Game-Changing Sensory Neuroprosthesis Helps Amputees Recover from Falls
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More than half of people with lower limb loss say they are scared of falling, which makes them avoid some daily activities. This fear often comes from a lack of plantar sensation or the inability to feel sensations or pressure on the bottom of their prosthetic feet, which is important for keeping balance and walking properly. One way to address this issue is by giving prosthetic users sensory feedback through nerve stimulation. A study published in the international science research journal Nature in January 2025 showed that this approach could be effective.
The Importance of Plantar Sensation
The ability to feel sensations in the soles of our feet is vital for maintaining balance. This feeling helps our bodies understand how our feet are positioned on the ground, allowing us to make the necessary movements to stay stable. Research has shown that this sensitivity in the feet plays a crucial role in helping people recover from falls, especially for older adults.
To help prevent falls, some products, like raised-edge insoles, have been created to improve how individuals feel the pressure and weight on their feet. Additionally, training programs designed to enhance sensitivity in older adults have been shown to increase both their stability and confidence when recovering from a fall.
However, people who have lost a leg and use prostheses no longer experience the same sensation in their feet. They mainly rely on limited feedback from their residual limb interacting with the prosthetic socket.
Studies have indicated that when people with lower limb loss fall, their recovery strategies differ from those of people without physical disabilities. They tend to quickly try to get their intact foot back on the ground, showing a preference for their biological limb as it provides better sensory information. Yet, this change in strategy can lead to instability, making it more difficult to stay upright. Sometimes, it can cause them to hop or skip, lifting both feet off the ground at once, which adds to the challenge of maintaining balance.
People who have lost a leg and use prostheses no longer have plantar sensation. They mainly rely on limited feedback from their residual limb interacting with the prosthetic socket, making it difficult to recover from falls.
Currently, efforts to prevent falls among individuals with lower limb amputations often focus on enhancing strength and balance, which can boost confidence and mobility. Furthermore, there are some techniques that safely reduce impact when falling to prevent injuries. However, these methods require a lot of time and effort and don’t specifically address the balance issues caused by the lack of sensation in the feet.
The Sensory Neuroprosthesis
To address the issue, the researchers created a device called a ‘sensory neuroprosthesis.’ It's designed to help people who have lost their lower limbs to feel sensations in their prosthetic feet. This device uses special electrodes placed around the nerves in the residual limb, just above the knee.
By sending small electric currents to these nerves, the device can produce sensations that mimic how it would feel to have biological feet, especially when pressure is applied to the prosthesis.
The study
The study examined three participants with different types of leg amputations—two with below-knee amputations and one with above-knee amputations. They shared some interesting experiences while using a sensory neuroprosthesis.
When they applied pressure to specific areas of their prosthetic feet, like the heel and midfoot, they reported feeling comfortable sensations similar to what they felt in their sound side foot. This feedback suggests that the sensory neuroprosthesis effectively restores some sensory experience.
The researchers also explored how the device could help with stumble recovery—an important skill for preventing falls. The researchers conducted the experiments on a treadmill while the participants wore the neuroprosthesis. They introduced sudden changes in speed to simulate tripping.
Results
The results showed that with the sensory neuroprosthesis, the participants had better control of their trunks and improved stability when recovering from stumbling. They displayed more coordinated movements and reduced sideways trunk rotation, which indicates they felt more confident using their prosthetic limbs.
The researchers found that the sensory neuroprosthesis encouraged users to rely on their prosthetic foot more than on their intact foot. This shift was reflected in the increased peak Ground Reaction Forces under the prosthetic foot (the prosthetic foot was hitting the ground harder), suggesting improved confidence and stability. Even when the prosthetic foot was in the air, the participants showed better overall body control.
The researchers found that the sensory neuroprosthesis encouraged users to rely on their prosthetic foot more than on their intact foot.
Although the sensory neuroprosthesis helped the study participants feel more secure and less anxious about their ability to recover from stumbling, the researchers noted differences in their responses, likely due to how each person adapted to the disturbances on the treadmill. Furthermore, psychological factors, such as fear of falling, can affect how someone recovers from stumbling.
The bottom line
Overall, the research highlights the potential of sensory neuroprosthesis technology in enhancing stability, reducing the risk of falls, and improving confidence for individuals with lower limb loss. By restoring sensations on the prosthetic foot, the device helps users feel more connected to their prostheses, leading to better motor planning and smoother recoveries when tripping.
