Alignment guide for insertion of stem prosthesis

Abstract

A method and tool for inserting a prosthetic stem component in an aligned position into a prepared bone cavity. The bone is prepared by removing bone material from the bone canal and preferably also machining an entry opening of a predetermined shape and desired orientation in the bone, or marking the plane of the joint on the bone end. The tool includes an upper component that engages the top of the prosthesis stem to fix its rotational alignment, and an arm that extends to the opening in the bone and is aligned at its distal end. The upper component rides along the arm, and orients the stem with respect to the bone as the stem is inserted. The tool may include a lower element that engages the machined or marked bone and holds the arm to orient the head of the prosthesis. Optionally, the lower element may guide the distal stem. Alternatively, the guide may include an arm that simply points to, contacts or fastens at the bone end, orienting the prosthesis insertion without sighting errors. In a pointer or pin assembly which extends to an alignment point on the proximal femur, the upper portion may clamp to the femoral component head or neck, and may include a sliding bushing, that allows the guide to remain rigidly coupled as the stem is progressively advanced in the femoral canal. Articulation may be provided by a pivot mounting of the arms and bushing, and the bushing may swivel as it rides along a post, rail or pin, the lower end of which remains pointed to, or driven into, an alignment mark scribed at the medial periphery of the cut surface of the proximal femur. Alternatively, a lower alignment body may fit against a machined bone surface to fix the orientation of a linking arm in one plane, with a sliding coupling to the upper part of the prosthesis to maintain that orientation as the stem is driven down into contact with the prepared bone surface.