damage in biological soft tissues

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Knee ligament injuries are common, in fact, 1 in 3000 people suffer an injury to their anterior cruciate ligament (ACL) every year. Ligaments are soft biological tissues that connect bones across a joint. Knee ligaments guide joint motion and maintain joint stability by resisting forces that tend to separate the bones of the joint. Some ligaments heal after injury by producing scar tissue that reconnects the torn ligament ends. When ligaments are not able to heal and reconnect the torn ligament ends, surgery is required to reconstruct the injured ligament. In some percentage of patients, injured and reconstructed ligaments do not maintain joint stability and appear to have "stretched out", leaving the patient susceptible to the development of painful osteoarthritis. Unfortunately, the reasons for poor healing of ligaments remain unclear. However, the current proposal questions whether the healing process is able to keep pace with the mechanical demands placed on the ligament. If the mechanical demands exceed the healing potential, damage may accumulate in the ligament as it heals. Normal daily loading for ligament involves sustained and repeated loading; the engineering terms for which are creep and fatigue, respectively. Creep and fatigue loading can cause damage to accumulate in a healing ligament. The exciting innovation of the proposed study is to apply the established engineering principles of continuum damage mechanics to a new problem from the field of biology and medicine, which is poor resolution of ligament healing. Experimental mechanical tests and theoretical mathematical models will be applied to help engineers and orthopaedic surgeons alike understand how damage accumulates in healing ligaments. The intended benefit of this research program is improved treatment of patients with knee ligament injuries.