Balance recovery mechanisms used by below-knee amputees following mediolateral perturbations
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Lower limb amputees have a higher risk of falling compared to non-amputees. Proper regulation of whole-body angular momentum is necessary in order to prevent falls and is particularly important in the frontal plane as humans are most unstable in the mediolateral direction while walking. However, the balance recovery mechanisms used by lower limb amputees when recovering from a fall are not well understood. The purpose of this study was to understand the neuromuscular balance recovery mechanisms used by lower limb amputees in response to mediolateral balance perturbations by examining changes to frontal plane whole-body angular momentum, hip joint work, and ankle joint work. Ten amputees and 12 non-amputees participated in this study where an unexpected, repeatable lateral or medial perturbation disturbed the placement of the perturbed limb immediately prior to heel strike on the residual, sound or non-amputee limbs. Lateral perturbations of all limbs resulted in a reduced range of whole-body angular momentum (p=0.0048 for residual limb, and p<0.0001 for sound and non-amputee limbs) and increased positive frontal plane hip work for lateral perturbations of all limbs (p=0.0239 for the residual limb, p<0.0001 for both sound and non-amputee limbs). Medial perturbations for all limbs (p = 0.0030 for residual limb, p < 0.0001 for sound and non-amputee limbs) resulted in increased range of whole-body angular momentum and decreased positive frontal plane hip work (p < 0.0001 for all limbs). Medial perturbations of the sound (p = 0.0055) and non-amputee (p < 0.0001) limbs also resulted in an increase in the positive frontal plane ankle work. These results suggest that medial foot placement perturbations are particularly challenging to maintain balance and that hip and ankle strategies play an important role when recovering balance. Thus, rehabilitation interventions that focus on the hip and ankle muscles to regulate mediolateral balance, particularly the hip abductors and ankle plantarflexors, and use of prostheses with active ankle control may reduce the risk of falls.