A new type of surgery that links muscles together may improve the precision of prosthetic use and also relieve pain.
In typical amputations, the muscle pairs (such as triceps and biceps) that work together to control the joints are severed. However, an MIT team has discovered that reconnecting these muscles that are in an agonistic-antagonistic (‘push-pull’) relationship improves the sensory feedback and thus precision of the affected limb.
“When one muscle contracts, the other one doesn’t have its antagonist activity, so the brain gets confusing signals,” explained Srinivasan, a former member of the Biomechatronics group now working at MIT’s Koch Institute for Integrative Cancer Research. “Even with state-of-the-art prostheses, people are constantly visually following the prosthesis to try to calibrate their brains to where the device is moving.”
The 15 patients who received the AMI surgery were able to flex their prosthetic ankle joint with more precision than those without it, who were only able to fully extend or flex their joint.
“Through surgical and regenerative techniques that restore natural agonist-antagonist muscle movements, our study shows that persons with an AMI amputation experience a greater phantom joint range of motion, a reduced level of pain, and an increased fidelity of prosthetic limb controllability,” says Hugh Herr, a professor of media arts and sciences, head of the Biomechatronics group in the Media Lab, and the senior author of the paper.
The surgery also had a completely unexpected benefit: the reduction of pain in the amputated area, which can be from neuromas or phantom limb pain. Phantom limb pain can occur in 80% of amputess. Six of the 15 AMI patients reported zero pain. This may be significant as in the five centuries since phantom limb pain was first described, there has not been much advancement in the understanding of it.
“Our study wasn’t specifically designed to achieve this, but it was a sentiment our subjects expressed over and over again. They had a much greater sensation of what their foot actually felt like and how it was moving in space,” Srinivasan says. “It became increasingly apparent that restoring the muscles to their normal physiology had benefits not only for prosthetic control, but also for their day-to-day mental well-being.”
To treat patients who had received the traditional amputation surgery, the team is also working on using muscle grafts to create a ‘regenerative AMI’ procedure that restores the effect of agonist and antagonist muscles.
Source: Medical Xpress
Journal information: Shriya S. Srinivasan el al., “Neural interfacing architecture enables enhanced motor control and residual limb functionality postamputation,” PNAS (2021). www.pnas.org/cgi/doi/10.1073/pnas.2019555118
