Selectively expanding spine cage, hydraulically controllable in three dimensions for vertebral body replacement

Abstract

A selectively expanding spine cage has a minimized diameter in its unexpanded state that is smaller that the diameter of the neuroforamen through which it passes in the distracted spine. The cage conformably engages between the endplates of vertebrae to effectively distract the anterior disc space, stabilize the motion segments, eliminate pathologic spine motion, or effect vertebral body replacement. Angular deformities can be corrected, and natural curvatures restored and maintained. The cage enhances spinal arthrodesis by creating a rigid spine segment, or if filled with compressible substances, the cage can be used for motion preservation between vertebral bodies. Expanding selectively (anteriorly, along the vertical axis of the spine) rather than uniformly, the cage height increases and holds the vertebrae with fixation forces greater than adjacent bone and soft tissue failure forces in natural lordosis. Stability is thus achieved immediately, enabling patient function by eliminating painful motion. The cage shape intends to rest proximate to the anterior column cortices securing the desired spread and fixation, allowing for bone graft in, around, and through the implant for arthrodesis whereas for arthroplasty it fixes to endpoints but cushions the spine naturally.

1 . An apparatus for providing vertebral body replacement comprising:
 a selectively expanding spinal implant for anterior or posterior insertion through the foraminal space between opposed superior and inferior vertebral end plates of a patient, said spinal implant comprising:   a cylinder block comprising a base resting on a first end plate and two or more slave cylinders and corresponding pistons having a corrective bone engaging surface for expanding against a second end plate.   
     
     
         2 - 34 . (canceled) 
     
     
         35 . A method for providing spinal correction in three dimensions, comprising:
 a. providing an interbody implant member having
 i. a base including a first pressure applying, bone engaging surface; 
 ii. at least one extendable member cooperating with the base; 
 iii. a pressure applying member having a second pressure applying, bone engaging surface coupled to the extendable member; 
   b. removing at least part of a spinal disc between two of the patient's vertebral bodies;   c. inserting the interbody implant member between the two vertebral bodies with the first pressure applying surface of the base engaging a surface of one of the two vertebral bodies; and   d. extending the extendable member so that the pressure applying member coupled thereto engages a surface of the other vertebral body and supports the engaged vertebral body in a desired position.   
     
     
         36 . The method of  claim 35  wherein the implant member has first and second extendable members that are extended independently to provide a desired spinal correction. 
     
     
         37 . The method of  claim 36  wherein the first and second extendable members are extended independently by hydraulic actuation to provide a desired spinal correction. 
     
     
         38 . The method of  claim 35  wherein the extendable member is extended by hydraulic actuation. 
     
     
         39 . The method of  claim 38  wherein the hydraulic actuation is by hydraulic fluid. 
     
     
         40 . The method of  claim 39  wherein the hydraulic fluid is a curable polymeric material. 
     
     
         41 . The method of  claim 40  wherein the curable polymeric material is methylmethacrylate. 
     
     
         42 . The method of  claim 39  wherein the polymeric material cures to a solid state to lock the first and second extendable member in place at a desired amount of spinal correction. 
     
     
         43 . The method of  claim 38  wherein the hydraulic fluid in a incompressible fluid. 
     
     
         44 . The method of claim  32  wherein the extendable member is locked in an extended configuration. 
     
     
         45 . The method of  claim 35  wherein the base member is a cylinder block resting on a first end plate and having one or more slave cylinders and corresponding piston for expanding against a second end plate. 
     
     
         46 . The method of  claim 45  wherein a master cylinder located away from the patient and communicating hydraulically and independently with each slave cylinder for independently operating a corresponding slave piston to impart a desired spinal correction.