Prostheses today – from mechanics to myoelectric technology

Prostheses have been part of the orthotist trade since humans first lost a body part and needed to regain some function. Today, prosthesis technology ranges from simple mechanical solutions to advanced systems with sensors, microprocessors, and electric motors. Common to them all is that they must be fitted to the individual user by an orthotist who understands both the craftsmanship and the technology behind it.

§Mechanical prosthetics – still a solid foundation

En stor del af de proteser, der bruges i hverdagen, bygger stadig på ren mekanik: fjedre, hydrauliske stempler og led, der reagerer på brugerens egen bevægelse og vægtoverførsel. Den slags proteser er ofte robuste, enkle at vedligeholde og mindre afhængige af strøm og elektronik, hvilket gør dem til et solidt og pålideligt valg for mange brugere, ikke mindst i hverdagssituationer, hvor enkelhed vejer tungere end avancerede funktioner.

§Microprocessor-controlled knees

At the other end of the scale are microprocessor-controlled prosthetic knees, where a built-in computer continuously adjusts the knee's resistance. Manufacturers like Ottobock use sensors such as gyroscopes, accelerometers, force sensors, and angle gauges in the knee joint itself to read how the user is moving and adjust the hydraulic resistance accordingly. Some models have features that react if the user stumbles, while others are designed for step-over-step stair descent and to provide a more stable standing function.

§Myoelectric arm and hand prostheses

For arms and hands, myoelectric prostheses are available, in which electrodes on the skin surface register the weak electrical signals from the user's own muscle activity. A built-in microprocessor converts the signals into specific movement commands, so the prosthesis can, for example, switch between different grip patterns. The advantage is that the user has a high degree of control over the prosthesis through their own residual musculature, but it also demands that the electrodes are positioned correctly and that the signals are calibrated to the individual user.

§The orthotist's role

Regardless of how advanced the electronics are, a prosthesis stands or falls with how well the socket – the part that connects the residual limb to the rest of the prosthesis – fits. This work is still very much a craft: the orthotist takes measurements or scans the residual limb, moulds the socket and adjusts it continuously as the limb's shape changes. At the same time, the orthotist often works closely with the supplier's technicians to set up and maintain the actual electronics so the prosthesis continues to function correctly.

“A prosthesis is never better than the socket it sits in – regardless of how much electronics are inside.”

— Practice from the workshop