The effect of marker location variability on noninvasive canine stifle kinematics.

OBJECTIVE Evaluate the effect of marker placement on kinematics of the canine stifle in 3 distinct hindlimb models. STUDY DESIGN In vivo biomechanical study. ANIMALS Normal adult mixed-breed dogs (n=5). METHODS Ten retroreflective markers were affixed to the skin on the right rear leg of each dog to establish normal stifle kinematics. Four additional markers were placed around the greater trochanter (GT), 2 m cranial, caudal, dorsal, and ventral to evaluate single marker placement variability on kinematic model data. Dogs were walked and trotted 5 times through the calibrated space. Sagittal flexion and extension angle waveforms were acquired during each trial with 3 models that were produced simultaneously during each gait. The GT marker was reassigned to 1 of the 4 additional locations (cranial, caudal, dorsal, and ventral) to alter the kinematic model. Comparison of sagittal flexion and extension angle waveforms was performed with Generalized Indicator Function Analysis. RESULTS Each model provided consistent equivalent sagittal flexion-extension data. Analysis revealed statistically significant differences between all GT locations. The differences were greatest in the cranial and caudal locations for all models. CONCLUSIONS Deviation of the GT marker in the cranial/caudal direction from an anatomically normal position produces a greater degree of difference than deviation in a dorsal/ventral direction.