Compliant Prosthetic Wrists Entail More Natural Use Than Stiff Wrists During Reaching, Not (Necessarily) During Manipulation

Abstract

Developing an artificial arm with functions equivalent to those of the human arm is one of the challenging goals of bioengineering. State-of-the-artprostheses lack several degrees of freedom and force the individuals to compensate for them by means of compensatory movements, which often result in residual limb pain and overuse syndromes. Passive wristsmay reduce such compensatory actions, nonethelessto date their actual efficacy, associated to conventional myoelectric hands is a matter of debate. We hypothesized that a transradial prosthesiswould allow a simpler operation if its wrist behaved compliant during the reaching and grasping phase, and stiff during the holding andmanipulation phase. To assess this, we compared a stiff and a compliant wrist and evaluating the extent of compensatory movements in the trunk and shoulder, with unimpaired subjects wearing orthoses, while performing nine activities of daily living taken from the southampton hand assessment procedure. Our findings show indeed that the optimal compliance for a prosthetic wrist is specific to the phase of the motor task: the compliant wrist outperforms the stiff wrist during the reaching phase, whereas the stiff wrist exhibits more natural movements during the manipulation phase of heavy objects. Hence, this paper invites rehabilitation engineers to develop wrists with switchable compliance.

Grip control and motor coordination with implanted and surface electrodes while grasping with an osseointegrated prosthetic hand

“…The last decade has witnessed significant progress in the field of upper limb prosthetics. A deeper understanding of basic scientific questions in neurophysiology and neuroscience met novel surgical techniques and prosthetic components, such as articulated hands and myo-controllers that reached the market [1]. However, although myoelectric prostheses have increased dexterity and anthropomorphism, the control interface, namely surface electromyography (sEMG), has remained basically unchanged in the last four decades [2–4].…”

A 2-Degree-of-Freedom Quasi-Passive Prosthetic Wrist With Two Levels of Compliance

“…Taken collectively, the experimental comparisons between stiff and compliant wrists conducted so far, seem to point towards the same direction [12], [27], [28]. They suggest that a compliant wrist outperforms a stiff one during the reaching phase, as it yields to lower compensatory movements, whereas stiff wrists exhibit more natural movements during the manipulation phase of heavy objects.…”

“…With the same goal in mind, wrists with passive FE and/or RUD were also developed and made commercially available. These devices can be distinguished between stiff or compliant wrists [20], [27]. Stiff wrists enable the user to manually orientate and lock the hand in a desired and firm posture, while compliant ones, can be either locked in a certain posture or unlocked, to exhibit an elastic behavior.…”

Reachy, a 3D-Printed Human-Like Robotic Arm as a Testbed for Human-Robot Control Strategies

“…Regarding the end-effector, in respect to grasping with an arm prosthesis, a fixed wrist often requires the patient to perform extra shoulder and elbow movements to compensate for the lack of distal mobility. Thus, enabling wrist motion proves to be quite useful for a patient (Kanitz et al, 2018), as it enables a more natural and comfortable use. In this way, Reachy's 2-DoF wrist makes it suitable to address this aspect of prosthesis control.…”