Asymmetry of mass and motion affects the regulation of whole-body angular momentum in individuals with upper limb absence

Background: There is a high fall prevalence in individuals with upper limb absence, which may be related to a momentum imbalance resulting from the loss of all or part of one arm. The purpose of this study was to characterise whole-body angular momentum in individuals with upper limb absence during walking, and determine the effect of restoring the mass and inertial properties of the impaired side with a mock prosthesis. Methods: Ten individuals with unilateral upper limb absence walked at self-selected speeds, with and without a mock prosthesis. For each condition, whole-body angular momentum range was computed during ten strides; in the first 50% of the stride bilaterally, and over the whole stride. Two-way repeated measures ANOVAs were used to assess the main effect of side and the interaction effect with prosthesis condition on the 50% range, and paired t-tests to determine the effect of prosthesis condition on the whole stride range (α = 0.05). Findings: Sagittal plane 50% range was greater for the sound compared to the impaired side stride (P = .003), with no difference in the coronal or transverse planes (P ≥ .8). Coronal plane whole stride range was lower when wearing the mock prosthesis (P = .021), with no change in the sagittal or transverse planes (P ≥ .5). Interpretation: Use of a prosthesis does not reduce a sagittal plane imbalance. There may be a greater risk of loss of balance in people with upper limb absence following a perturbation, particularly when it occurs during the sound side stance phase, during which whole-body angular momentum is elevated.