Exercises of hip muscle boost mobility in people with below-the-knee amputation: Study

UK: A recent study has suggested that strengthening the hip and adductor muscles could improve functional mobility in patients with a below-the-knee amputation. The study appeared online in the Journal of Biomechanics in its March 2023 issue.

The researchers at the University of Birmingham and Imperial College London identified muscles around the hips, called hip abductors, which could be strengthened to compensate effectively for weaknesses in the knee extensor muscles. They tested their hypothesis in amputees across three activities essential for independent living: walking, getting up from a chair, and climbing stairs.

Amputation presents significant mobility challenges to millions of people worldwide. Studies show that only 5 per cent of people fitted with a prosthetic limb use it for more than half of their waking hours. These lower activity levels lead to muscle wasting, or atrophy, in the remaining leg part.

The study has shown that the knee extensor muscles, just above the knee, are particularly at risk of atrophy because of the natural inclination to protect the soft tissue around the amputation site.

Dr Ziyun Ding, of the University of Birmingham led the research. She said: “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.

“People with an amputation will inevitably 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. The leg will work better by strengthening this muscle without overloading the knee extensor muscle.”

In the study, the team worked with eight military personnel with lower limb amputations after being injured in combat. Those participating in the study were at least 12 months post-operation and had prostheses for at least six months.

The researchers took high-resolution MRI measurements to understand how the muscle volume in the amputated limb had changed. They also captured motion data from the three activities. In addition, researchers used computational modelling to understand internal loadings, such as muscle force and bone-on-bone contact, which cannot be measured using imaging techniques.

Through these techniques, the team could get a clear picture of the biomechanics involved in each activity. This led them to identify the hip abductor muscle as key to improving functional mobility by working to strengthen it post-amputation. This could be via targeted exercise activities or electrical stimulation, using techniques similar to those already employed for stroke patients.

Reference:

Ziyun Ding, David P. Henson, Biranavan Sivapuratharasu, Alison H. McGregor, Anthony M.J. Bull, The effect of muscle atrophy in people with unilateral transtibial amputation for three activities: Gait alone does not tell the whole story, Journal of Biomechanics, https://doi.org/10.1016/j.jbiomech.2023.111484.