A computational study of the swing phase of the gait with standard and spring-loaded crutches

Crutches have suffered few functional modifications over their long history, with improvements largely limited to aesthetics and weight reduction aspects. The large energetic cost of the gait with crutches and problems associated to their long-term use impose a heavy burden to the users. In order to mitigate some of the mentioned problems, alternative designs have been proposed over the past few decades. Among them, the idea of incorporating an elastic element to the crutches to reduce impact forces transmitted to the upper extremities and to promote energy storage and release has been indicated in the specialized literature as a potential solution, in particular for the crutch gait styles more similar to the normative human gait such as the “two-point” and the “swing-through”. In fact, tendon elasticity has been shown to reduce energy consumption during animal and human locomotion by means of energy storage in the initial and mid stance-phase and release in the push-off phase of the gait cycle. In spite of the great potential of this idea, appropriate stiffness curves for the elastic element are poorly studied in the literature. This study aims at investigating appropriate stiffness values for the elastic element of spring-loaded crutches by means of computational simulations using a model of the swing phase of the “swing-through” gait style. The findings show that the stiffness should be tuned carefully to ensure improved gait quality. Spring-loaded crutches undoubtedly reduce impact forces transmitted to upper limbs and shoulder at touch down but they can deteriorate performance with respect to foot clearance and effort at the shoulder when compared to stiff crutches if stiffness is not carefully selected.