ACL Biomechanics

Biomechanics, i.e., the observation of biological systems from a mechanical perspective, is typically described through kinetics and kinematics. While the term kinetics refers to the relationship between motion and its causes, specifically forces and torque, kinematics describes the 3-dimensional geometry of a motion regarding displacement, acceleration and velocity. The composition of a ligament defines its kinetic properties, e.g. maximal load to failure and young’s modulus. The kinetic properties and orientation of a ligament have implications for joint kinematics. The inherent biomechanics of the knee joint are complex and not yet fully elucidated. As a result, there is conflicting evidence in the literature concerning the biomechanical function and nature of the ACL. Historically, the function of the ACL is simplified to the restrain of anterior tibial translation and internal tibial rotation. However, the ACL is also thought to be involved in the stabilisation and centralisation of rotational axes as well as the balance of stability while allowing a variable degree of physiological rotatory laxity. Indisputable, however, is the fact that the ACL is of paramount importance for knee biomechanics, which is reflected in the fact that ACL transection is used to reliably induce osteoarthritis in experimental animal studies.