Patellar tracking during the gait cycle.

PURPOSE To assess normal patellar tracking during walking using the 9-camera infrared system. METHODS Four men and 6 women aged 25 to 33 (mean, 29) years each performed 16 walking trials on one occasion. They had prominent patellae with minimal soft tissues (minimising skin artefacts), and their knees and lower limbs were normal and symmetrical. 12 retro-reflective markers (2.5 cm in diameter) were taped to anatomic landmarks of the lower body. Two additional markers (1.4 cm in diameter) were first placed on the medial and lateral points and then proximal and distal points of the patella. Patellar motion relative to the centre of the knee joint was defined as angles between the centre of the knee joint and the 2 sets of patellar markers (medial-lateral and proximal-distal). The mean, maximum, and minimum values of these angles in a standing position were recorded, as was patellar tracking during walking. The X, Y, and Z coordinates for each marker were smoothed out throughout the capturing time. A single gait cycle per trial was chosen for analysis. RESULTS During walking, the centre of the knee joint and the patella did not move in unison, and the extent of separation was subject dependent. In 70% of the participants, the maximum angle between the centre of the knee joint and each set of markers occurred in the swing phase (0-43%) of the gait cycle. When analysing both sets of markers together, the percentage of participants became 60%. The extent of knee flexion was subject dependent. There was more medial-lateral motion (shift) of the patella than proximal-distal (tilt) motion during the gait cycle. These indicated that the maximum amount of patellar shift and tilt occurred in the swing and early stance phases of the gait cycle and that abnormal patellar motion can be detected if excessive shift or tilt occurs outside of these phases. CONCLUSION Patella mal-tracking could be attributed to the position of the lower body segments rather than the absorption or generation of forces.