New spatial mechanisms for kinematic analysis of the human knee and ankle joints

In virtually unloaded conditions, the tibiofemoral (knee) and tibiotalar (ankle) joints behave as single degree-of-freedom systems. In these conditions, fibres within the ligaments remain nearly isometric throughout the flexion arc and articular surfaces do not deform. Relevant theoretical models are showing that the ligaments and the articular surfaces act together as mechanisms to control the passive joint kinematics. In the knee joint, isometric fibres were identified within the ACL, PCL, MCL ligaments, whereas rigid contacts were associated to the two condylar articular surfaces. In the ankle, isometric fibres were identified within the calcaneal-fibular and tibio-calcaneal ligaments, rigid contacts were associated to the articular surfaces between the tibio-fibular mortise and the talus. Important enhancements have been achieved recently, with more accurate experimental data, more anatomical model surfaces, and more robust mathematical models. This would be useful for a more physiology-based comprehension of human diarthrodial joint motion.