Lower Limb Prostheses for Individuals Who Carry Infants, Toddlers, and Other Loads

The natural lower limbs provide important biomechanical functions such as body weight support, forward propulsion, and balance control during ambulation. When the loads borne by the lower limbs change, lower limb muscle activation responds accordingly to enable seamless continuation of biomechanical function. These loads can change suddenly, such as when carrying an infant, toddler, or other load like a heavy backpack. For individuals with a lower limb amputation, these sudden changes to weight-bearing loads can be problematic because they can negatively impact walking performance. One reason walking performance may suffer is that the properties of most prosthetic limbs, such as their stiffness, are constant and do not change to suit varying load conditions. Another reason is that the most widely prescribed prosthetic feet do not have motors, sensors, or brain-like controllers that act to replace the neuromuscular system of the amputated limb. Regardless of the reason, no evidence exists to guide prescription practice for veterans who walk with a prosthesis and experience sudden load changes.

The aim of this research is to identify the prosthetic foot that results in improved walking performance when individuals with lower limb amputation carry infants, toddlers, or other loads. The investigators will conduct a human subject experiment with help of twenty individuals with below-knee amputations. Study participants will walk on a treadmill with no added load and four added load conditions using a weighted pack (13.6 kg or ~30 lbs) to simulate an infant, toddler, or other load. The four conditions include the pack strapped to their front, their back, and carried with their arms on the intact limb side and the prosthetic limb side. Each participant will wear a usual prosthetic foot, this same foot with a heel-stiffening wedge, the same prosthetic foot but one category stiffness higher, a new-to-market dual keel prosthetic foot intended for load carrying situations, and a powered ankle foot prosthesis. The results from these experiments will aid clinicians in specifying the best prosthesis for individuals with lower limb amputations who frequently carry infants, toddlers, or other loads.

For individuals who wear a lower limb prosthesis while carrying infants, toddlers, or other loads, this research will provide evidence to support prosthesis prescription practice that reduces undesirable compensatory responses to load carriage. The objective is to help clinicians select among currently available solutions to enable individuals with lower limb loss to achieve their life and work goals.

Inclusion criteria

• Unilateral transtibial amputee
• Have been fitted with and used a prosthesis for at least six months
• Do not use heel stiffening wedges or bumpers in their as-prescribed prosthesis
• Wear their prosthesis for at least four hours per day
• Are moderately active by self-report
• Can be fitted with the study prostheses (prosthetic foot size, stiffness category and build heights)

Exclusion criteria

• Do not have a proper fit and suspension and one cannot be achieved with clinical resources
• Presence of disorder, pain, or injury other than amputation that interferes with gait