An estimated 1.6 to 2 million amputees live in the United States, and each year another 185,000 people join those numbers. Only one in ten of those amputees use prostheses. Every amputation is unique, but uncomfortable prostheses or prostheses that are difficult to control sometimes make artificial limbs more difficult to wear than to abandon altogether.
But the medical, technological, and robotic communities are changing how they think about and approach amputations and prostheses. Advances in technology, from the amputation surgery itself to the technologies used to attach the prostheses to the body, have led to prostheses that feel and function more like a natural limb. They give amputees the ability to “feel” their limb in relation to their body and the surrounding world for better, more natural movement and function.
Where is Technology Taking Prosthetics?
Rethinking the Amputation Surgery
Researchers at the MIT Biomechatronics Lab have altered how physicians think about traditional amputation surgery. A traditional amputation cuts straight through skin, muscle, bone, nerves, and soft tissues, changing the relationships between muscle groups and leaving behind raw nerves.
New amputation methods include preserving nerves for placement in muscle grafts or artificial sensory devices to create or preserve control over existing or artificially created muscle pairings. Muscle pairings are often key to movement and coordination. For example, when you contract your calf muscles, the shin muscles stretch in response. Conversely, when the shin muscles flex, the calf muscles relax and stretch.
Using the body’s existing nerves with muscle grafts or artificial sensory devices allows amputees to control prostheses through muscle control and nerve impulses. Nerve endings and grafts become the body’s way of communicating with electrical sensors in prostheses and controlling the prostheses’ movement. Even more valuable, the newly formed nerve/muscle pairs communicate with the brain, telling the wearer where the prostheses are in relation to the body and surrounding space.
Myoelectric prostheses use electrical signals from muscles and muscle groups to activate preprogrammed movements and functions in a prosthesis. This technology comes from decades of pattern recognition research that started in the 1960s. Prior to the new technology, electrodes were attached to the skin’s surface, but changes in body position, sweat, and poor skin condition could get in the way of the electrical signal, making it difficult to control the prostheses.
The technology has evolved so that tiny magnetic electrodes, called IMES, are implanted directly into the muscle. The electrodes transmit electrical signals to sensors in the prosthesis, which then interpret them into preprogrammed movements and functions. Through battery-powered movement, the prostheses mimic natural body movements.
Other designs also incorporate artificial skin to replace the traditional socket. This “skin” mirrors the characteristics of the very skin it covers. Sensors alter the artificial skin’s softness or stiffness based on the body’s movements so that the prostheses feel like an extension of the body. Artificial skin also adds the benefit of sending back sensory information to the brain. The amputee can then “feel” the prosthesis in relation to the rest of the body and environment.
IMES, the electrodes used with myoelectric prostheses, are an example of sensory implants. Other types of sensory implants are placed on or near peripheral nerves to restore the connection between the brain and body movement. Cuff electrodes are a type of sensory implant that’s wrapped around the nerve to restore more function.
The implantation methods are changing too. Most sensory implants require a surgical procedure. Some researchers are developing injection methods to reduce the costs and risks of sensory implants.
Osseointegration involves integrating a piece of titanium or other biocompatible material directly into the bone. After a healing period, the prosthesis attaches to the implant, which acts like natural bone. Some of these prostheses also include sensory technology that provides feedback to the brain, helping the user know where their limb is related to their body and environment.
Virtual Therapy and Training
Training and therapy are changing too. Virtual training allows amputees to learn how to use different types of prostheses before putting on the device. This type of virtual training reduces the time it takes to learn how to use the prosthesis.
Virtual methods are also being used to better customize the fit of prostheses. These programs “learn” how each individual amputee uses their remaining muscles and nerves through movement and sensory technology. That knowledge lets therapists and prosthetists help people better learn to adapt to their prosthesis as well as make changes to the prosthesis for a better fit.
Preparing for New Innovations
Technology is expanding the options available to amputees so that more people can have the movement and function they want. The best way to prepare for new innovations—take care of your body. Skin care, muscle strength, and muscle balance will all play a role in your ability to adapt to new technologies. Some technologies will be available sooner than others, but no matter when they’re available, your physical health will matter. Take care now, so when the time comes, you’re prepared for everything that the latest amputation and prosthetic technologies have to offer.