Upper Limb Loss Perturbation Response

Recent investigations have suggested that persons with upper limb loss experience a high prevalence of falls with a quarter of reported falls resulting from a trip. Moreover, studies indicate that missing part of an arm may negatively impact balance and that use of a prosthesis exacerbates this problem. While the investigators are beginning to understand the effects of upper limb loss on balance, the understanding of how Veterans with upper limb loss respond to walking disturbances is incomplete. Therefore, the aims of this study are to observe the effects of upper limb loss and wearing a prosthesis on the preparation and recovery of Veterans who trip during walking. The investigators plan to use unique treadmill technology to deliver controlled, yet unexpected, perturbations to Veterans with upper limb loss and non-amputee controls, and assess walking stability through body dynamics. Results from this study will help us understand why Veterans with upper limb loss fall as a critical first step to addressing this problem through balance-targeted interventions that are integrated into patient care.

The primary aim of this pilot study is to characterize the proactive and reactive locomotor response of Veterans with upper limb loss (ULL) to a trip during walking. The investigators' recent VA-funded investigations have suggested that persons with ULL experience a high prevalence of falls and demonstrate postural control mechanisms that may impair stability. Specifically, nearly half of individuals with ULL at or proximal to the wrist level experience at least one fall per year and almost a third will experience two or more falls. Further, use of a prosthesis increases the likelihood of falling by six times, 25% of reported falls resulted from tripping, and nearly a third of individuals who experience a fall suffer a fall-related injury. Falls can have considerable economic burden on the VHA and lead to long-term diminished quality of life. The investigators' biomechanical studies suggest that persons with unilateral ULL display greater postural sway during standing than able-bodied individuals which increases when wearing a prosthesis, and right/left asymmetry in locomotor stability dynamics that may increase the risk of falling toward the impaired limb side and during sound limb side strides. These findings emphasize the need for additional research to better understand the mechanisms Veterans with ULL use to control balance and how wearing a prosthesis affects these strategies. As the investigators' previous research was concerned with steady-state characterization of postural control, the investigators now plan to build on this work by studying the effects of ULL and wearing a prosthesis on locomotor stability when responding to a trip disturbance during walking. In this context, locomotor stability is defined as the ability to recover from a perturbation and return to steady-state gait.

The investigators will address the study aims by analyzing trip-induced proactive and reactive locomotor strategy differences in two study comparisons: 1) Veterans with unilateral transradial level ULL against matched able-bodied controls (with and without one arm bound), and 2) Veterans with unilateral transradial ULL when wearing their customary prosthesis against not wearing their prosthesis. Controlled, yet unexpected, simulated trips will be delivered through the investigators' custom-built treadmill which permits programmable belt velocity disturbances and allows participants to continue walking following recovery. The investigators will characterize the proactive and reactive locomotor stability mechanisms through a set of biomechanical (angular momentum, arm and trunk kinematics) variables. Biomechanical variables will be quantified using an optical motion capture system. The investigators expect that Veterans with ULL will demonstrate altered locomotor stability mechanisms compared to controls, and these differences will exist between wearing and not wearing their customary prosthesis. Results from this study will help us characterize the underlying mechanisms of locomotor stability in Veterans with ULL and identify the factors associated with their increased prevalence of trip-related falls. Such knowledge is a critical first step to addressing this public health problem through stability-targeted rehabilitation interventions aimed at reducing falls, fall-related injuries, and associated VHA costs in this Veteran patient group. The investigators will use the outcomes from this pilot study to guide future VA Merit Award proposals to develop and assess physical training intervention methods and wearable and prosthetic technology to improve stability in Veterans with ULL. The VHA is an ideal venue to pursue this work as one of its main priorities is to elevate the standard-of-care for Veterans with limb loss.

Eligibility Criteria:
Inclusion Criteria:

Participant inclusion criteria for all participants include:

* age between 18 and 65 years
* normal or corrected vision
* able to walk unassisted for 20 minutes without undue fatigue or health risks

Additional inclusion criteria for participants with ULL include:

* unilateral ULL at the transradial level
* most recent major upper limb amputation occurred at least one year prior to study
* residuum and amputated side in good condition (no scars, infections, pain, etc.)
* habitual experience using an upper limb prosthesis for at least one year
* a self-reported comfortable prosthetic suspension

Exclusion Criteria:

Exclusion criteria for all participants include:

* self-reported additional neurological, vascular, or musculoskeletal pathologies (other than ULL when applicable) that may affect proprioception/balance
* self-reported medication that may affect proprioception/balance, e.g.:

  * drugs that are ototoxic, such as certain Aminoglycosides and pain killers
* cognitive deficits that preclude understanding of the study instructions
* presence of osteoporosis
* presence of pacemakers or stents that may be irritated by the chest harness