Novel single marker approach to estimation of lower extremity movement.

Sacrum motion is used extensively in studying the biomechanical characteristics of walking. This study aimed at investigating the potential of sacrum motion to provide an estimation of important gait events in conjunction with predicting the motion of lower extremity segments. Three-dimensional trajectories of 37 reflective markers placed on anatomical landmarks of 14 healthy subjects were recorded while walking at self-selected normal walking speed on treadmill. Elevation angles of lower extremity segments in sagittal plane were estimated using the lower extremity markers. Regression analysis was used to estimate the ability of sacrum kinematic variables to predict lower extremity elevation angles. Prediction was performed at 10 different gait events extracted from three-dimensional sacrum trajectories. The coefficients of the predicting variables were analyzed at these events. The results indicated that heel strike and toe off event instances identified using trajectory of sacrum marker were close to the results of accurate kinematic methods. Additionally, the motion of this point was able to predict lower extremity angles with a suitable coefficient of determination at early single support and mid-swing events. A range of musculoskeletal disorders could be identified using the elevation angles at these events. This study could be considered as a step toward development of effective and simplified instrumentation in clinical diagnosis of gait disorders.