Expandable interbody fusion cage

Abstract

An expandable interbody fusion device in one embodiment includes a cylindrical body ( 10 ) defining a hollow interior ( 17 ) for receiving bone graft or bone substitute material. The body ( 10 ) is divided into a number of branches ( 24, 26, 40 and 41 ) connected to one another at a fixed end ( 20 ) and separated at an expandable end ( 18 ). The expandable cage may be inserted in its substantially cylindrical form and may be expanded by movement of an expansion member ( 50 ) to establish lordosis of the spine. The present invention provides an expansion member ( 50 ) that interacts with the interior surfaces of the device to maintain the cage in the expanded condition and provide a large internal chamber ( 17 ) for receiving bone in-growth material. Methods for insertion of the fusion device are also disclosed.

What is claimed is:  
     
         1 . An expandable fusion cage adapted to be inserted between a pair of vertebral bodies, comprising: 
 a body having an outer bone engaging surface and an inner surface defining an internal chamber and a retaining mechanism, said body defining at least a first branch, said branch having a fixed portion connected to said body and an expandable portion movable with respect to said body, said body defining at least a second branch connected to said body; and    an expansion mechanism sized to be at least partially received within said internal chamber and to engage said expandable portion, said expansion mechanism having an outer surface adapted to engage said retaining mechanism, whereby movement of said expansion mechanism within said internal chamber urges said first branch expandable portion to move with respect to said body thereby expanding said body, said expansion mechanism moving said first branch expandable portion at a greater rate than said second branch, said expansion mechanism retained in position by engagement with said retaining mechanism of the body.    
     
     
         2 . The device of  claim 1 , wherein said bone engaging surface is an external thread.  
     
     
         3 . The device of  claim 1 , wherein said retaining mechanism is a thread pattern defined on said inner surface and said expansion mechanism includes an externally threaded plug configured for engagement with said thread pattern.  
     
     
         4 . The device of  claim 1 , wherein said retaining mechanism is an internal shoulder and said expansion mechanism is a wedge adapted to engage said shoulder.  
     
     
         5 . The device of  claim 1  wherein said body defines a third branch opposing said first branch, said third branch having a fixed portion connected to said body and an expandable portion, whereby movement of said expansion mechanism within said internal chamber urges both said first and third branches apart.  
     
     
         6 . An expandable cage adapted to be inserted between a pair of vertebral bodies, comprising: 
 a tubular body having an outer bone engaging surface and an inner surface defining an interior chamber and a retaining mechanism, said body includes a fixed end and an expandable end and further including four longitudinal channels extending between said outer surface and said inner surface and from said expandable end toward said fixed end, said channels defining an opposing first and second branches separated by opposing third and fourth branches; and    an expansion mechanism having an outer surface configured to engage said inner surface and said retaining portion, whereby said expansion mechanism is moved against said inner surface to move said expandable end to expand said body, said expansion mechanism expanding said opposing first and second branches at a substantially greater rate than said opposing third and fourth branches, and said expansion mechanism retained in position by engagement with said retaining mechanism.    
     
     
         7 . The device of  claim 6 , wherein said retaining mechanism includes at least one flange defined adjacent said inner surface and said expansion member includes a shoulder cooperable with said flange to maintain the position of said expansion member.  
     
     
         8 . The device of  claim 6 , wherein said retaining mechanism is a thread pattern and said expansion member includes a corresponding external thread pattern.  
     
     
         9 . The device of  claim 6 , wherein said bone engaging surface is an external thread.  
     
     
         10 . An expandable cage adapted to be inserted between a pair of vertebral bodies, comprising: 
 a tubular body having an outer bone engaging surface and an inner surface defining an interior chamber having a threaded inclined surface, said body defining a fixed portion and a moveable portion, said inclined surface disposed adjacent at least said moveable portion; and    an expansion member having a threaded outer surface configured to engage said threaded inclined surface, whereby said expansion member is threadedly advanced along said threaded inclined surface to move said moveable portion to expand said body and said expansion member is retained in position by engagement with said threaded inclined surface.    
     
     
         11 . The device of claims  6  or  10 , wherein said body further defines bone in-growth openings between said inner surface and said outer surface.  
     
     
         12 . The device of claims  6  or  10 , wherein said interior chamber comprises at least 50% of the volume of the device, thereby allowing a substantial amount of bone growth promoting matter to be inserted into the interior chamber.  
     
     
         13 . The device of claims  6  or  10 , wherein said expansion member defines a central opening providing communication with said interior chamber.  
     
     
         14 . An interbody fusion apparatus, comprising: 
 a hollow body having an outer bone engaging surface and an inner surface defining an internal chamber and a retaining mechanism, said body having a fixed portion and an expandable portion and defining at least a first branch and a second branch, said first branch and said second branch interconnected at said fixed portion, and said first branch moveable with respect to said second branch at said expandable portion;    an expansion member sized to be at least partially received within said internal chamber and having an outer surface adapted to engage said retaining mechanism, whereby movement of said expansion member within said internal chamber urges said first branch to move with respect to said second branch thereby expanding said expandable portion, said expansion member retained in position by engagement with said retaining mechanism of the body; and    an insertion tool having an outer sleeve adapted to engage said body to transmit compressive force and an inner shaft moveably disposed within said outer sleeve and sized to be inserted into at least a portion of said interior chamber, said inner shaft having a proximal end and a distal end, said distal end configured to removably engage said expansion member, whereby movement of said inner shaft with respect to said outer sleeve moves said expansion member in relation to said body.    
     
     
         15 . The apparatus of  claim 14 , wherein said expansion member includes a central opening having a thread pattern and said distal end of said inner shaft includes a corresponding external thread pattern.  
     
     
         16 . The apparatus of  claim 14 , wherein said expansion member includes a central hexagonal opening and said distal end of said inner shaft includes a corresponding external hexagonal shape.  
     
     
         17 . The apparatus of  claim 14 , wherein said body further defines a driving groove and said outer sleeve defines a corresponding mating driving projection.  
     
     
         18 . A method for insertion of an expandable interbody fusion device between a pair of vertebral bodies, comprising: 
 providing an expandable fusion cage having an external bone engaging surface, a movable portion and an internal cavity defining a retaining mechanism, and an expansion member sized to be at least partially received within the internal chamber and configured for engagement with the retaining mechanism and the movable portion;    inserting the expandable cage between two adjacent vertebrae;    positioning the moveable portion adjacent a vertebra;    moving the expansion member within the internal chamber and against the moveable portion to expand the cage; and    engaging the expansion member with the retaining mechanism to limit movement of the expansion member.    
     
     
         19 . The method of  claim 18 , further including packing the internal cavity with material to promote gone in-growth.