Three-dimensional bone kinematics in an anterior laxity test of the ankle joint.

Questions addressed in this in-vitro study are (1) what are the actual three-dimensional kinematics of talus and calcaneus during an anterior drawer test as performed with the quasi-static anterior ankle tester (QAAT) (2) does laxity measurement with the QAAT represent the true anterior translation of talus relative to the tibia? Simultaneous measurements were made with the QAAT and a three-dimensional kinematics analysis system in five specimens. The three-dimensional translations and rotations on three axes were analysed at 25, 50 and 100 N of applied anterior load, with increased ligament damage. For four out of five remaining specimens, anterior translation values of talus and calcaneus and values as measured with the QAAT show a significant increase with growing ligament damage and with higher loads. Skeletal motions of talus and calcaneus show great similarity in three different motion axes, with increased ligament damage and at any given load. Skeletal translations and rotations of talus and calcaneus show great similarity during an anterior drawer movement of the ankle joint. Anterior skeletal translation of the talus and calcaneus show fair correlation with the anterior displacements measurements of the QAAT. These QAAT measurements show an overestimation of the laxity value by more than 200% irrespective of the load applied.