Biomechanical model of knee collateral ligament injury with six degrees of freedom.

Knee ligament injuries cannot be fully described using simplified joint models or by experimentation alone. The study objective was to model the contributions of the collateral ligaments over six degrees of freedom (DOF) of knee joint articulation to aid the diagnosis of knee ligament injuries. A kinematic model of the knee joint with six DOF was developed using the Musculoskeletal Joint Modeller software, and the effects of medial collateral ligament (MCL) and lateral collateral ligament (LCL) rupture were evaluated. The centres of mass of the tibia and femur were determined from their surface geometry, and the displacement of the moving tibia was determined by measuring the displacements of the attached ligaments with respect to its centre of mass. Compared to an intact knee, a tibia without the LCL had higher medial translation and lower valgus rotation, while a tibia without the MCL had higher lateral translation and higher valgus rotation. At 0°, 30° and 60° of flexion, the tibia without the LCL had more internal rotation than an intact knee. Understanding the complete kinematics of knee joints may improve the diagnosis of ligament injuries and guide tissue replacement surgery. Predicting joint behaviour in the clinic after treatment might benefit from a combined modelling approach that includes both clinicians and basic researchers.