Background Deficits in balance control are one of the most common and serious mobility challenges facing individuals with lower limb loss. Yet, dynamic postural balance control among indivdiuals with lower limb loss remains poorly understood. Here we examined the kinematics and kinetics of dynamic balance in individuals with unilateral transtibial limb loss. Methods Five individuals with unilateral transtibial limb loss, and five age- and gender-matched controls completed a series of randomly applied multi-directional support surface translations. Whole-body metrics, e.g. peak center-of-mass displacement and net center-of-pressure displacement were compared across cohorts. Stability margin was computed as the difference between peak center-of-pressure and center-of-mass displacement. Additionally, center-of-pressure and ground reaction force magnitude and direction were compared between the prosthetic, intact, and control legs. Findings Peak center-of-mass displacement and stability margin did not differ between individuals with transtibial limb loss and controls for all perturbation directions except those loading only the prosthetic leg; in such cases the stability margin was actually larger than controls. Despite similar center-of-mass displacement, greater center-of-pressure displacement was observed in the intact leg during anterior-posterior perturbations, and under the prosthetic leg in medial-lateral perturbations. Further, in the prosthetic leg, ground reaction forces were smaller and spanned fewer directions. Interpretation Deficits in balance control among indivdiuals with transtibial limb loss may be due to their inability to use their prosthetic leg to generate forces that are equal in magnitude and direction to those of unimpaired adults. Targeting this force-generating deficit through technological or rehabilitation innovations may improve balance control.

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Introduction:The study presents the design and manufacturing of a custom silicone distal cup, with a high spatial resolution, to fit inside the prosthetic liner for the treatment of irregular morphology at the distal residual limb of a patient with lower-limb amputation. This distal cup for the inside of the prosthetic liner has intricate interior features matching the shape of the distal residual limb to prevent localized high-pressure regions. Methods: High-resolution 3D optical scanning, computer-aided design (CAD), and material extrusion (MEX) process for additive manufacturing of molds are three key techniques for designing and manufacturing this custom distal cup. A three-part mold for molding the distal cup with matching features was designed by CAD and fabricated by MEX. The subject evaluated the distal cup by walking using the distal cup before wearing the prosthetic liner in the lower-limb prosthesis. Results: A custom silicone distal cup was fabricated using a 3D-printed mold and evaluated using a Prosthetic User's Survey. Based on the survey, the insert has an acceptable comfort, suspension requirement, and ease of use. Conclusions: The scan by high spatial resolution Space Spider optical scanner could capture detailed features of the distal residual limb. The resulting distal cup had the protrusion that functioned to separate the invaginations. The subject was satisfied with the distal cup based on the Prosthetic User's Survey. Clinical Relevance: The approach to fabricate the custom silicone distal cup using a high-resolution 3D optical scanner and a 3D-printed mold can be applied to fabricate the distal cup with intricate features for a patient with irregular morphology at the distal residual limbs. (