an embodiment of the invention is directed to a method of creating a soft fusion between vertebral bodies . following the removal of a damaged or painful intervertebral disc ( discectomy ), the surgeon minces or macerates the disc into fragments smaller than 5 mm . disc fragments are combined with mesenchymal or progenitor cells and a rigid scaffold . these materials may also be combined with a binding agent . the cells may be autologous or allogenic and may be derived from bone , bone marrow , adipose or intervertebral disc tissue . the function of the cells is to modulate inflammation , deposit new extracellular matrix proteins , recruit endogenous cells and blood vessels by secretion and diffusion of growth factors , and remodel the consolidated tissue over time . the function of the disc fragments is to provide pro - cartilage cues to the cells present within the consolidated mass . the function of the rigid scaffold is to provide mechanical stiffness to the consolidated mass and a binding site for cells . the scaffold may be monolithic or as granules . the scaffold may be porous . the scaffold may have osteoconductive or chondroconductive properties . in an embodiment , the scaffold is composed of calcium phosphate , more specifically hydroxyapatite . the binding agent bonds the various elements together and improves the implant &# 39 ; s handling properties . an excellent example of a binding agent is fibrin , which can be derived from blood plasma , recombinant fibrinogen , or an animal source . in an embodiment , plasma protein concentrate derived from autologous platelet - poor plasma is combined with thrombin and calcium chloride and used as a binding agent . over a period of months to years , the soft fusion tissue adjusts to the appropriate structure and density based on the forces experienced at the specific spinal level . the surgeon may concurrently stabilize the vertebral bodies adjacent to the replaced disc using an interbody cage , a plate , and / or screws . the fixation mechanism should have compressive and tensile properties less than a vertebral body to provide a more natural shock absorption and flexibility at the joint . the principle of the invention is to allow the cells and tissue to remodel to conform with natural forces exhibited as described by wolff &# 39 ; s law and davis &# 39 ; law . wolff &# 39 ; s law describes the reorganization of cortical and trabecular bone tissue to become harder under repeated high stress ( e . g . weight lifters ) and less dense under low stress ( e . g . astronauts in space ). davis &# 39 ; law describes the reorganization of soft tissue and collagen matrices based on mechanical loads , analogous to wolff &# 39 ; s law . the compressive strength and young &# 39 ; s ( tensile ) modulus for common spine implant materials and tissues are listed in table 1 . table 1 sets forth the approximate compressive strength and tensile modulus for spinal implant materials and native tissues . soft fusion masses should have mechanical properties that are in the range between the native vertebral body and intervertebral disc annulus . in an embodiment of the invention , the soft fusion mass has a compressive strength and tensile modulus between the values of a total vertebral body and a disc annulus . mechanical properties stiffer than a typical vertebral body will create a focal point for stresses in the consolidated tissue , prevent flexion between the adjacent vertebral bodies , and shield stresses imparted on the vertebral bodies which can lead to bone resorption . the soft fusion mass may be implanted interbody or posterolaterally . 1 . a soft fusion mass in accordance with an embodiment of the invention was prepared using disc fragments , polymer granules , porous hydroxyapatite granules , and platelet - poor plasma ( ppp ) ( fig1 a ). the mass was loaded within a lumbar interbody cage comprised of ( peek ) polymer . 2 . a soft fusion mass was prepared using disc fragments , porous hydroxyapatite granules , and plasma protein concentrate ( ppc ) clotted with thrombin and calcium chloride ( fig1 b ). the mass was loaded within a lumbar interbody cage comprised of peek polymer . 3 . soft fusion elements of disc fragments , calcium phosphate powder , and bone marrow concentrate are packed directly into the interbody space ( fig2 ). the adjacent vertebral bodies are stabilized by posterior screws that permit micro - motion . 4 . a soft fusion mass may be implanted in the posterolateral gutters for a posterior fusion . in this example , a combination of autologous bone marrow concentrate , disc material , allograft cancellous bone chips , and ppp clotted with thrombin was implanted . 18 months after implantation , histology of the fusion biopsy demonstrates a consolidated tissue with properties of both bone and cartilage ( not shown ). in the preceding detailed description , the invention is described with reference to specific exemplary embodiments thereof and locations of use within the spine . various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims . the specification and drawings are , accordingly , to be regarded in an illustrative rather than a restrictive sense .
the invention comprises a combination of biological elements that will naturally remodel in vivo based on applied mechanical forces . the final composition will possess mechanical properties similar to cartilage or a disc , and significantly less stiff than bone or implants comprised of metals or plastics . the equilibrium stress conduction will minimize unnatural forces on neighboring healthy discs .