Flexible implant using partially demineralized bone

Abstract

Implantable devices useful for creating bony fusion particularly in intervetebral spinal fusion. The device is formed of bone and has an at least partially demineralized portion between two rigid bone portions creating an area of flexibility. In one application, the area of flexibility may be used to move the device between a reduced size insertion configuration and an expanded implanted configuration. In another use, the area of flexibility may be useful to dampen shock applied to the implant. A method is also disclosed for making the implants and inserting the implants into an intervertebral disc space to promote interbody fusion.

What is claimed is:  
     
         1 . An implant, comprising: 
 a first bone portion,    a second bone portion, and    a flexible bone portion joining said first bone portion and said second bone portion, said flexible bone portion permitting movement of said first bone portion in relation to said second bone portion.    
     
     
         2 . The implant of    claim 1   , wherein said flexible bone portion is at least partially demineralized bone.  
     
     
         3 . The implant of    claim 1   , wherein said flexible bone portion includes an area of completely demineralized bone.  
     
     
         4 . The implant of    claim 1   , wherein said first portion includes an upper bearing surface and a lower bearing surface separated by a first height, and said second bone portion includes an upper bearing surface and a lower bearing surface separated by a second height, said first and second heights adapted to maintain spacing between adjacent bone.  
     
     
         5 . The implant of    claim 4   , wherein said first height and said second height are substantially equal.  
     
     
         6 . The implant of    claim 4   , wherein each of said upper and lower bearing surfaces includes a bone engaging surface to inhibit expulsion from a disc space between two adjacent vertebra.  
     
     
         7 . The implant of    claim 1   , wherein said implant is a spinal fusion device and said first and second bone portions are adapted to maintain a desired spacing between a first vertebral body and a second vertebral body.  
     
     
         8 . The implant of    claim 7   , wherein said first and second bone portions have corresponding tapered bearing surfaces to provide an implant having a spacing height gradually increasing from a first end to an opposite second end, wherein said implant is adapted for use in maintaining lordosis.  
     
     
         9 . The implant of    claim 1   , wherein said first bone portion, said second bone portion, and said flexible bone portion are formed of a single bone segment.  
     
     
         10 . An implant, comprising: 
 a bone segment having a cortical bone portion extending between a first bearing surface and a second bearing surface, said portion being at least partially demineralized to create a flexible segment disposed between said first and second bearing surfaces.    
     
     
         11 . The implant of    claim 10   , wherein said bone segment is a ring shaped bone segment, said bone segment includes a cut opposite said flexible segment, said cut dividing said bone segment into a first portion extending between said cut and said flexible segment and an opposite second portion extending between said cut and said flexible segment.  
     
     
         12 . The implant of    claim 10   , wherein said first bearing surface is adapted to engage an upper vertebral body and said second bearing surface is adapted to engage an adjacent lower vertebral body, said flexible segment disposed between said first and second bearing surfaces to transmit forces therebetween, wherein said flexible segment functions as a shock absorber.  
     
     
         13 . A spinal fusion implant adapted for insertion into the space between adjacent first and second vertebral bodies, comprising: 
 a first bone portion having a first bearing surface for engaging a first vertebral body;    a second bone portion having a second bearing surface for engaging a second vertebral body; and    at least one flexible portion disposed between said first and second bone portions, said flexible portion permitting movement between said first bone portion and said second bone portion.    
     
     
         14 . The spinal fusion implant of    claim 13   , wherein said first bone portion has a third bearing surface opposite said first bearing surface, said third bearing surface adapted for engaging said second vertebral body and said second bone portion has a fourth bearing surface opposite said second bearing surface, said fourth bearing surface adapted for engaging said first vertebral body, wherein said first and second bone portions cooperate to maintain the space between the first and second vertebral bodies.  
     
     
         15 . The spinal fusion implant of    claim 13   , wherein flexible portion acts as a shock absorber between said first and second vertebral bodies.  
     
     
         16 . The spinal fusion implant of    claim 13   , wherein the implant has a proximal end and an opposite distal end, and said flexible portion is disposed adjacent said proximal end.  
     
     
         17 . The implant of    claim 16   , further including a second flexible portion disposed adjacent said distal end and extending between said first and second bone portions.  
     
     
         18 . The implant of    claim 17   , wherein said bearing surface and said second bearing surface including cooperating thread patterns permitting threaded insertion of the implant into the space between the first and second vertebral bodies.  
     
     
         19 . The implant of    claim 15   , wherein said implant is formed of a single segment of bone.  
     
     
         20 . A method of preparing a flexible bone implant, comprising: 
 providing a rigid bone segment;    delineating an intermediate portion of the bone segment; and    at least partially demineralizing the intermediate portion of the bone to create a flexible segment between adjacent sections of rigid bone.    
     
     
         21 . The method of    claim 20   , wherein said at least partially demineralizing includes exposing said intermediate portion to a demineralizing fluid.  
     
     
         22 . The method of    claim 21   , further including limiting contact of bone adjacent the intermediate portion with the demineralizing fluid.  
     
     
         23 . The method of    claim 22   , wherein said limiting utilizes hydrostatic pressure to limit the movement of the demineralizing fluid into the bone adjacent the intermediate portion.  
     
     
         24 . The method of    claim 20   , further including forming a bone-engaging surface on the implant.  
     
     
         25 . The method of    claim 24   , wherein said bone engaging surface is configured to prevent movement of the implant.  
     
     
         26 . A method of inserting an interbody fusion implant made of bone, comprising: 
 providing an insertion tube and an implant formed of bone and having a first portion, a second portion and a central flexible portion joining the first and second portions;    positioning the insertion tube adjacent a disc space between two vertebra;    inserting the implant into the insertion tube;    advancing the implant through the insertion tube and into the disc space;    moving the first portion with respect to the second portion.    
     
     
         27 . A method of implanting a bone implant for spinal spacing, comprising: 
 providing a bone implant with at least a portion thereof moveable from a reduced insertion configuration to an expanded spacing configuration;    moving the implant to the reduced insertion configuration;    delivering the implant to the disc space in the reduced insertion configuration; and    positioning the implant in the expanding spacing configuration.    
     
     
         28 . The method of    claim 27   , wherein said implant is at least partially resilient and said moving includes compressing the implant with a compressing device.  
     
     
         29 . The method of    claim 28   , wherein said delivering is accomplished by a tube having an internal passageway configured to receive said implant in the reduced insertion configuration.