A new type of amputation surgery could help amputees better control their prosthetic limbs, a study has found.
The research could have major implications for Armed Forces personnel who have had limbs amputated due to injuries sustained while serving.
Carried out at the Massachusetts Institute of Technology (MIT), the study saw 15 patients receive a new type of surgery, known as agonist-antagonist myoneural interface (AMI).
In most amputations, muscle pairs controlling the affected joints, such as elbows or ankles, are severed.
But researchers found that reconnecting these muscle pairs, allowing them to retain their normal push-pull relationship, offers people much better sensory feedback.
All 15 patients in the study could control their muscles more precisely than patients with traditional amputations, and 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 senior author of the paper, said the study shows AMI allows for "a greater phantom joint range of motion, a reduced level of pain, and an increased fidelity of prosthetic limb controllability".
In the study, the researchers measured the precision of muscle movements in the ankle and a foot joint of 15 patients who had AMI surgery performed below the knee.
The patients then had two sets of muscles reconnected during their amputation – those that control the ankle and the subtalar joint, which allows the sole of the foot to tilt.
The 15 amputees were compared to seven people who had traditional amputations below the knee and, 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 down to the way their brain was processing how the phantom limb was moving, the scientists said.
Shriya Srinivasan, lead author of the study, said "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," she said.
Researchers have also developed a modified version of the AMI surgery that can be performed on those who have already had a traditional amputation.
Called regenerative AMI, the process involves grafting small muscle segments to serve as the 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."
Cover image: PA.