Spinal Fusion Cage, Method of Design, and Method of Use

Abstract

A fusion cage of the present invention includes a first housing portion, a second housing portion, and an insert portion adapted to be received therebetween, wherein the geometry of the fusion cage corresponds substantially to the geometry of a void into which the fusion cage is to be inserted. Also described is a novel tool for insertion of a fusion cage and a novel method for designing a fusion cage or other surgical implant for filling a void identified within a patient.

We claim: 
     
         1 . A fusion cage comprising
 a first housing portion;   a second housing portion; and   an insert portion adapted to be received between said first and second housing portions such that said first and second housing portions are held in place by said insert portion, the insert being slidingly engaged by said first and second housing portions,   wherein an external geometry of said fusion cage corresponds substantially to a geometry of a void in which said fusion cage is to be inserted.   
     
     
         2 . The fusion cage according to  claim 1  wherein each of said first and second housing portions comprises at least one aperture extending through a thickness thereof to allow bone growth through at least a portion of said fusion cage once said fusion cage has been implanted within a patient. 
     
     
         3 . The fusion cage according to  claim 1  wherein at least one of said first and second housing portions comprises a stop extending substantially perpendicularly therefrom toward a central longitudinal axis of said fusion cage, said stop preventing said insert portion from extending beyond an outer edge of said fusion cage. 
     
     
         4 . The fusion cage according to  claim 1  further comprising at least one ridge extending across at least a portion of an exterior surface of at least one of said first and second housing portions, said ridge adapted to engage a surface within a patients body, the surface being adjacent said fusion cage, in order to substantially prevent movement of said fusion once said fusion case is placed in operable position within said patient. 
     
     
         5 . The fusion cage according to  claim 1  wherein at least one of said first and second housing portions comprises a first lock portion, and further wherein said insert portion comprises a second lock portion, said first and second lock portions being adapted engage one another such that when said lock portions engage said insert portion is locked into position relative to said first and second housing portions. 
     
     
         6 . The fusion cage according to  claim 5  wherein said first lock portion is a notch and said second lock portion is a raised portion, said notch being sized and shaped to receive said raised portion, thereby locking said insert portion in place with respect to said first and second housing portions. 
     
     
         7 . The fusion cage according to claim one wherein said insert portion defines an interior space therein for allowing bone growth within said interior space. 
     
     
         8 . The fusion cage according to  claim 7  wherein said interior space of said insert portion is sized and shaped to receive a plunger portion of a tool for inserting a fusion cage into a space between adjacent vertebrae. 
     
     
         9 . A tool for inserting a fusion cage into a space between adjacent vertebrae, the tool comprising:
 a shaft portion having a first end and a second end and an upper and lower surface and having an interior space therein, the interior space extending substantially along a longitudinal axis thereof;   a plunger portion within said interior space, said plunger portion being slidingly engaged with said shaft portion;   an upper tab portion fixedly attached to an upper edge of said second end of said shaft;   a lower tab portion fixedly attached to a lower edge of said second end of said shaft;   at least one first post portion fixedly attached to said upper tab portion, said first post portion sized and shaped to engage an aperture of a housing portion of a fusion cage; and   at least one second post portion fixedly attached to said lower tab portion, said second post portion sized and shaped to engage an aperture of a housing portion of a fusion cage,   wherein said plunger portion is adapted to releasably engage an insert portion of a fusion cage.   
     
     
         10 . The tool according to  claim 9  further comprising a knob portion fixedly attached to said plunger portion for moving said plunger portion along a longitudinal axis of said shaft portion. 
     
     
         11 . The tool according to  claim 9  wherein said shaft portion comprises an upper shaft portion forming an upper portion of a length and width of said shaft portion, and a lower shaft portion forming a lower portion of a length and width of said shaft portion, said upper and lower shaft portions being removably attached to said plunger portion. 
     
     
         12 . The tool according to  claim 11  wherein said upper shaft portion further comprises a rail portion attached to an interior surface thereof, and further wherein said plunger comprises a groove portion substantially along the length of an upper surface thereof, said groove portion being sized and shaped to receive said rail portion and allow said plunger portion to slide along a length of said rail portion. 
     
     
         13 . The tool according to  claim 11  wherein said lower shaft portion further comprises a rail portion attached to an interior surface thereof, and further wherein said plunger comprises a groove portion substantially along the length of an lower surface thereof, said groove portion being sized and shaped to receive said rail portion and allow said plunger portion to slide along a length of said rail portion. 
     
     
         14 . The tool according to  claim 13  wherein said upper shaft portion further comprises a rail portion attached to an interior surface thereof, and further wherein said plunger comprises a groove portion substantially along the length of an upper surface thereof, said groove portion being sized and shaped to receive said rail portion and allow said plunger portion to slide along a length of said rail portion. 
     
     
         15 . The tool according to  claim 11  wherein said tool is disposable. 
     
     
         16 . The tool according to  claim 11  further comprising a first fin portion fixedly attached to a first end of said shaft portion and extending substantially perpendicularly therefrom, and a second fin portion fixedly attached to a first end of said shaft portion and extending substantially perpendicularly therefrom, said first fin portion extending from a substantially opposite surface of said shaft portion as said second fin portion. 
     
     
         17 . A method of designing a surgical implant, said method comprising the steps of:
 a) imaging a void to be filled by a surgical implant;   b) identifying a geometry of said void; and   c) designing a surgical implant having a geometry, at least a portion of the geometry of the surgical implant being substantially the same as at least a portion of the geometry of said void.   
     
     
         18 . The method according to  claim 17  wherein said surgical implant is a fusion cage, and further wherein said void is a space between adjacent vertebrae in a patient. 
     
     
         19 . A method of designing a surgical implant, said method comprising the steps of:
 a) identifying a void to be filled by a surgical implant;   b) creating at least one virtual image of the void using a computer imaging technique;   c) creating a three-dimensional solid model of the void using the at least one virtual image of the void created in step b), above;   d) identifying surfaces of the three-dimensional model that are normal to a patient's anatomy;   e) extracting using a computer program the normal surfaces identified in step d), above;   f) repeating steps a through e, above, iteratively a predetermined number of times to acquire surface data from a desired number of patients;   g) applying coordinate transformation to the surface data acquired in step f), above, in order to align the surfaces;   h) interpolating and combining surface data from the surfaces aligned in step g), above, to created one averaged surface;   g) designing a geometry of a surgical implant based on the average surface created in step h), above.   
     
     
         20 . The method according to  claim 19  wherein said surgical implant is a fusion cage, and further wherein said void is a space between adjacent vertebrae in a patient. 
     
     
         21 . The method according to  claim 18  wherein at least a portion of a geometry of the surgical implant designed in step g) corresponds substantially to at least a portion of a geometry of the void identified in step a).