Intramedullary Medical Devices and Methods of Manufacture

Abstract

Intramedullary medical devices (e.g., intramedullary nails) and methods for their use and manufacture are described herein. The intramedullary medical devices described herein may provide sustained compressive forces across a bone fusion site despite bone resorption processes. Through various embodiments, the intramedullary medical devices described herein may provide non-linear force curves relative to displacement. Intramedullary medical devices are described with multiple elements made of different materials. Examples of intramedullary medical devices are described with shape memory alloys.

1 . An intramedullary medical device adapted to provide contracting forces between a patient's bones, the intramedullary medical device comprising:
 (a) an encasement adapted to connect under compression at least two bone pieces;
 (i) wherein a proximal end of the encasement is adapted to be fixed within a first bone piece of the at least two bone pieces; 
 (ii) wherein a distal end of the encasement is adapted to be fixed within a second bone piece of the at least two bone pieces; 
   (b) a distal anchor element contained within the distal end of the encasement;
 (i) wherein the distal anchor element is adapted to be fixed to the second bone piece; and 
   (c) a non-linear contracting element contained within the encasement;
 (i) wherein the non-linear contracting element is connected between an internal surface of the encasement and an internal surface of the distal anchor element; 
 (ii) wherein the non-linear contracting element is adapted to provide compression between the at least two bone pieces through moving the distal anchor element within the encasement toward the proximal end of the encasement; 
 (iii) wherein the non-linear contracting element comprises a shape memory alloy adapted to exhibit a pseudo-elastic stress-strain response over a pseudo-elastic range of expansive strain imparted to the non-linear contracting element based on the distal anchor element being moved distally with respect to the proximal anchor element; 
 (iv) wherein the non-linear contracting element is further adapted to hold the at least two bone pieces in direct contact and under compression through the encasement, the distal anchor element, and the proximal anchor element, while the non-linear contracting element provides compressive forces via the pseudo-elastic stress-strain response of the shape memory alloy as a result of the expansive strain imparted on the shape memory alloy. 
   
     
     
         2 . The intramedullary medical device of  claim 1 , wherein the encasement include a unitary exterior surface adapted for interfacing with the at least two bone pieces. 
     
     
         3 . The intramedullary medical device of  claim 1 , (i) wherein the distal anchor element has a distal bone screw interface disposed within the encasement;
 (ii) wherein the encasement includes an access port positioned outside the distal bone screw interface;   (iii) wherein the access port is adapted such that the distal bone screw interface may be accessed in configurations of the non-linear contracting element having the pseudo-elastic range of expansive strain; and   (iv) wherein the non-linear contracting element is adapted such that the pseudo-elastic range of expansive strain provides through the encasement compressive forces between the at least two bone pieces.   
     
     
         4 . The intramedullary medical device of  claim 3 , wherein the access port is further adapted to restrict access to the distal bone screw for configurations of the non-linear contracting element that provide through the encasement expansive forces between the at least two bone pieces. 
     
     
         5 . The intramedullary medical device of  claim 1 , wherein the distal anchor element is adapted to allow direct access to the non-linear contracting element through the distal anchor element.