Can motion of individual body segments identify dynamic instability in the elderly?

Objective. To determine if medio-lateral motion of the head, trunk, or pelvis demonstrates dynamic stability as well as whole-body center of mass during obstructed walking. Design. Group comparison of two elderly populations using whole-body motion analysis. Background. Detection of imbalance through analysis of center of mass motion is commonly adopted, requiring three-dimensional reconstruction of a multi-link biomechanical model. It would be advantageous clinically if similar detection could be made by analyzing segmental displacements of the pelvis, trunk, or head. Methods. Healthy elderly adults and elderly patients with balance disorders walked over level ground and crossed obstacles of height ranging from 2.5% to 15% of body height. Whole-body center of mass was calculated as the weighted sum of segmental centers of mass. Group differences in medio-lateral displacements and peak velocities of head, trunk, pelvis, and the center of mass were analyzed using a two-way image with repeated measures for obstacle height. Results. Elderly patients with balance disorders exhibited greater medio-lateral displacement and peak velocities of all segments. However, significant group differences were only detected in the center of mass displacement and peak velocity. Conclusion. Whole-body center of mass motion distinguishes elderly patients with balance disorders from healthy peers more consistently than markers representing the head, trunk, or pelvis. Large variation of individual segment motion makes dynamic stability difficult to assess. This study demonstrates that center of mass motion allows more sensitive detection of dynamic instability.