Effects of upper limb loss and prosthesis use on proactive mechanisms of locomotor stability.

Persons with upper limb loss (ULL) experience a high prevalence of falls, with the majority of falls occurring when walking. This issue may be related to altered arm dynamics, which play an important role in proactive mechanisms of locomotor stability. This study investigated effects of ULL and prosthesis use on proactive stability mechanisms, particularly if matching the mass and inertia of the impaired limb to the sound limb would enhance locomotor stability. Gait data were collected on adults with unilateral ULL during level walking while: (1) not wearing a prosthesis, (2) wearing their customary prosthesis, (3) wearing a mock prosthesis that matched the sound limb mass and inertia. Main and interaction effects of limb side and condition on trunk rotations, arm swing, step width, free vertical moment, and margin-of-stability were analyzed. Across conditions, arm swing, free vertical moment, and margin-of-stability were 2.27, 1.13, and 1.20 times greater, respectively, on the sound limb side than the impaired limb side. Persons with ULL display asymmetry in proactive mechanisms of locomotor stability with potentially greater medial-lateral stability on the sound limb side irrespective of prosthesis use, but heavier prostheses reduced the walking base of support. This bias may enhance fall risk on the impaired side if the prosthetic limb is used inappropriately to regain balance following a disturbance. Research is warranted to explore the consequences of this asymmetry on perturbation response.