ERRORS IN ESTIMATING TIBIAL TRANSLATION DURING NATURAL CADENCE WALKING
KURT T. MANAL, Irene S. McClay · Medicine & Science in Sports & Exercise · 2001
The anterior cruciate ligament (ACL) is the prime passive restraint opposing excessive anterior tibial translation relative to the femur. Excessive translation can result in a knee posture that is mechanically unstable and may result in the ACL deficient individual giving-way. The mechanical events associated with giving-way are not well understood. However, excessive translation is believed to be a major contributing factor. Locating the proximal end of the tibia is necessary when measuring relative translation between the tibia and femur. The goal of this project was to investigate the precision with which the proximal end of the tibia could be located in 3D-space from tracking targets attached to the shank using standard video-based motion analysis. To this end, a percutaneous skeletal tracker (PST) was secured to the distal tibia for each of 7 subjects. The PST tracking targets were assumed rigid with the tibia and not affected by soft tissue movement of the shank. In addition, surface mounted tracking targets (SMT) were collected at the same time as the bone-anchored PST targets. A 6 camera Vicon Motion analysis system (60 Hz) and a Bertec force platform (240 Hz) were used to collect target trajectories and force records. Three natural cadence walking trials were processed for each subject. Subjects walked along the Y-axis of the laboratory fixed inertial reference, with the Z-axis directed superiorly. Translations along the Y axis are the most relevant in the context of this study (i.e., analogous to antero-posterior translation). Mean differences in the range of translations using the SMT and PST tracking targets across all subjects was 9.7, 8.3 and 4.1 mm along the X, Y and Z axes respectively. The absolute smallest within-subject differences were 4, 4 and 1 mm along the X, Y and Z axes. Note that these differences represent the smallest values along each axis and were not necessarily for the same subject. Likewise, differences as large as 17, 15 and 8 mm were noted along the X, Y and Z axes. The results of this study suggest the precision with which the proximal end of the tibia can be located using surface mounted tracking targets and standard motion analysis methods is not acceptable for accurately defining tibial translation during natural cadence walking.