New surgery may enable better control of prosthetic limbs – study

Nina Massey, PA Science Correspondent
·3-min read

Researchers have invented a new type of amputation surgery that can help amputees better control their residual muscles and sense where their “phantom” limb is in space, a new study suggests.

This restored sense should translate to better control of prosthetic limbs, as well as a reduction of limb pain, the researchers say.

In most amputations, muscle pairs that control the affected joints, such as elbows or ankles, are severed.

But researchers at the Massachusetts Institute of Technology (MIT) have found that reconnecting these muscle pairs, allowing them to retain their normal push-pull relationship, offers people much better sensory feedback.

Shriya Srinivasan, lead author of the study, said: “Both our study and previous studies show that the better patients can dynamically move their muscles, the more control they’re going to have.

“The better a person can actuate muscles that move their phantom ankle, for example, the better they’re actually able to use their prostheses.”

In the study, published in Proceedings of the National Academy of Sciences, 15 patients who received this new type of surgery, known as agonist-antagonist myoneural interface (AMI), could control their muscles more precisely than patients with traditional amputations.

The AMI patients also reported feeling more freedom of movement and less pain in their affected limb.

Hugh Herr, head of the biomechatronics group in the MIT Media Lab and the senior author of the paper, said: “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.”

In the new study, the researchers measured the precision of muscle movements in the ankle and a foot joint of 15 patients who had AMI amputations performed below the knee.

These patients had two sets of muscles reconnected during their amputation – the muscles that control the ankle, and those that control the subtalar joint, which allows the sole of the foot to tilt inward or outward.

The study compared these patients to seven people who had traditional amputations below the knee.

According to the study, the AMI patients’ ability to control these muscles was a lot more intuitive than those with typical amputations

This was largely to do with the way their brain was processing how the phantom limb was moving, the scientists said.

The researchers have also developed a modified version of the surgery that can be performed on people who have already had a traditional amputation.

This process, which they call regenerative AMI, involves grafting small muscle segments to serve as the agonist and antagonist muscles for an amputated joint.

They are also working on developing the AMI procedure for other types of amputations, including above the knee, and above and below the elbow.

Prof Herr said: “We’re learning that this technique of rewiring the limb, and using spare parts to reconstruct that limb, is working, and it’s applicable to various parts of the body.”