Background insights

Disability statistics suggest that one billion people (around 15% of the world’s population) are living with a physical disability and around 190 million adults have a major functional difficulty. In contrast, the number of amputees and individuals born without limbs who gain access to prosthetics to restore mobility is very small.

​Spinal cord injury, paralysis and limb loss are the most visible and debilitating outcomes of road accident trauma – impacting thousands of people every day.

At Bionics Gamechangers, we look for all levels and types of innovation that enable limb, muscle and spinal mobility: prosthetic limbs that smoothly integrate with a person’s neuromuscular system and brain to enable movements (flexing, bending, improved gait), improved hand movement (grasping, rotating, fine motor control), e-suits and e-stimulation to assist with standing and walking.

Research is advancing, but consumer access is still very limited. The global call for more affordable, accessible, reliable and lighter bionic limbs and mobility devices is growing – and it’s getting louder.

Myoelectric limbs are the next step for many amputees. In this situation, a battery and electronic system (functional electric stimulation) is used to create muscle and nerve movement in the residual limb. For example, a prosthetic hand is controlled by muscle signals that enable wrist flexors and extensors to close and open the hand. Nowadays myoelectric hands enable a person to move each finger individually in response to signals from electrodes placed over muscles in the upper arm. If muscle signals can’t be used to control the prosthesis, then different types of switches are used. A greater number of tasks are possible with the use of sensors and motorised controls.

Prosthetics that use myoelectric sensors are the go-to solution for many with upper limb difference. However, the user’s level of control is very reliant on the fit between the stump and the prosthetic. The sensors must sit on the right areas of skin.

In some cases, procedures may be undertaken to reconnect nerves (those that would normally be connected to arm muscles) to the pectoralis muscles. As the individual thinks about moving their arm or hand, they flex the pectoralis muscles and this movement is picked up by external electrodes that send a message to the prosthetic that the person is wearing. Similar techniques of targeted muscle re-innervation (TMR) are used to control the movement of leg prostheses. However, myoelectric sensors tend to work better in hands and arms than in legs because the movement of knees, feet and ankles is more autonomous and less consciously undertaken.

Current research is focused on either improving (1) the design of prosthetic limbs and socket technology or, (2) the design of osseointegrated prosthetic systems that join the prosthesis to bone.

Limb and socket designs are areas in focus for continued improvement. After an early consultation and a long wait, the stump has sometimes changed in shape or size due to weight gain and even the best-designed sockets can slip and cause discomfort and pain (especially on lower limbs).

There is growing interest in osseointegration or bone anchored prostheses. For transfemoral amputees (amputations that pass through the femoral artery), research has shown that bone-anchored prostheses deliver the best hip and pelvic motion when a person is walking, better perceptions of vibration, improved comfort while sitting, and better overall functionality. However, post-operative infections and phantom pain in the vicinity of missing limbs are key issues yet to be resolved. Stress is also felt where the osseointegrated prosthetic implant interfaces with residual bone.

Researchers are focused on any potential failures in the osseointegration that might come about due to stress in the vicinity of the bone integration. Understanding whether this stress increases or reduces when different prosthetic designs are used is a priority. Research is also ongoing to identify ways to resolve phantom pain. There is some evidence that neural sensory feedback – sensations of knee motion and the sole of the foot touching the ground – can decrease fatigue, increase walking speed and also reduce the phantom limb pain.

Delivery of genuine bionic mobility is no doubt the most desired outcome – a prosthetic limb that smoothly integrates with the person’s neuromuscular system and brain to enable movements such as flexing, bending and grasping.

Bionic mobility is achieved through the interaction of thought, action and response. For sustained movements (bionic mobility), microelectrodes are implanted in specific areas of the motor cortex to give the strong signals needed to control bionic limbs. A new electronic pathway connects the mechatronic limb with the brain and peripheral nerves are bypassed. Research in the field of bionic mobility is advancing across different continents, but consumer access to thought-controlled mobility trials and related technologies is still limited.

Exoskeletons and e-suits used in rehabilitation of spinal cord injury patients and e-suits that assist with everyday movement are a growing area of bionic innovations. Society’s shift to increased inclusivity, de-stigmatisation and acceptance of disability augurs well for further take-up of these wearable devices. Our ageing population, an increasing number of spinal cord injury patients plus people whose individual mobility is impacted by stroke, cerebral palsy and chronic diseases (such as multiple sclerosis and Parkinson’s disease) are growing markets for exoskeletons in the decade ahead.

The strengths of functional electric stimulation (FES) in assisting with recovery in chronic stages of spinal cord injuries are also gaining increased attention. Together, FES and a new generation of implanted spinal stimulators for pain management play a vital role in today’s bionic rehabilitation therapies for spinal cord injury. New additions to implanted stimulators in 2022 include the Australian-born Evoke Spinal Cord System and the Senza Spinal Cord Stimulation (SCS) system recently approved to treat chronic pain.

In recent years, FES has also been applied to a greater extent to assist SCI patients with bladder and bowel functions. In this regard, there is a growing body of knowledge about the effect and likely utility of spinal cord stimulation to treat neurogenic bladder after spinal cord injury, but more work is still to be done on stimulation mapping and treatment protocols.