A limb amputation - removal of a body extremity by surgery of trauma, is associated with functional impairment, disability, and a poor health-related quality of life. Prostheses were designed to improve function and self-image to provide the patients with a sense of wholeness.
New-generation prostheses providing somatosensory feedback are more functional than conventional types of prostheses.
New-generation prostheses have also been shown to improve mobility, embodiment, and post-amputation pain.
Recent surgical techniques (e.g., RPNI) can enhance the functionality of a prosthesis.
Nevertheless, early prosthetic limbs were heavy, could not mimic the functional movements of the amputated limb, and could not easily be controlled by an individual wearing them.
Recent and more innovative prostheses have sought to address the shortcomings of previous prosthetic designs. In this article, we discuss the three types of new-generation prostheses that are available in the market. In addition, we discuss the strengths and limitations of each prosthesis type. Finally, we provide recommendations on where one could get these prostheses.
An externally controlled myoelectric prosthesis
An externally controlled myoelectric prosthesis is a robotic limb that moves via electric signals generated by the contraction and relaxation of the residual limb muscles. This type of prosthesis gets connected to two muscle groups (flexors and extensors) of the residual limb via small electrical wires and electrodes.
The electrical signals generated by these muscles are then paired with a computer algorithm that generates corresponding prosthetic limb movements. For example, the signals generated by relaxing and contracting the forearm muscles cause the prosthetic hand to close and open, respectively. This allows the patient to perform functional tasks such as holding a cup to drink water by activating the residual limb muscles only (Figure 1). This prosthesis type has many benefits over cosmetic prostheses in that patients can perform functional tasks.
In addition, it is comfortable and relatively easy to operate. The downside of this prosthesis type is that it is expensive, heavy, and not useful for performing fine and complex movements. Furthermore, it lacks somatosensory feedback essential for smooth limb movement and embodiment.
A prosthesis with somatosensory feedback
A prosthesis with somatosensory feedback is an assistive device that enables the patient to walk and feel their leg during movement. For patients with above-knee amputations, the prosthesis is equipped with sensors under the sole and around the ankle joint to detect movement in these areas whenever the foot touches and leaves the ground.
The movement signals from the foot and ankle sensors are then transferred (via Bluetooth) to the surgically implanted electrodes, which then stimulate the peripheral nerve innervating the amputated foot. Stimulating the peripheral nerve results in a perception of normal movement-related sensations in the phantom foot.
For instance, when the patient steps on a soft object with a prosthesis, the sensors relay signals associated with this stimulus to the peripheral nerve, which will then generate the sensation of stepping on a soft object in the phantom foot. Several studies have shown that using a prosthesis with somatosensory feedback improves function, embodiment, and phantom limb pain.
A prosthesis using a regenerative peripheral nerve interface
Regenerative Peripheral Nerve Interface (RPNI) is a surgical technique primarily designed for improving prosthesis control, although recently, it is also used as a strategy for preventing or treating neuroma-related pain in amputees. Regenerative peripheral nerve interface involves cutting off the neuroma at the end of the peripheral nerve, dissecting the nerve to expose nerve fascicles, and then wrapping each fascicle with a muscle graft harvested from a healthy donor site (Figure 2). Over the following three months, the focus is on improving the muscle grafts’ blood supply and reinnervation by the peripheral nerve fascicles.
Ultrasounds have shown strong muscle graft contractions during movements of the phantom limb. Signals from these contractions are used for controlling the prosthetic limb that is fitted to the residual limb (with RPNI) and connected via electrodes. This differs from externally controlled myoelectric prostheses in that the prosthetic limb expresses the movement intention generated by the brain. For example, if the person consciously generates a movement intention of holding a cup, the prosthetic hand will hold a cup in real time. Better control and function are among the many benefits of using a prosthesis controlled by RPNI.
Early prosthetic limbs were used primarily for cosmetic purposes. However, the need for functional prosthetic limbs grew over time, and the incorporation of technology provided a solution to some of the pressing problems involved in designing and using prosthetic limbs. Current technological inventions and surgical techniques aim to improve the functional level of prostheses to that of a healthy human limb. These new-generation prostheses have been shown to improve mobility, embodiment, function, and pain.