Methods and apparatus for modular and variable spinal fixation

Abstract

A method of spinal fixation includes inserting a plurality of screws into at least three vertebral bodies of a spine, the three vertebral bodies defining first and second disc spaces therebetween, and providing a spinal rod having first and second segments that exhibit different properties of flexibility. The spinal rod is connected to the plurality of screws such that the first segment is associated with the first disc space and the second segment is associated with the second disc space.

1 . A method of spinal fixation, comprising:
 inserting a plurality of screws into at least three vertebral bodies of a spine, the three vertebral bodies defining first and second disc spaces therebetween;   providing a spinal rod having first and second segments that exhibit different properties of flexibility; and   connecting the spinal rod to the plurality of screws, whereby the first segment is associated with the first disc space and the second segment is associated with the second disc space.   
     
     
         2 . The method of  claim 1 , wherein the step of providing a spinal rod includes assembling the spinal rod from the first and second segments. 
     
     
         3 . The method of  claim 2 , wherein the step of assembling includes connecting respective male and female ends of the first and second segments. 
     
     
         4 . The method of  claim 2 , wherein the step of connecting includes threading respective ends of the first and second segments. 
     
     
         5 . The method of  claim 1 , wherein the first and second segments each have different axial compression properties. 
     
     
         6 . The method of  claim 1 , wherein each of the first and second segments has a flexible component between two uniform rod portions. 
     
     
         7 . The method of  claim 6 , wherein at least one of the flexible components is a block segment made up of alternating larger and smaller square-shaped sections. 
     
     
         8 . The method of  claim 6 , wherein at least one of the flexible components is a slotted cylinder. 
     
     
         9 . The method of  claim 6 , wherein at least one of the flexible components is a two-step cylinder having larger and smaller diameter portions. 
     
     
         10 . The method of  claim 1 , further comprising adjusting mechanical properties of the spinal rod after the step of connecting the spinal rod to the plurality of screws. 
     
     
         11 . The method of  claim 10 , wherein the step of adjusting includes adjusting at least one of the first and second segments of the spinal rod by altering the properties of flexibility of said segment such that said segment is more or less rigid. 
     
     
         12 . The method of  claim 10 , wherein the step of adjusting includes replacing at least one of the first and second segments of the spinal rod with a replacement segment having more or less flexibility. 
     
     
         13 . The method of  claim 1 , wherein the different properties of flexibility of the first and second segments are established by at least one of tempering, annealing, and surface hardening the material comprising such segment. 
     
     
         14 . The method of  claim 1 , further comprising inserting at least one of an intervertebral implant, bone graft, and an artificial disc into one of the first and second disc spaces. 
     
     
         15 . A method of spinal fixation comprising:
 assembling a modular spinal rod having variable mechanical properties by selectively joining first and second rod segments each having one of uniform and variable properties of flexibility;   inserting a plurality of screws into at least three vertebral bodies of a spine, the three vertebral bodies defining first and second disc spaces therebetween; and   connecting the modular spinal rod to the plurality of screws, whereby the first rod segment is associated with the first disc space and the second rod segment is associated with the second disc space.   
     
     
         16 . The method of  claim 15 , wherein the step of assembling includes selecting the uniform and variable properties of the first and second rod segments such that the modular spinal rod possesses greater rigidity at selected positions along the modular spinal rod. 
     
     
         17 . The method of  claim 15 , further comprising inserting at least one of an intervertebral implant, bone graft, and an artificial disc into one of the first and second disc spaces. 
     
     
         18 . The method of  claim 1 , wherein at least one of the first and second rod segments having variable properties of flexibility includes a flexible component between two uniform rod portions. 
     
     
         19 . A method of spinal fixation comprising:
 inserting a plurality of screws into at least three vertebral bodies of a spine, the three vertebral bodies defining first and second disc spaces therebetween; and   connecting a first rod segment having one of uniform and variable properties of flexibility to at least two of the plurality of screws in such a manner that the first rod segment spans the first disc space;   connecting a second rod segment having one of uniform and variable properties of flexibility to at least two of the plurality of screws in such a manner that the second rod segment spans the second disc space; and   assembling the first and second rod segments together to form a modular spinal rod having variable mechanical properties.   
     
     
         20 . The method of  claim 19 , further comprising inserting at least one of an intervertebral implant, bone graft, and an artificial disc into one of the first and second disc spaces.