The Biomechanics of the Anterior Cruciate Ligament and Its Reconstruction

The anterior cruciate ligament (ACL) continues to be a major topic in orthopaedics and biomechanics. This is due to the high incidence of injury and its disabling consequences. That the disabling consequences have not yet been completely overcome guarantees continued interest. Injury to the ACL is associated with a range of problems, such as pain, instability, meniscal damage and osteoarthritis (Noyes et al., 1983; Segawa et al., 2001). This can be due to injury to other structures at the time of ACL injury, e.g. meniscus and articular cartilage, as well as developments secondary to the initial injury (Segawa et al., 2001). Although isolated injury to the ACL is considered uncommon, surgical transection of the ACL induces cartilage degeneration so reliably it is used to induce osteoarthritis in experimental animals (Desrochers et al., 2010). Simple repair is effective for some ligaments, but such repair of the ACL has had poor results, and the orthopaedic world currently awaits the development of a useful scaffold that can be placed between the torn ends of the ligament to promote effective healing (Murray, 2009). In the interim a popular choice of treatment with positive results is surgical reconstruction (replacement), using a graft fashioned typically from the patellar ligament or from hamstring tendons (Woo et al., 2002). But despite positive outcomes from ACL reconstruction problems still persist after ‘successful’ surgery, especially osteoarthritis (Øiestad et al., 2010). It is only possible to speculate that kinematic differences that remain after, or are caused by, surgical reconstruction lead to osteoarthritis (Scanlan et al., 2010), but post-surgical kinematic differences may lead to cartilage loading differences, which then predispose the knee to osteoarthritis (Andriacchi et al., 2004, 2006). These loading differences may lead to cartilage areas subsequently sustaining higher or lower loads or loads of a different nature (e.g. tension, compression) (Chaudhari et al., 2008). Development of a suitable ligament substitute is a straightforward matter: (1) determine the nature of the ligament, and (2) design a replacement that replicates this nature tolerably