A trigger wire release mechanism for releasing a retained end of a prosthesis, the trigger wire release mechanism (24, 25) comprising: a prosthesis retaining device (10, 40) arranged to engage an end of the prosthesis; a trigger wire (22, 44) having a distal end and a proximal end, the distal end being arranged to selectively couple the prosthesis retaining device to the prosthesis; a control mechanism comprising an elongate body member and a guide member (93, 94), the elongate body member having a proximal end and a distal end, an exterior surface, and an interior surface, the interior surface defining a chamber extending longitudinally with the elongate body member; wherein the trigger wire proximal end is operably coupled to the guide member in the chamber and the guide member is slidably disposed between a generally distal position and a generally proximal position along the elongate body member to selectively disengage the prosthesis retaining device from the prosthesis, and wherein the control mechanism further comprises a locking mechanism (120, 130) to limit axial movement of the guide member (93, 94) along the elongate body member; characterised in that the locking mechanism comprises a stay that extends through an aperture formed in the elongate body member, the stay being coupled to the elongate body member by a biasing member that biases the stay so that a portion of the stay extends radially outwardly from the exterior surface of the elongate body member to limit the axial movement of the guide member (93, 94), wherein radial compression of the biasing member causes the stay to retract through the aperture allowing the guide member (93, 94) to traverse the stay, whereby to allow the guide member (93, 94) to move from the distal end of the elongate body member to the proximal end of the elongate body member, and to prevent the guide member (93, 94) from moving from the proximal end of the elongate body member to the distal end of the elongate body member. a prosthesis retaining device (10, 40) arranged to engage an end of the prosthesis; a trigger wire (22, 44) having a distal end and a proximal end, the distal end being arranged to selectively couple the prosthesis retaining device to the prosthesis; a control mechanism comprising an elongate body member and a guide member (93, 94), the elongate body member having a proximal end and a distal end, an exterior surface, and an interior surface, the interior surface defining a chamber extending longitudinally with the elongate body member; wherein the trigger wire proximal end is operably coupled to the guide member in the chamber and the guide member is slidably disposed between a generally distal position and a generally proximal position along the elongate body member to selectively disengage the prosthesis retaining device from the prosthesis, and wherein the control mechanism further comprises a locking mechanism (120, 130) to limit axial movement of the guide member (93, 94) along the elongate body member; characterised in that the locking mechanism comprises a stay that extends through an aperture formed in the elongate body member, the stay being coupled to the elongate body member by a biasing member that biases the stay so that a portion of the stay extends radially outwardly from the exterior surface of the elongate body member to limit the axial movement of the guide member (93, 94), wherein radial compression of the biasing member causes the stay to retract through the aperture allowing the guide member (93, 94) to traverse the stay, whereby to allow the guide member (93, 94) to move from the distal end of the elongate body member to the proximal end of the elongate body member, and to prevent the guide member (93, 94) from moving from the proximal end of the elongate body member to the distal end of the elongate body member.