Repeatability of kinematic data of the foot and ankle in gait

In this study, we standardized three-dimensional motion analysis of the foot and ankle using external landmarks and presented a comprehensive repeatability within a test day and between test days using statistical measures of similarity of waveforms. A three-segment rigid body model, the tibia, hindfoot, and forefoot (metatarsals), was used to represent the foot and ankle. Two marker sets, bony landmark set and marker trials, were used simultaneously. A motion analysis system was used to collect the three- dimensional trajectories of markers. Ten normal subjects were evaluated three times on each test day and on three different test days while walking at their preferred or natural speed. Using the landmarks, three-dimensional kinematics could be determined. Then statistical measures were used to evaluate repeatability of Euler angles of the ankle (hindfoot relative to tibia) and midtarsal (forefoot relative to hindfoot) joints of the foot. For ankle joint angles, the marker triad is slightly more reproducible than the bony landmark set. For midtarsal joint angles, bony landmark set is better than marker triads. The results suggest that it may be reasonable to base significant clinical decisions on the results of a single foot kinematic evaluation.