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BackgroundCurrent upper limb prostheses do not replace the active degrees-of-freedom distal to the elbow inherent to intact physiology. Limited evidence suggests that transradial prosthesis users demonstrate shoulder and trunk movements to compensate for these missing volitional degrees-of-freedom. The purpose of this study was to enhance understanding of the effects of prosthesis use on motor performance by comparing the movement quality of upper body kinematics between transradial prosthesis users and able-bodied controls when executing goal-oriented tasks that reflect activities of daily living.MethodsUpper body kinematics were collected on six able-bodied controls and seven myoelectric transradial prosthesis users during execution of goal-oriented tasks. Range-of-motion, absolute kinematic variability (standard deviation), and kinematic repeatability (adjusted coefficient-of-multiple-determination) were quantified for trunk motion in three planes, shoulder flexion/extension, shoulder ab/adduction, and elbow flexion/extension across five trials per task. Linear mixed models analysis assessed between-group differences and correlation analysis evaluated association between prosthesis experience and kinematic repeatability.ResultsAcross tasks, prosthesis users demonstrated increased trunk motion in all three planes and shoulder abduction compared to controls (p ≤ 0.004). Absolute kinematic variability was greater for prosthesis users for all degrees-of-freedom irrespective of task, but was significant only for degrees-of-freedom that demonstrated increased range-of-motion (p ≤ 0.003). For degrees-of-freedom that did not display increased absolute variability for prosthesis users, able-bodied kinematics were characterized by significantly greater repeatability (p ≤ 0.015). Prosthesis experience had a strong positive relationship with average kinematic repeatability (r = 0.790, p = 0.034).ConclusionsThe use of shoulder and trunk movements by prosthesis users as compensatory motions to execute goal-oriented tasks demonstrates the flexibility and adaptability of the motor system. Increased variability in movement suggests that prosthesis users do not converge on a defined motor strategy to the same degree as able-bodied individuals. Kinematic repeatability may increase with prosthesis experience, or encourage continued device use, and future work is warranted to explore these relationships. As compensatory dynamics may be necessary to improve functionality of transradial prostheses, users may benefit from dedicated training that encourages optimization of these dynamics to facilitate execution of daily living activity, and fosters adaptable but reliable motor strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/1743-0003-11-132) contains supplementary material, which is available to authorized users.

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III.

Shoes altered prosthesis mechanical characteristics in the sagittal and frontal planes, suggesting that shoe type should be controlled or reported in research comparing prostheses. Understanding of how different shoes could alter certain gait-related characteristics of prostheses may aid decisions on footwear made by clinicians and prosthesis users. Clinical relevance Shoes can alter function of the prosthetic foot-shoe system in unexpected and sometimes undesirable ways, often causing similar behavior across setups despite differences in foot design, and prescribing clinicians should carefully consider these effects on prosthesis performance.

BackgroundProsthetic feet are spring-like, and their stiffness critically affects the wearer’s stability, comfort, and energetic cost of walking. Despite the importance of stiffness in ambulation, the prescription process often entails testing a limited number of prostheses, which may result in patients receiving a foot with suboptimal mechanics. To understand the resolution with which prostheses should be individually optimized, we sought to characterize below-knee prosthesis users’ psychophysical sensitivity to prosthesis stiffness.MethodsWe used a novel variable-stiffness ankle prosthesis to measure the repeatability of user-selected preferred stiffness, and implemented a psychophysical experiment to characterize the just noticeable difference of stiffness during locomotion.ResultsAll eight subjects with below-knee amputation exhibited high repeatability in selecting their Preferred Stiffness (mean coefficient of variation: 14.2 ± 1.7%) and were able to correctly identify a 7.7 ± 1.3% change in ankle stiffness (with 75% accuracy).ConclusionsThis high sensitivity suggests prosthetic foot stiffness should be tuned with a high degree of precision on an individual basis. These results also highlight the need for a pairing of new robotic prescription tools and mechanical characterizations of prosthetic feet.

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Bilateral transtibial amputee (BTA) gait has been investigated less and is not as well understood compared to that of their unilateral counterparts. Relative to able-bodied individuals, BTAs walk with reduced self-selected speeds, increased step width, hip-hiking, and greater metabolic cost. The clinically observed upper body motions of these individuals have not been quantified, but appear substantially different from able-bodied ambulators and may impact upright balance. Therefore, the objective of this study was to characterize the upper extremity kinematics of BTAs during steady-state walking. We measured medial-lateral ground reaction forces, step width and extrapolated center-of-mass (XCoM) trajectory, and observed effects of walking speed and increased prosthetic ankle range-of-motion (ROM) on these parameters. Significantly, BTAs display greater lateral trunk flexion ROM and shoulder abduction than able-bodied individuals when walking at similar speeds, and the inclusion of prosthetic adaptors for increasing passive ankle ROM slightly reduced step width. Overall, exaggerated lateral trunk flexion ROM was invariant with step width. Results suggest that lateral trunk motion is useful for shifting the body center-of-mass laterally onto the leading stance limb while simultaneously unloading the trailing limb. However, exaggerated lateral trunk flexion may introduce an unstable scenario if the XCoM is displaced beyond the lateral base-of-support. Further studies would be useful to identify if either prostheses that assist limb advancement and/or gait training may be effective in reducing this lateral sway while still maintaining efficient ambulation.