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Biomechanics

Biomechanics - Poster Session B

Poster E6 - Evaluation of an Upper Limb Prosthesis Simulator with Varying Wrist Positions

Thursday, October 24, 2024
2:45 PM - 3:45 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Prosthetic simulators allow non-amputees to utilize prosthetic components and are vital in evaluating the functionality of prosthetic devices and enhancing their design. This study aims to evaluate the functionality of a body-powered upper-limb prosthetic simulator by developing a testing protocol that examines the categories of prehension, aiming, and turning/rotating. These categories test manual dexterity and include activities of daily living (ADL) that users of upper-limb prosthetic devices may perform. In addition, the study also analyzes the significance of utilizing a prosthetic wrist unit in performing these activities of daily living and manipulation tasks. Many high dexterity prosthetic hands are commercially available for prosthetic users, but this study focuses on assessing a wrist unit that manually reorients the position of a terminal device, to determine if there is a relevance in performing manipulation tasks with the varying angles in the wrist unit. The angles tested will be nearly 70% of the maximum anatomical range of motion in the wrist during (Nelson David L. and Mitchell, 1994).

Materials and

Methods:  The development of the prosthetic simulator used a four-bar mechanism as its base. This allowed for the motion of the terminal device to be parallel to the user’s forearm and eliminated the ability to pronate and supinate the device. The simulator’s use resembled a trans-radial amputee as pronation and supination are typically not possible.

To incorporate varying wrist positions during the tests, a two degrees of freedom locking joint was designed. The wrist unit locks in specific angles to ensure stability while performing tasks. The neutral position was envisioned with arm pronated, the thumb is in a medial direction such that for flexion the joint will bend downwards, extension upwards, radial inwards, and ulnar outwards.

All study procedures were reviewed and approved by the Institution Review Board (IRB). Prior to participating, written informed consent was obtained. Participants performed the modified Box and Blocks Test (BBT), modified Nine Hole Peg Test (NHPT), turned a steering wheel, rotated a lever door handle, and turned a key in a deadbolt door lock. The total time to complete the tasks, with a maximum of 120 seconds per task, and a comfort level for each wrist condition was recorded. Each participant completed the tasks with no simulator, with the simulator wrist in a neutral position, flexed position (50 degrees), extended position (50 degrees), radial deviation (15 degrees), and ulnar deviation (25 degrees). The order of the wrist positions was randomized, and the participant completed all tasks and positions with both dominant and non-dominant arms.

Results, Conclusions, and Discussions: During the test trials, participants used compensatory body movements to power the simulator and perform the manipulation tasks. The operating shoulder was frequently raised and lowered, leading to slight fatigue and discomfort. Participants were allowed to move the simulator in any way such that they were able to successfully complete the task, leading to the continuous raising and lowering of the shoulder and frequent bending and rotating of the torso. For certain wrist angles (ulnar and radial deviation and flexion), compensatory body movements were minimized, and participants rated a level 3 or 4 for comfortability indicating a higher level of comfortableness while performing the tasks with the simulator. Table 2 shows that ulnar deviation and wrist flexion had the highest average comfort score. These angles were optimal for completing some tasks given it required less raising of the shoulder to operate the simulator and therefore less fatigue/overexertion of other body movements in the shoulder, elbow, torso etc. Moreover, including the varying wrist angles lead to greater manipulation capabilities/dexterity in some of the tasks.

While performing tasks most participants found it difficult to see what the terminal device was picking up. This resulted from their line of sight being blocked by the sliding handle on the four-bar mechanism. Some participants found the length of the sliding handle was too short and the distance from the bike brake to the sliding handle was too far for smaller hands. One participant opted out of completing the trials due to discomfort in holding the handle with the printed, thin filaments protruding and scraping the palm. Both design dimensions and print quality of the handle led to discomfort in most participants while operating the simulator. In the future comfort should be taken into consideration with the design of the sliding handle and placement of the terminal device for clearer sight. In addition, by including optimal angles of operation/those used frequently in activities of daily living (such as wrist flexion), this study contributes to the design of static wrist prosthetics and the general knowledge of the relevance in high dexterity prosthetic wrists.

Acknowledgements (Optional):