Vertical Displacement of the Center of Mass during Spring-loaded Crutch Ambulation

Approximately 600,000 Americans use crutches each year [1]. A relatively novel spring-loaded crutch design is now being marketed (Figure 1A). The manufacturer (Millennial Medical Inc, Logan, UT, USA) of this crutch design has speculated that because a spring located in the crutch post compresses during crutch-ground contact, crutch length decreases, and less vertical displacement of the whole-body center of mass (COM) may occur during each crutch-ground contact phase of crutch ambulation. Although this idea is somewhat intuitive, it has not yet been evaluated objectively. Decreasing vertical displacement of the COM during crutch ambulation may be important, as it could decrease mechanical work that is performed on the COM and contribute to decreased metabolic energy expenditure during crutch ambulation; increased metabolic energy expenditure is a major challenge for habitual crutch users [2].