Artificial Joint
A new artificial joint restores important wrist-like movements to forearm amputees. (Credit: Chalmers University of Technology)

A new artificial joint restores important wrist-like movements to forearm amputees, something that could dramatically improve their quality of life. The new artificial joint works instead with an osseointegrated implant system developed by the Sweden-based company, Integrum AB — one of the partners in this project.

An implant is placed into each of the two bones of the forearm — the ulnar and radius – and then a wrist-like artificial joint acts as an interface between these two implants and the prosthetic hand. Together, this allows for much more naturalistic movements, with intuitive natural control and sensory feedback.

For patients missing a hand, one of the biggest challenges to regaining a high level of function is the inability to rotate one’s wrist, or to ‘pronate’ and ‘supinate’. When you lay your hand flat on a table, palm down, it is fully pronated. Turn your wrist 180 degrees, so the hand is palm up, and it is fully supinated.

Most of us probably take it for granted, but this is an essential movement that we use every day. Consider using a door handle, a screwdriver, a knob on a cooker, or simply turning over a piece of paper. For those missing their hand, these are much more awkward and uncomfortable tasks, and current prosthetic technologies offer only limited relief to this problem.

Patients who have lost their hand and wrist often still preserve enough musculature to allow them to rotate the radius over the ulnar – the crucial movement in wrist rotation. A conventional socket prosthesis, which is attached to the body by compressing the stump, locks the bones in place, preventing any potential wrist rotation, and thus wastes this useful movement.