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 . A spinal fusion cage for implantation between and fusion with adjacent vertebrae, comprising:
 a substrate block having a first region of relatively high strength corresponding substantially with natural cortical bone and a second region of porous form corresponding substantially with natural cancellous bone.   
     
     
         2 . The spinal fusion cage of  claim 1  wherein said substrate block where either the first or second portion comprises a ceramic structure formed from silicon nitride, alumina, zirconia, zirconia toughened alumina, hydroxyapatite, calcium phosphate, or composition thereof. 
     
     
         3 . The spinal fusion cage of  claim 1  wherein said substrate block where either the first or second portion comprises a metallic structure formed from titanium, tantalum, stainless steel, cobalt chrome alloy, or composition thereof. 
     
     
         4 . The spinal fusion cage of  claim 1  wherein said substrate block where either the first or second portion comprises a polymeric structure formed from peek, carbon fiber reinforced polymer, PMMA, PLA (or other bioresorbable polymer), or composition thereof. 
     
     
         5 . The spinal fusion cage of  claim 1  wherein said substrate block where either the first or second portion comprises a flexible material formed from silicone, polyurethane silicone, hydrogels, elastomers, or composition thereof. 
     
     
         6 . A spinal fusion cage of  claim 1  wherein a bio-active and resorbable surface coating applied to said substrate block, said surface coating having osteoconductive and osteoinductive properties to promote interbody bone ingrowth and fusion attachment with the adjacent vertebrae. 
     
     
         7 . The spinal fusion cage of  claim 1  wherein said substrate block where the second portion is comprised of a bio-active and resorbable material having relatively high osteoconductive and osteoinductive properties, such as a hydroxyapatite or a calcium phosphate material. 
     
     
         8 . The spinal fusion cage of  claim 1  wherein said substrate block where the first portion being relatively non-resorbable or resorbable at a rate substantially less than the second portion. 
     
     
         9 . The spinal fusion cage of  claim 1  wherein the first region and the second region of the said substrate block has a porosity ranging from about 0% to about 80% by volume, and further wherein the pore size ranges from about 1 micron to about 1,500 microns. 
     
     
         10 . The spinal fusion cage of  claim 9  wherein the said first region of the said substrate block has porosity ranges from about 0% to about 50% by volume, and wherein the pore sizes range from about 1 micron to about 500 microns. 
     
     
         11 . The spinal fusion cage of  claim 9  wherein the said second region of the said substrate block has porosity ranges from about 30% to about 80% by volume, and wherein the pore sizes range from about 100 microns to about 1000 microns. 
     
     
         12 . The spinal fusion cage of  claim 9  wherein the said substrate block has a variable porosity gradient substantially mimicking natural cortical and cancellous bone. 
     
     
         13 . The spinal fusion cage of  claim 9  wherein said substrate block has a first region of relatively low porosity substantially mimicking natural cortical bone, and a second region of relatively high porosity substantially mimicking cancellous patient bone. 
     
     
         14 . The spinal fusion cage of  claim 9  wherein said first region has a porosity of less than about 5%, and wherein said second region has a porosity ranging from about 30% to about 80%. 
     
     
         15 . The spinal fusion cage of  claim 9  wherein said first region is generally disposed on the exterior of said substrate block, and said second region is generally disposed on the interior surfaces of said substrate block. 
     
     
         16 . The spinal fusion cage of  claim 9  wherein said second region is generally disposed on the exterior of said substrate block, and said first region is generally disposed on the interior surfaces of said substrate block. 
     
     
         17 . The spinal fusion cage of  claim 13  wherein said first region is generally disposed on anterior and posterior surfaces of said substrate block and further defines at least one structural load bearing strut extending through said substrate block between said anterior and posterior surfaces, said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         18 . The spinal fusion cage of  claim 17  wherein said second region is substantially exposed on medial and lateral surfaces of said substrate block. 
     
     
         19 . The spinal fusion cage of  claim 13  wherein said first region circumferentially surrounds and supports said second region, said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         20 . The spinal fusion cage of  claim 13  wherein said second region circumferentially surrounds said first region, said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         21 . The spinal fusion cage of  claim 13  wherein said first region comprises at least one structural load bearing strut extending through said substrate block, wherein said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         22 . The spinal fusion cage of  claim 1  wherein said substrate block further includes means for facilitated grasping and manipulation with a surgical instrument for implantation. 
     
     
         23 . The spinal fusion cage of  claim 6  wherein said bio-active surface coating is internally and externally applied to said substrate block. 
     
     
         24 . The spinal fusion cage of  claim 6  wherein said bio-active surface coating is selected from the group consisting of hydroxyapatite and calcium compounds. 
     
     
         25 . The spinal fusion cage of  claim 6  wherein said bio-active surface coating comprises a partially or fully amorphous osteoinductive material including a glass and osteoinductive calcium compound. 
     
     
         26 . The spinal fusion cage of  claim 6  wherein said bio-active surface coating comprises an organic coating material. 
     
     
         27 . The spinal fusion cage of  claim 26  wherein said organic coating material is selected from the group consisting of autologous bone marrow aspirates, bone morphogenic proteins, growth factors and progenitor cells, and mixtures thereof. 
     
     
         28 . The spinal fusion cage of  claim 27  wherein said progenitor cells include mesenchymal stem cells, hematopoietic cells, and embryonic stem cells. 
     
     
         29 . The spinal fusion cage of  claim 1  wherein the first region of the said substrate block is substantially radiolucent. 
     
     
         30 . The spinal fusion cage of  claim 1  wherein the second region of the said substrate block is substantially radiolucent. 
     
     
         31 . The spinal fusion cage of  claim 1  further including a therapeutic agent carried by said substrate block. 
     
     
         32 . The spinal fusion cage of  claim 31  wherein said therapeutic agent comprises a natural or synthetic osteoconductive or osteoinductive agent. 
     
     
         33 . The spinal fusion cage of  claim 1  wherein said substrate block has a rough exterior surface. 
     
     
         34 . The spinal fusion cage of  claim 1  wherein said substrate block has a ribbed exterior surface. 
     
     
         35 . The spinal fusion cage of  claim 1  wherein said substrate block has a laterally open bore formed therein, and further including an osteoconductive material supported within said bore. 
     
     
         36 . The spinal fusion cage of  claim 35  wherein said osteoconductive material comprises morselized bone graft material. 
     
     
         37 . The spinal fusion cage of  claim 1  wherein the pores formed within the second region of the said substrate block are in substantially open fluid communication sufficient to transmit fluid pressure therebetween. 
     
     
         38 . The spinal fusion cage of  claim 1  wherein the pores formed within the first region of the said substrate block may be in substantially open fluid communication sufficient to transmit fluid pressure therebetween. 
     
     
         39 . A spinal fusion cage for implantation between and fusion with adjacent vertebrae, comprising:
 a substrate block having a relatively high strength corresponding substantially with natural cortical and cancellous bone; and   a bio-active and relatively rapidly resorbable surface coating applied to said substrate block, said surface coating having osteoconductive and osteoinductive properties to promote interbody bone ingrowth and fusion attachment with the adjacent vertebrae;   said substrate block being relatively nonresorbable or resorbable at a rate substantially less than said surface coating.   
     
     
         40 . A spinal fusion cage for implantation between and fusion with adjacent vertebrae, comprising:
 a substrate block including at least one load bearing strut having high strength structural characteristics; and   a bio-active and resorbable surface coating carried by said at least one strut, said surface coating having osteoconductive and osteoinductive properties to promote interbody bone ingrowth and fusion attachment with adjacent patient bone.   
     
     
         41 . The spinal fusion cage of  claim 40  wherein said at least one strut substantially mimics the structural characteristics of natural bone. 
     
     
         42 . The bone graft of  claim 40  wherein said at least one strut is formed from a porous material. 
     
     
         43 . A spinal fusion cage for implantation between and fusion with adjacent vertebrae, comprising:
 a first region formed by load bearing anterior and posterior wall connected by at least one load bearing strut; and   a relatively porous second region comprising the superior, inferior, and lateral aspects.   
     
     
         44 . The spinal fusion cage of  claim 43  wherein said substrate block where either the first or second portion comprises a ceramic structure formed from silicon nitride, alumina, zirconia, zirconia toughened alumina, hydroxyapatite, calcium phosphate, or composition thereof. 
     
     
         45 . The spinal fusion cage of  claim 43  wherein said substrate block where either the first or second portion comprises a metallic structure formed from titanium, tantalum, stainless steel, cobalt chrome alloy, or composition thereof. 
     
     
         46 . The spinal fusion cage of  claim 43  wherein said substrate block where either the first or second portion comprises a polymeric structure formed from peek, carbon fiber reinforced polymer, PMMA, PLA (or other bioresorbable polymer), or composition thereof. 
     
     
         47 . The spinal fusion cage of  claim 43  wherein said substrate block where either the first or second portion comprises a flexible material formed from silicone: polyurethane silicone, hydrogels, elastomers, or composition thereof. 
     
     
         48 . The spinal fusion cage of  claim 43  wherein a bio-active and resorbable surface coating applied to said substrate block, said surface coating having osteoconductive and osteoinductive properties to promote interbody bone ingrowth and fusion attachment with the adjacent vertebrae. 
     
     
         49 . The spinal fusion cage of  claim 43  wherein said substrate block where the second portion is comprised of a bio-active and resorbable material having relatively high osteoconductive and osteoinductive properties, such as a hydroxyapatite or a calcium phosphate material. 
     
     
         50 . The spinal fusion cage of  claim 43  wherein said substrate block where the first portion being relatively non-resorbable or resorbable at a rate substantially less than the second portion. 
     
     
         51 . The spinal fusion cage of  claim 43  wherein the first region and the second region of the said substrate block has a porosity ranging from about 0% to about 80% by volume, and further wherein the pore size ranges from about 1 micron to about 1,500 microns. 
     
     
         52 . The spinal fusion cage of  claim 51  wherein the said first region of the said substrate block has porosity ranges from about 0% to about 50% by volume, and wherein the pore sizes range from about 1 micron to about 500 microns. 
     
     
         53 . The spinal fusion cage of  claim 51  wherein the said second region of the said substrate block has porosity ranges from about 30% to about 80% by volume, and wherein the pore sizes range from about 100 microns to about 1000 microns. 
     
     
         54 . The spinal fusion cage of  claim 51  wherein the said substrate block has a variable porosity gradient substantially mimicking natural cortical and cancellous bone. 
     
     
         55 . The spinal fusion cage of  claim 51  wherein said substrate block has a first region of relatively low porosity substantially mimicking natural cortical bone, and a second region of relatively high porosity substantially mimicking cancellous patient bone. 
     
     
         56 . The spinal fusion cage of  claim 51  wherein said first region has a porosity of less than about 5%, and wherein said second region has a porosity ranging from about 30% to about 80%. 
     
     
         57 . The spinal fusion cage of  claim 51  wherein said first region is generally disposed on the exterior of said substrate block, and said second region is generally disposed on the interior surfaces of said substrate block. 
     
     
         58 . The spinal fusion cage of  claim 51  wherein said second region is generally disposed on the exterior of said substrate block, and said first region is generally disposed on the interior surfaces of said substrate block. 
     
     
         59 . The spinal fusion cage of  claim 55  wherein said first region is generally disposed on anterior and posterior surfaces of said substrate block and further defines at least one structural load bearing strut extending through said substrate block between said anterior and posterior surfaces, said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         60 . The spinal fusion cage of  claim 59  wherein said second region is substantially exposed on medial and lateral surfaces of said substrate block. 
     
     
         61 . The spinal fusion cage of  claim 55  wherein said first region circumferentially surrounds and supports said second region, said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         62 . The spinal fusion cage of  claim 55  wherein said second region circumferentially surrounds said first region, said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         63 . The spinal fusion cage of  claim 55  wherein said first region comprises at least one structural load bearing strut extending through said substrate block, wherein said second region including an extended exposed surface area for contacting the adjacent vertebrae. 
     
     
         64 . The spinal fusion cage of  claim 43  wherein said substrate block further includes means for facilitated grasping and manipulation with a surgical instrument for implantation. 
     
     
         65 . The spinal fusion cage of  claim 48  wherein said bio-active surface coating is internally and externally applied to said substrate block. 
     
     
         66 . The spinal fusion cage of  claim 48  wherein said bio-active surface coating is selected from the group consisting of hydroxyapatite and calcium compounds. 
     
     
         67 . The spinal fusion cage of  claim 48  wherein said bio-active surface coating comprises a partially or fully amorphous osteoinductive material including a glass and osteoinductive calcium compound. 
     
     
         68 . The spinal fusion cage of  claim 48  wherein said bio-active surface coating comprises an organic coating material. 
     
     
         69 . The spinal fusion cage of  claim 68  wherein said organic coating material is selected from the group consisting of autologous bone marrow aspirates, bone morphogenic proteins, growth factors and progenitor cells, and mixtures thereof. 
     
     
         70 . The spinal fusion cage of  claim 69  wherein said progenitor cells include mesenchymal stem cells, hematopoietic cells, and embryonic stem cells. 
     
     
         71 . The spinal fusion cage of  claim 43  wherein the first region of the said substrate block is substantially radiolucent. 
     
     
         72 . The spinal fusion cage of  claim 43  wherein the second region of the said substrate block is substantially radiolucent. 
     
     
         73 . The spinal fusion cage of  claim 43  further including a therapeutic agent carried by said substrate block. 
     
     
         74 . The spinal fusion cage of  claim 73  wherein said therapeutic agent comprises a natural or synthetic osteoconductive or osteoinductive agent. 
     
     
         75 . The spinal fusion cage of  claim 43  wherein said substrate block has a rough exterior surface. 
     
     
         76 . The spinal fusion cage of  claim 43  wherein said substrate block has a ribbed exterior surface. 
     
     
         77 . The spinal fusion cage of  claim 43  wherein said substrate block has a laterally open bore formed therein, and further including an osteoconductive material supported within said bore. 
     
     
         78 . The spinal fusion cage of  claim 77  wherein said osteoconductive material comprises morselized bone graft material. 
     
     
         79 . The spinal fusion cage of  claim 43  wherein the pores formed within the second region of the said substrate block are in substantially open fluid communication sufficient to transmit fluid pressure therebetween. 
     
     
         80 . The spinal fusion cage of  claim 43  wherein the pores formed within the first region of the said substrate block may be in substantially open fluid communication sufficient to transmit fluid pressure therebetween. 
     
     
         81 . A spinal fusion cage for implantation between and fusion with adjacent vertebrae, comprising:
 a substrate block having a relatively high strength corresponding substantially with natural cortical and cancellous bone; and   a bio-active and relatively rapidly resorbable surface coating applied to said substrate block, said surface coating having osteoconductive and osteoinductive properties to promote interbody bone ingrowth and fusion attachment with the adjacent vertebrae;   said substrate block being relatively nonresorbable or resorbable at a rate substantially less than said surface coating.   
     
     
         82 . A spinal fusion cage for implantation between and fusion with adjacent vertebrae, comprising:
 a substrate block including at least one load bearing strut having high strength structural characteristics; and   a bio-active and resorbable surface coating carried by said at least one strut, said surface coating having osteoconductive and osteoinductive properties to promote interbody bone ingrowth and fusion attachment with adjacent patient bone.   
     
     
         83 . The spinal fusion cage of  claim 82  wherein said at least one strut substantially mimics the structural characteristics of natural bone. 
     
     
         84 . The bone graft of  claim 82  wherein said at least one strut is formed from a porous material.