Biomechanical Analysis of Limb Loads in Aided Gait Using Elbow Crutches

Abstract

The assumption that the resultant aid force is closely aligned to the shaft axis can cause considerable errors in analysis of elbow and shoulder loading . Therefore a pilot study incorporating a six-channel pylon in th {~} shaft of an elbow crutch and stick was carried out to determine the significance of off-axis loading . Three post-operative total hip replacement ( THR ) patients using elbow crutches , and one patient using sticks the following week were analysed . The peak off-axis values ranged from 1 . 1 to 2 . 5 degrees from the longitudinal axis of the shaft . These maxima occurred in the midcycle of loading and not in the initial and final stages of aid use where the loading might be expected to vary from the shaft axis . Theoretically , by ignoring a 2 . 5 degree off-axis orientation of the force , the location of the line of action at the shoulder ( l . 5m distance from aid-floor contact ) can be mislocated by 6 . 5 cm . This pilot study indicated the need to instrument the aid for the direction as well as the magnitude of the force in the elbow crutch and stick . Instrumentation A pair of height-adjustable aids were strain-gauged to measure the axial component and two shear components of the resultant force ( Figure 1 ) using a strain-gauged five quantity sensor made of HE 30 aluminium . This could be fitted to a walking stick or an elbow crutch handle : both of these could be adjusted for height . In each crutch four pairs of axial gauges record longitudinal load . The shaft was gauged for bending in two places a known distance apart and thus the shear forces were calculated from difference between the two bending outputs . Additionally the cuff portion of the elbow crutch was gauged in the anterior-posterior and medial-lateral planes to evaluate the contribution of the All of the connections to the five shaft channels and forearm to support .