New research from the University of Birmingham and Imperial College London showed that strengthening hip muscles could be key to improving mobility in people with unilateral transtibial amputations.
The study showed that knee extensor muscles are particularly at risk of atrophy because of people’s natural inclination to protect the soft tissue around the amputation site, but that hip abductors could be strengthened to provide effective compensation for weaknesses in the knee extensors. They tested their hypothesis with people with amputations across three activities essential for independent living: walking, getting up out of a chair, and climbing stairs.
“Even with a prosthesis, there will be reduced mobility in the amputated limb. People will also use their sound limb more and try to protect the soft tissue at the amputation site. All these factors combine to reduce muscle volume in the amputated limb. In addition, putting additional load on the intact limb can lead to further problems like osteoarthritis,” said Ziyun Ding, PhD, University of Birmingham, who led the research. “It’s inevitable that people with an amputation will try to protect those soft tissue areas, but the hip abductor muscle, a major muscle in the leg, is not part of the stump knee interface. By strengthening this muscle, the leg will work better, without overloading the knee extensor muscle.”
The research team worked with eight military personnel who had had a lower-limb amputation after being injured in combat. Those taking part in the study were at least 12 months post-operation and had had their prosthesis for at least six months. The researchers took high-resolution MRI measurements to get an accurate picture of how the muscle volume in the amputated limb had changed and captured motion data from the three activities. In addition, researchers used computational modelling to understand the internal loading, such as muscle force and bone on bone contact, which cannot be measured using imaging techniques.
Through these techniques, the team was able to get a clear picture of the biomechanics involved in each activity, which led them to identify the hip abductor muscle as key to improving functional mobility by working to strengthen it via targeted exercise activities or electrical stimulation.
Further work will seek to increase the size of the cohort being studied and examine how factors such as age, and type and cause of amputation might affect muscle atrophy.
Editor’s note: This story was adapted from materials provided by the University of Birmingham.