Intramedullary implants for replacing lost bone

Abstract

A bone transport system includes a nail having a proximal end and a distal end, the proximal end configured for securing to a first portion of bone, the distal end configured for securing to a second portion of bone. The system includes a housing having a wall with a longitudinal opening extending a length along a portion thereof The system further includes a transport sled having a length that is shorter than the length of the longitudinal opening, the transport sled configured for securing to a third portion of bone, the transport sled further configured to be moveable along the longitudinal opening. The system further includes a magnetic assembly disposed within the nail and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly moves the transport sled along the longitudinal opening. The system further includes a ribbon extending on opposing sides of the transport sled and substantially covering the longitudinal opening.

What is claimed is: 
     
       1. An implantable dynamic apparatus comprising:
 a nail having a first portion and a second portion, the first portion of the nail configured for securing to a first portion of bone, the second portion of the nail configured for securing to a second portion of bone; 
 the second portion of the nail configured to be longitudinally moveable with respect to the first portion of the nail, wherein the second portion of the nail includes an internally threaded feature; 
 a magnetic assembly configured to be non-invasively actuated by a moving magnetic field; 
 a lead screw having an externally threaded portion, the lead screw coupled to the magnetic assembly, wherein the externally threaded portion of the lead screw engages the internally threaded feature of the second portion of the nail; 
 wherein actuation of the magnetic assembly turns the lead screw, which in turn changes the longitudinal displacement between the first portion of the nail and the second portion of the nail; 
 a first abutment surface coupled to the lead screw; 
 a second abutment surface coupled to the second portion of the nail; and 
 wherein the turning of the lead screw in a first direction causes the first abutment surface to contact the second abutmentsurface, stopping the motion of the lead screw with respect to the second portion of the nail, and wherein subsequent turning of the nail in a second direction is not impeded by any jamming between the internally threaded feature and the externally threaded portion. 
 
     
     
       2. An implantable dynamic apparatus comprising:
 a nail having a proximal end and a distal end, the proximal end configured for securing to a first portion of bone, the distal end configured for securing to a second portion of bone;   a housing having a wall with a longitudinal opening extending a length along a portion thereof;   a transport sled configured for securing to a third portion of bone, the transport sled further configured to be moveable along the longitudinal opening;   a magnetic assembly disposed within the nail and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly moves the transport sled along the longitudinal opening;   a lead screw, wherein actuation of the magnetic assembly is configured to rotate the lead screw;   a first abutment surface coupled to the lead screw; and   a second abutment surface coupled to the distal end of the nail,   wherein rotation of the lead screw in a first direction causes the first abutment surface to contact the second abutment surface, stopping the motion of the lead screw with respect to the proximal end of the nail, and wherein subsequent turning of the nail in a second direction is substantially unimpeded by jamming between an internally threaded feature of the distal end of the nail and an externally threaded portion of the lead screw.   
     
     
       3. The implantable dynamic apparatus of claim 2, the transport sled comprising a length that is shorter than the length of the longitudinal opening. 
     
     
       4. The implantable dynamic apparatus of claim 2, the lead screw comprising a threaded surface having a coating thereon. 
     
     
       5. The implantable dynamic apparatus of claim 4, the coating selected from either molybdenum disulfide or amorphous diamond-like carbon. 
     
     
       6. The implantable dynamic apparatus of claim 2, wherein the externally threaded portion of the lead screw engages the internally threaded feature of the distal end of the nail. 
     
     
       7. The implantable dynamic apparatus of claim 2, the magnetic assembly comprising: a cylindrical permanent magnet, the cylindrical permanent magnet configured to be turned by a moving magnetic field. 
     
     
       8. An implantable dynamic apparatus comprising:
 a nail having a proximal end and a distal end, the proximal end configured for securing to a first portion of bone, the distal end configured for securing to a second portion of bone;   a housing having a wall with a longitudinal opening extending a length along a portion thereof;   a transport sled configured for securing to a third portion of bone, the transport sled further configured to be moveable along the longitudinal opening;   a magnetic assembly disposed within the nail and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly moves the transport sled along the longitudinal opening; and   a lead screw, wherein actuation of the magnetic assembly is configured to rotate the lead screw,   wherein the transport sled comprises a first contact surface, and a stop secured to the lead screw and having a second contact surface, wherein when the first contact surface contacts the second contact surface in response to rotation of the lead screw, the stop is configured to radially expand and prevent additional rotation of the lead screw.   
     
     
       9. An implantable dynamic apparatus comprising:
 a nail having a proximal end and a distal end, the proximal end configured for securing to a first portion of bone, the distal end configured for securing to a second portion of bone;   a housing having a wall with a longitudinal opening extending a length along a portion thereof;   a transport sled configured for securing to a third portion of bone, the transport sled further configured to be moveable along the longitudinal opening; and   a magnetic assembly disposed within the nail and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly moves the transport sled along the longitudinal opening,   wherein the magnetic assembly comprises a cylindrical permanent magnet, the cylindrical permanent magnet configured to be turned by the moving magnetic field and be held by a magnet holder rotationally coupled to the magnetic assembly.   
     
     
       10. The implantable dynamic apparatus of claim 9,
 comprising a friction applicator which couples the magnet holder to the cylindrical permanent magnet, wherein the friction applicator is configured to apply a static frictional torque to the magnet so that when a moving magnetic field couples to the cylindrical permanent magnet at a torque below the static frictional torque, the cylindrical permanent magnet and the magnet holder turn in unison, and when a moving magnetic field couples to the cylindrical permanent magnet at a torque above the static frictional torque, the cylindrical permanent magnet turns while the magnet holder remains rotationally stationary.   
     
     
       11. The implantable dynamic apparatus of claim 10, wherein the friction applicator can be adjusted over a range of static frictional torques. 
     
     
       12. The implantable dynamic apparatus implant of claim 10, wherein the friction applicator comprises a wave disc. 
     
     
       13. The implantable dynamic apparatus of claim 10, wherein the friction applicator comprises a formed flat spring. 
     
     
       14. The implantable dynamic apparatus of claim 10, wherein the cylindrical permanent magnet is a composite rare-earth magnet. 
     
     
       15. An implantable dynamic apparatus comprising:
 a nail having a proximal end and a distal end, the proximal end configured for securing to a first portion of bone, the distal end configured for securing to a second portion of bone;   a housing having a wall with a longitudinal opening extending a length along a portion thereof;   a transport sled configured for securing to a third portion of bone, the transport sled further configured to be moveable along the longitudinal opening; and   a magnetic assembly disposed within the nail and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly moves the transport sled along the longitudinal opening, and   wherein the magnetic assembly comprises a magnetic housing containing a permanent magnet therein and a biasing member interposed between the magnetic housing and the permanent magnet, wherein the magnetic housing and the permanent magnet are rotationally locked by the biasing member up to a threshold torque value.   
     
     
       16. The implantable dynamic apparatus of claim 15, wherein the permanent magnet is held by a magnet holder rotationally coupled to the magnetic assembly. 
     
     
       17. An implantable dynamic apparatus comprising:
 a nail having a proximal end and a distal end, the proximal end configured for securing to a first portion of bone, the distal end configured for securing to a second portion of bone;   a housing having a wall with a longitudinal opening extending a length along a portion thereof;   a transport sled configured for securing to a third portion of bone, the transport sled further configured to be moveable along the longitudinal opening; and   a magnetic assembly disposed within the nail and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly moves the transport sled along the longitudinal opening;   a lead screw, wherein actuation of the magnetic assembly is configured to rotate the lead screw and move the transport sled along the longitudinal opening, and wherein the lead screw is coupled to a nut moveable along a length of the lead screw in response to rotation thereof; and   a ribbon secured to the nut at one end and secured to the transport sled at an opposing end, the ribbon passing over at least one pulley, wherein movement of the nut in a first direction translates into movement of the transport sled in a second, opposing direction.   
     
     
       18. The implantable dynamic apparatus of claim 17, wherein the magnetic assembly comprises a permanent magnet configured to be turned by the moving magnetic field. 
     
     
       19. An implantable dynamic apparatus comprising:
 a first end and a second end, the first end configured for securing to a first portion of bone, the second end configured for securing to a second portion of bone:   a magnetic assembly disposed within the implantable dynamic apparatus and configured to be non-invasively actuated by a moving magnetic field, wherein actuation of the magnetic assembly rotates a lead screw operatively coupled to a nut moveable along a length of the lead screw in response to rotation thereof, the nut containing at least one nut pulley affixed thereto;   at least one exit pulley disposed within the implantable dynamic apparatus at the first end;   at least one tension line fixed relative to the first end and passing over both the at least one nut pulley and the at least one exit pulley; and   wherein the tension line is configured to be secured to a third portion of bone.   
     
     
       20. The implantable dynamic apparatus of claim 19, wherein the magnetic assembly comprises a permanent magnet configured to be turned by the moving magnetic field.