Biomechanic Aspects and Patient Needs Lead the Path to a Unique Wristjoint for Myoelectric Prosthesis

The wrist plays an important role for the function of the human hand. The wrist joint is a complicated anatomical unit, consisting of various bones, ligaments and muscles. The distal and proximal joints combined with the rotation of the forearm excite movements at various levels that bring the hand into different positions. Apart from the rotation, the newly developed wrist with low construction height for myoelectric prostheses allows for volar and dorsal flexion at various locking positions. Besides those typical functions which allow positioning of the hand, the joint must meet further technical requirements. Therefore the prosthetic wrist joint clearly differs from its natural model. The most important difference is the exchangeability of the terminal device. This flexion joint with its additional degrees of freedom in motion considerably enhances the radius of action and thus increases the practical value of the myoelectric system to the patient. INTRODUCTION The function of an arm prosthesis is primarily determined by the quality of the prosthetic hand. After all, the patient uses it to grasp objects and carry out different activities. To be able to grasp these objects the prosthetic hand must optimally be positioned. In the human hand these movements are mainly and often unconsciously carried out with the wrist joint. Even hand gestures are actively supported by the movements of the wrist joint. The patient, however, often has to integrate shoulder movements into the whole process of movement. To simplify the entire process of movement for the patient, a new flexion wrist unit for myoelectric prostheses has been developed.