Differences in ankle-joint complex motion during the stance phase of walking as measured by superficial and bone-anchored markers.

Bones of the ankle-joint complex are difficult to represent with superficial markers and an invasive approach is required to quantify skin movement artifact. Three-dimensional coordinates during gait were first calculated from sets of three superficial markers located on both the lower leg and heel. Intracortical pins equipped with external marker arrays were subsequently inserted in the tibia, talus and calcaneus for further trials. Tibiocalcaneal and talocalcaneal joint helical axis component rotations were calculated. Intersubject motion patterns were comparable. Root mean square (RMS) differences were chosen to describe discrepancies between temporal intracortical pin and superficial marker curves. Results for the tibiocalcaneal rotations inversion/eversion, plantarflexion/ dorsiflexion and abduction/adduction were 2.5 degrees, 1.7 degrees and 2.8 degrees respectively. Inversion/eversion about the talocalcaneal joint showed an RMS difference of 2.1 degrees. A systematic over- or underestimation of superficial relative to bone-anchored markers could not be determined.