A prosthesis or an orthosis such as a hand prosthesis (10) comprises a moveable component (12). The moveable component (12) has a motor (14) operable to drive a worm gear (16). The hand prosthesis (10) also comprises a worm gear wheel 18 fixedly mounted on a support member (20). The moveable component (12) extends generally tangentially with respect to the worm gear wheel (18) and is mounted for rotation about the worm gear wheel (18). The worm gear (16) is in engagement with the worm gear wheel (18) such that, when the motor (14) is operated in use of the hand prosthesis (10), the moveable component (12) rotates about the worm gear wheel 18. The moveable component (12) includes two electrical contact members (50a) and (50b) and the worm gear wheel (18) includes two electrical contact surfaces (52a) and (52b). The electrical contact members (50a), (50b) and the electrical contact surfaces (52a), (52b) are arranged to slidably contact one another as the moveable component (12) rotates about the worm gear wheel (18).
