Comparison of stance phase knee joint angles and moments using two different surface marker representations of the proximal shank in walkers and runners.

Efforts to compare different surface marker configurations in 3-dimensional motion analysis are warranted as more complex and custom marker sets become more common. At the knee, different markers can been used to represent the proximal shank. Often, two anatomical markers are placed over the femoral condyles, with their midpoint defining both the distal thigh and proximal shank segment ends. However, two additional markers placed over the tibial plateaus have been used to define the proximal shank end. For this experiment, simultaneous data for both proximal shank configurations were independently collected at two separate laboratories by different investigators, with one laboratory capturing a walking population and the other a running population. Common discrete knee joint variables were then compared between marker sets in each population. Using the augmented marker set, peak knee flexion after weight acceptance was less (1.2-1.7°, P < .02) and peak knee adduction was greater (0.7-1.4°, P < .001) in both data sets. Similarly, the calculated peak knee flexion moment was less by 15-20% and internal rotation moment was greater by 11-18% (P < .001). These results suggest that the calculation of knee joint mechanics are influenced by the proximal shank's segment endpoint definition, independent of dynamic task, investigator, laboratory environment, and population in this study.