Spatial mechanisms for kinematic analysis of the 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 considerably. Relevant theoretical models show that ligaments and articular surfaces act together as mechanisms to control passive joint kinematics. In the knee, isometric fibres were identified within the ACL, PCL, MCL ligaments, and 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, and 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. The present results would be useful for a more physiology-based comprehension of human diarthrodial joint motion.