Comparison of range-of-motion and variability in upper body movements between transradial prosthesis users and able-bodied controls when executing goal-oriented tasks.

BACKGROUND: Current 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. METHODS: Upper 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. RESULTS: Across 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). CONCLUSIONS: The 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.

Assessing the prosthetic needs of farmers and ranchers with amputations.

PURPOSE: Farmers and ranchers experience disabling injuries each year of which amputations account for 11%. Anecdotal evidence suggests that current prostheses may not be meeting the needs of farmers and ranchers with amputations. To better understand those prosthetic needs, a descriptive qualitative study was used to gather data with an engineering perspective. METHOD: Farmers with an upper- or lower-limb amputation were interviewed. Issues explored included current and past prostheses used, prosthetic failures, and ability to complete farm tasks using a prosthesis. Prosthetists providing services to this population were also interviewed to gain knowledge of specific devices and practises used in their geographic region. RESULTS: Interviews with 40 farmers and 26 prosthetists revealed several common themes related to prostheses including durability/utility, environment, adaptation, cost, and education. Farmers and ranchers with amputations often made modifications to their prostheses, farm equipment, and daily routines in order to return to their vocation. CONCLUSIONS: Farmers and ranchers with amputations have distinct prosthetic needs. Their return to farming can be facilitated by creating more durable, affordable, and adaptable prosthetic components. Our results can help guide design of more comprehensive surveys for further information gathering and new devices and establish best prosthetic practises for farmers and those in other physically demanding professions.

The effects of static friction and backlash on extended physiological proprioception control of a powered prosthesis.

In general, externally powered prostheses do not provide proprioceptive feedback and thus require the user to rely on cognitively expensive visual feedback to effectively control the prosthesis. Applying the concept of extended physiological proprioception (EPP) to externally powered prostheses provides direct feedback to the user's proprioceptive system regarding the position, velocity, and forces applied to the prosthesis. However, electric elbows with EPP controllers developed at the Northwestern University Prosthetics Research Laboratory have exhibited unexplained "jerky" behavior in both clinical fittings and bench-top operation. In addition, the development of limit cycles, a specific type of constant-amplitude oscillation, had been observed in bench-top use of these elbows. Backlash and static friction within the EPP system were found to be primarily responsible for the development of limit cycles. Reducing static friction and backlash improved the system's performance. These results suggest that to most effectively implement EPP, prosthesis manufacturers should design prosthetic components that minimize static friction and backlash.