Traditional limb amputation is often seen as a surgery of last resort. Tissue below the amputation site is discarded and muscles from the residual limb are secured to the bone. This process severs the connections between antagonistic muscle pairs that would otherwise contract and relax in synchronization, and it prevents muscles from communicating information back to the central nervous system. Traditional amputation can lead to painful phantom limb symptoms, muscle atrophy and, at a time when prosthetic technology is advancing at a rapid pace, limit a patient’s options for prosthetics.
A clinical team from Brigham and Women’s Hospital and Brigham and Women’s Faulkner Hospital led by Matthew Carty, MD, in collaboration with Hugh Herr, PhD, and his team of biomechatronics experts at the MIT Media Lab Center for Extreme Bionics, have developed a new approach to broaden the possibilities for patients who receive amputation surgery. In a paper published online in PRS Global Open, Carty and colleagues present the Ewing Amputation, a new surgical procedure performed at Brigham and Women’s Faulkner Hospital. The authors include case descriptions from the first three patients, as well as clinical outcome measures that show that the surgical procedure can preserve dynamic agonist-antagonist muscle relationships.
“The Ewing Amputation is a first step toward redefining the notion of amputation from one of surgical failure to an alternative form of limb salvage,” said Carty. “It has the potential to limit phantom limb pain and muscle atrophy, while preserving the patient’s ability to control muscle activation. This case study demonstrates the potential of the Ewing Amputation to benefit people with a below-the-knee amputation, irrespective of their chosen prosthetic system.”
“One potential benefit of the Ewing Amputation is the reduction of residual limb atrophy in time,” said Herr. “Since the surgical procedure allows residual limb muscles to remain dynamic, the residuum is less prone to atrophy. By maintaining soft tissue mass and volume, a prosthesis can be fit to the residuum with a greater degree of comfort and health.”
The Ewing Amputation incorporates an agonist-antagonist myoneural interface (AMI), in which dynamic muscle relationships are preserved within the amputated limb. Made up of two muscle-tendons (agonist and antagonist) that are surgically connected to allow one muscle to contract while the other muscle stretches, the AMI allows an amputee to control and interpret feedback from their prosthesis, including speed, location and more, based on feedback from a bionic joint. The AMI’s ability to improve control and interface with limb prosthetics is described in a related study published recently in Science Translational Medicine. The current paper details the operative technique for AMI construction in patients.
“The Ewing Amputation has important implications for the control and embodiment of advanced prosthetic limbs," said Tyler Clites, Postdoctoral Associate at the MIT Center for Extreme Bionics and lead author on the study. “The discrete signals from each muscle facilitate natural neural control of the robotic device, and are typically compromised in the traditional amputation surgery.”
As reported in the paper, AMIs were constructed for three subjects to control and interpret sensory information from a bionic ankle and subtalar joints. Intraoperative, perioperative and postoperative residual-limb outcome measures were recorded and analyzed, including electromyographic and radiographic imaging of AMI musculature.
Patients included in the pilot study were:
• Patient 1: a 52-year-old male with no significant past medical history who sustained multiple injuries in the context of a 50-foot fall in 2014.
• Patient 2: a 25-year-old male Army veteran with no significant past medical history,
who sustained multiple injuries in the context of an IED explosion in 2013.
• Patient 3: a 36-year-old male with a congenital left clubfoot deformity, resulting in a
prolonged history of recurrent metatarsal fractures throughout childhood and adolescence.
All three patients reported a high degree of phantom limb position perception without phantom limb pain. They also demonstrated an ability to generate discrete neural commands associated with movement of their phantom joints. The team reports that the AMI appeared to preserve the natural relationships between antagonistic muscle pairs, avoiding the disruptions caused by traditional amputations when the coupling between opposing muscles is severed.
“We hypothesize that maintenance of these key muscle relationships is essential to avoiding aberrant phantom sensation and preventing the chronic neurological remapping that has been identified as a predominant cause of phantom pain,” said Carty.
The research team notes that they are reporting on a very small number of patients, and no statistical claims can be made about the relative benefits of the Ewing Amputation as compared to a traditional below-the-knee amputation. To address this limitation, a case-control, prospective clinical trial is currently underway.
To date, Carty’s team has performed 11 Ewing Amputations as well as one above-the-knee amputation.
Herr has a consulting relationship with Ottobock. Herr and Carty are inventors on an issued patent describing the AMI concept. Herr, Carty and co-authors are inventors on a pending patent describing the Ewing procedure. MIT holds both patents.
Paper cited: Clites, TR et al. “The Ewing Amputation: The First Human Implementation of the Agonist-Antagonist Myoneural Interface” Plastic and Reconstructive Surgery