Proximal self-locking long bone prosthesis
A method for arthroplasty includes using a self-locking prosthesis that has a member structured to transfer a load produced by the weight of a patient to a bone. An expandable bone-locking portion that is integral to the member includes a shape-memory material and expands to produce a locking force. A portion of the bone is removed to form an aperture in the bone. The bone-locking portion is inserted into the aperture, and a temperature increase causes a change from a contracted state to an expanded state resulting in expansion of the bone-locking portion so as to contact the inner surface. The expanding is sufficient to create a locking force at the junction between the inner surface and the bone-locking portion of the prosthesis and the majority of the locking force is applied at or above the metaphysis. The length/width ration of the prosthesis may be less than or equal to 5. The resulting reconstructed long-bone may have improved primary and long-term stability.
1. A weight-bearing femoral stem hip implant for insertion into a surgically created aperture in a femur, the implant comprising:
a non-hollow stem made of shape memory material, the stem being adapted for insertion into the aperture and being a single-branch without a central gap, the stem further having a longitudinal axis and at least a portion of the shape memory material within a proximal portion of the stem being in a compressed state, the compressed shape memory material within the proximal portion of the stem having a cross section perpendicular to the longitudinal axis of the stem, the shape memory material having been compressed by application of a plurality of opposing compressive forces to the shape memory material at a temperature below an austenitic finish temperature of the shape memory material so that the cross section of the shape memory material expands through shape memory effect via the formation of austenite in response to a temperature increase after insertion into the aperture so as to cause a locking-force to be exerted against an inner surface of the aperture and at a proximal portion of the aperture, the locking force being sufficient to stabilize the implant in the aperture; and
a connection feature integral to the stem and adapted for connection to an acetabular ball;
wherein the femoral stem hip implant is monolithic.
2. A hip implant according to claim 1 , wherein at least 70% of the cross section is occupied by shape memory material.
3. A hip implant according to claim 1 , wherein the entirety of the cross section is occupied by shape memory material.
4. A hip implant according to claim 1 , wherein the hip implant is adapted to apply a majority of the locking-force to regions of the femur that are no more distal than a metaphysis of the femur.
5. A hip implant according to claim 1 , wherein the hip implant is adapted to apply a majority of the locking-force to regions of the femur that are no more distal than a most distal point of a lesser trochanter of the femur.
6. A hip implant according to claim 1 , wherein the hip implant includes at least one of a porous surface coating, a drug coating, and a collagen coating.
7. A hip implant according to claim 1 , wherein the plurality of opposing compressive forces are applied by at least one of a forging process and a pressing process.
8. A hip implant according to claim 1 , wherein certain regions of the compressed shape memory material have been compressed to varying degrees such that in response to the temperature increase a varying expansion along the length of the shape memory material results.
9. A hip implant according to claim 1 , wherein the locking force exerted by the hip implant promotes bone remodeling and osseointegration.
10. A prosthesis according to claim 9 , wherein the hip implant includes a textured or porous surface.
11. A hip implant according to claim 1 , wherein the shape memory material is a titanium-niobium alloy.