New surgical technique could improve control of prosthetic limbs after amputation

Researchers from MIT and Harvard Medical School have invented a new type of amputation surgery that could leave amputees with better control of residual muscles. The team believes improved control of those residual muscles could allow them to receive sensory feedback from prosthetic devices. Enhanced control of the residual muscles could enable amputees to sense where their "phantom limb" is in space.

The research team hopes the new surgical technique's benefit will be better control of prosthetic limbs and reduced limb pain. Typically, in an amputation, muscle pairs that control the affected joints like the elbow or ankles are severed. Researchers have found the reconnecting those muscle pairs allows them to retain their normal push-pull relationship providing better sensory feedback.

MIT researchers say their study and previous studies show that the better amputees can dynamically move muscles, the more control they will have. Essentially, with improved ability to actuate muscles that moved their phantom ankle, the better they're able to use a prosthetic device. Researchers on the project have used the new technique, known as the agonist-antagonist myoneural interface (AMI), with 15 patients.

Compared to patients who received traditional amputations, AMI patients can control the muscles more precisely and report more freedom of movement and less pain in the affected limb. Muscles that control the movement of the limb typically occur in pairs that alternatively stretch and contract. That stretching and contracting sends sensory information to the brain, and with conventional limb amputation, the muscle movements are restricted, eliminating that sensory feedback.

Without the sensory feedback, it's harder for amputees to feel where prosthetic limbs are in space or sense the force applied to the limb. With the new technique, instead of severing each muscle, the two ends of the muscle are connected, so they still dynamically communicate with each other within the residual limb. Since the preclinical studies, 25 people have undergone AMI surgery. Researchers have found that those who received AMI can control the muscles of the amputated limb more precisely than those who received traditional amputations.