Radiolucent spinal fusion cage

Abstract

An improved bone graft is provided for human implantation, particularly such as a spinal fusion cage for implantation into the inter-vertebral space between two adjacent vertebrae. The improved spinal fusion cage includes a substrate block of high strength biocompatible material having a selected size and shape to fit the anatomical space, and a controlled porosity analogous to natural bone. The substrate block may be coated with a bio-active surface coating material such as hydroxyapatite or a calcium phosphate to promote bone ingrowth and enhanced bone fusion. Upon implantation, the fusion cage provides a spacer element having a desired combination of mechanical strength together with osteoconductivity and osteoinductivity to promote bone ingrowth and fusion, as well as radiolucency for facilitated post-operative monitoring. The fusion cage may additionally carry one or more natural or synthetic therapeutic agents for further promoting bone ingrowth and fusion.

1 - 84 . (canceled) 
     
     
         85 . An implantable prosthetic component for ingrowth attachment with adjacent spinal tissue, comprising:
 a substrate block consisting essentially of a ceramic material, and having surfaces for ingrowth attachment with adjacent spinal tissue, the substrate block comprising:
 a top surface configured for ingrowth attachment with a first vertebral body; 
 a bottom surface configured for ingrowth attachment with a second vertebral body adjacent to the first vertebral body; and 
 a substantially radiolucent body visible under X-ray imaging, but having a density allowing for passage of X-rays through the ceramic material of the body under medial-lateral X-ray imaging thus facilitating post-operative assessment of bone ingrowth from the first and second vertebral bodies into the body through the top and bottom surfaces. 
   
     
     
         86 . The implantable prosthetic component of  claim 85  wherein said substrate block includes a first, lower porosity region and a second, higher porosity region, said second region including said top and bottom exterior surfaces for ingrowth attachment with said first and second vertebral bodies. 
     
     
         87 . The implantable prosthetic component of  claim 86  wherein said second region has a porosity ranging from about 30% to about 80% by volume. 
     
     
         88 . The implantable prosthetic component of  claim 87  wherein the pore sizes in the second region range from about 100 microns to about 500 microns. 
     
     
         89 . The implantable prosthetic component of  claim 86  wherein said first region has a porosity of less than about 5% by volume. 
     
     
         90 . The implantable prosthetic component of  claim 86  wherein said first region has a relatively high strength corresponding substantially with cortical bone, and wherein said second region has a porosity corresponding substantially with cancellous bone.