Novel self-contained robotic arm prothesis yields increased sensory acuity

1. A self-contained robotic arm was shown to enable bidirectional communication between a prosthetic hand and implanted electrodes in the nerves and muscles of the upper arm.

2. Daily use of the self-contained robotic arm was shown to increase sensory acuity and effectiveness in daily life activities.

Evidence Rating Level: 4 (Below Average)

Study Rundown: Conventional arm protheses function depends on native biceps and triceps muscles, while compressing the stump. More advanced prostheses for the upper arm require the patients to master a steep learning curve to properly operate the device. Furthermore, both types of devices are unable to provide sensory feedback. As such, this study evaluated a self-contained, neuromusculoskeletal prosthetic arm which included sensory feedback from the surface of a prosthetic hand. Four participants had electrodes implanted into the heads of their biceps and triceps followed by fitting the self-contained arm prosthesis around a previous osseointegrated implant. The researchers found that the self-contained robotic arm enabled intuitive and unsupervised daily activities over a period of several years.  This case series study was limited by the difficulty in creating a standardized neural interface that transports a sufficient amount of information to the nervous system. Another limitation of the study was the small number of patients receiving the intervention, which hinders the ability to determine the universal applicability of the self-contained robotic arm. Nonetheless, this study was strengthened by its ability to successfully report long-term electrode implantation which provide somatosensory feedback in the daily environment of the participant. For physicians, these findings highlighted an alternative intervention for patients wanting a prothesis after a transhumoral amputation.

Click to read the study in NEJM

Relevant Reading: An Osseointegrated Human-Machine Gateway for Long-Term Sensory Feedback and Motor Control of Artificial Limbs

In-Depth [case series]: This case series enrolled 4 participants in a single-enter study from Sweden. Inclusion criteria included: adult participants older than 18 years of age; a previous transhumoral amuptation; and had an existing osseointegrated implant. The exclusion criteria for the study included upper extremity amputations other than the transhumoral amputation. The participants underwent a nerve transfer for hand open and closing through remnant muscles at the stump. The ulnar nerve was transferred to the short head of the bicep, and the radial nerve was rerouted to the lateral head of the triceps. Electrodes were placed on the biceps and triceps muscles to detect signals from voluntary contractions and to obtain sensory feedback. Finally, four to six weeks after the surgery the self-contained robotic arm was fitted around the existing osseointegrated implant. Initially, the patients were able to perceive tactile sensations with a frequency increase or decrease of 50%. However, after one month of daily use, the patients refined their ability to perceive tactile sensations with a frequency change of 30%. The neuromusculoskeletal interface remained functional for three to seven years post-surgery. Three participants, prior to the intervention, experienced phantom limb pain. After the intervention, two participants had complete relief of the phantom limb pain. Finally, the participants were able to gain more independence in accomplishing their daily activities with the self-contained robotic arm. Participant 1 gained full-time employment and the prothesis allowed him to enjoy his favorite past times such as skiing and ice fishing. Participant 2 has been able to repair cars and compete in rally-car racing. Participant 3 has been able to orienteer and canoe. Taken together, the study concluded the self-contained robotic arm improved the ability of the participants to accomplish their daily activities by increased sensory acuity.

Image: PD

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