A surgical instrument (10, 100) includes a mount body (22, 122), a joint member, an arm, and a working end (14, 114). The mount body (22, 122) has a top portion, a distal end (24, 124), a proximal end and a bottom portion. The joint member is pivotally mounted at a distal end portion (24, 124) of the mount body (22, 122), to allow positioning of a proximal portion of an arm (12, 112) extending distally from the joint member (30, 130). The joint member (30, 130) is also configured to at least partially constrain movement of the proximal portion of the arm (12, 112) to a plane. The working end (30, 130) is mounted to a distal end portion of the arm. The surgical instrument (10, 100) can be configured as a heart stabilizer or a heart positioner. The joint member (30, 130) consists of a slotted ball (36, 136) connected to a disk member (34, 134).
