Proximally Self-Locking Long Bone Prosthesis

Abstract

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 method comprising:
 providing a sterile prosthesis having a member structured to transfer a load produced by the weight of a patient to a bone, and an expandable bone-locking portion that is integral to the member, the bone-locking portion comprising a shape-memory material having a contracted state and an expanded state, wherein expansion of the shape-memory material produces a locking force;   removing a portion of the bone so as to form an aperture in the bone, the aperture defining an inner surface of exposed bone and allowing access to a metaphysis of the bone;   inserting the bone-locking portion of the prosthesis into the aperture,   wherein a temperature increase causes a change from the contracted state to the expanded state resulting in expansion of the bone-locking portion so as to contact the inner surface,   wherein 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   wherein the majority of the locking force is applied at or above the metaphysis.   
   
   
       2 . A method according to  claim 1 , wherein the locking creates a seal sufficient to exclude particles and debris from entering the junction. 
   
   
       3 . A method according to  claim 1 , further comprising positioning a deformable gap-filling material at the interface of the bone-locking portion of the prosthesis and the inner surface of the aperture so that upon the expanding of the bone-locking portion, the gap-filling material is securely held in the junction. 
   
   
       4 . A method according to  claim 1 , wherein the bone is a femur, the prosthesis is a femoral implant and the majority of the locking force is applied to a region of the bone no more distal than the most distal point of the lesser trochanter. 
   
   
       5 . A method according to  claim 4 , wherein the majority of the locking force is applied to the calcar femorale. 
   
   
       6 . A method according to  claim 1 , wherein the prosthesis extends into the aperture by less than or equal to 5 inches. 
   
   
       7 . A method according to  claim 1 , wherein the shape memory material is Nitinol. 
   
   
       8 . A method according to  claim 7 , wherein the shape memory material expands radially by one of less than 8%, 5% and 1%. 
   
   
       9 . A method according to  claim 1 , further comprising maintaining the flexibility of the diaphysis by using a prosthesis with a truncated shaft. 
   
   
       10 . A method according to  claim 9 , wherein after insertion, the shaft does not extend into the diaphysis of the bone. 
   
   
       11 . A method according to  claim 1 , further comprising maintaining the flexibility of the diaphysis by using a prosthesis with distal shaft region comprising a material having a flexibility greater than that of stainless steel so as to prevent stress shielding. 
   
   
       12 . A method according to  claim 1 , further comprising positioning a deformable gap-filling material at the interface of the bone-locking portion of the prosthesis and the inner surface of the aperture. 
   
   
       13 . A method according to  claim 1 , further comprising preventing rotation of the prosthesis after implantation wherein the preventing rotation includes preparing an eccentric aperture and using a prosthesis with a complementary eccentric cross-section. 
   
   
       14 . A method according to  claim 1 , further comprising preventing rotation of the prosthesis after implantation, wherein the preventing rotation includes using an aperture that includes a plurality of facets and the bone-locking portion includes a plurality of corresponding facets. 
   
   
       15 . A method according to  claim 1 , further comprising preventing rotation of the prosthesis after implantation wherein the preventing rotation includes using a bone-locking portion having one of a barb, tooth, tang, flute and rib. 
   
   
       16 . A method according to  claim 1 , wherein the bone-locking portion is characterized by a cross-section, the majority of which is composed of shape-memory material. 
   
   
       17 . A prosthesis for use in an arthroplasty, the prosthesis comprising:
 a shaft member having a proximal end and a distal end, the shaft member sized for insertion into a surgically created aperture in a bone;   a connection feature disposed in proximity to the proximal end of the shaft member for attachment of a prosthetic ball;   an expandable bone-locking portion integral to the shaft member comprising a shape-memory material adapted for insertion into an aperture created in a bone, the shape memory material adapted to radially expand through the formation of austenite in response to a temperature increase after insertion into the aperture so as to provide a locking-force sufficient to stabilize the prosthesis in the aperture, the prosthesis being characterized by a length and a width, wherein the ratio of length/width is less than or equal to 5, wherein the prosthesis is sterile.   
   
   
       18 . A prosthesis according to  claim 17 , wherein the shaft member defines a central axis and the shape memory material in the bone-locking portion is compressed prior to use by an application of force having a component that is orthogonal to the central axis. 
   
   
       19 . A prosthesis according to  claim 17 , wherein the prosthesis is adapted to provide a majority of the locking-force to regions of the bone that are no more distal than a metaphysis of the bone that is exposed by the aperture. 
   
   
       20 . A reconstructed femur comprising:
 a resected long bone having a metaphysis, the bone further having a surgically-created aperture at a proximal end, the bone defining an axis extending from a proximal end to a distal end;   a sterile prosthesis embedded in the aperture and comprising a bone-locking portion that includes a shape memory alloy characterized by an at least partially martensitic state at a first temperature and an at least partially austenitic state at a second temperature, the bone-locking portion having a contracted shape at the first temperature and an expanded state at the second temperature, the bone-locking portion of the embedded prosthesis being in the expanded state so as to apply a locking force to the bone; and   a ball, attached to the prosthesis, for insertion into an acetabulum,   wherein a majority of the locking force is applied to regions of the bone that are no more distal with respect to the axis than the metaphysis.