Intervertebral fusion device utilizing multiple mobile uniaxial and bidirectional screw interface plates

Abstract

This invention relates to a spinal fusion system and method for use as a prosthetic implant. The system and method includes a housing dimensioned to be situated between adjacent spinal bones, such as adjacent vertebrae. The housing cooperates with the spinal bones to define at least one or a plurality of graft areas for receiving graft material, which may be pre-packed into the cage or inserted anteriorly into the housing during a surgical operation such as a vertebrectomy or discectomy. A housing may have various features such as migration preventers to prevent the housing from migrating posteriorly towards a spinal column and can be used with a cover that permits the housing to “float” relative thereto. Screws are provided in one embodiment and are dimensioned or configured to lock against each other to retain the screws and, consequently, the cover in place.

What is claimed is: 
     
         1 . A spinal implant comprising:
 a cage having a plurality of windows; and   a plurality of plate elements, each of said plurality of plate elements having an aperture for receiving a screw;   said plurality of plate elements and said cage being adapted to permit said plurality of plate elements to move independently on said cage.   
     
     
         2 . The spinal implant as recited in  claim 1  wherein said plurality of plate elements each have an axis of movement that is generally parallel. 
     
     
         3 . The spinal implant as recited in  claim 1  wherein each of said plurality of plate elements have an axis of movement that is generally perpendicular to a plane of said cage. 
     
     
         4 . The spinal implant as recited in  claim 1  wherein each of said plurality of plate elements move with respect to said cage along an axis that is generally perpendicular to a plane of said cage. 
     
     
         5 . The spinal implant as recited in  claim 1  wherein each of said plurality of plate elements comprises a wall that defines said aperture, said aperture causing said screw to traverse each of said plurality of plate elements at a predetermined angle with respect to said cage. 
     
     
         6 . The spinal implant as recited in  claim 5  wherein said predetermined angle is between 30-80 degrees. 
     
     
         7 . The spinal implant as recited in  claim 1  wherein said plurality of plate elements comprises a first plate and a second plate that are slidably received on said cage, said first plate having a first wall that defines a first aperture having a first aperture axis and said second plate having a second wall that defines a second aperture having a second aperture axis, said first and second apertures receiving a first screw and a second screw, respectively; said first and second screws traversing said first and second plates at a first predetermined angle and a second predetermined angle, respectively. 
     
     
         8 . The spinal implant as recited in  claim 7  wherein each of said first and second predetermined angles is a fixed angle trajectory that falls between 30-80 degrees. 
     
     
         9 . The spinal implant as recited in  claim 7  wherein said first and second aperture axes diverge so that said first screw can be screwed into a first vertebrae and said second screw can be screwed into a second vertebrae after said cage is received between said first and second vertebrae. 
     
     
         10 . The spinal implant as recited in  claim 1  wherein said each of said screws that are received in said plurality of plate elements comprises a lock for locking into said plurality of plate elements. 
     
     
         11 . The spinal implant as recited in  claim 7  wherein each of said first and second screws that are received in said first plate and said second plate, respectively, comprises a lock for locking into said plurality of plate elements. 
     
     
         12 . The spinal implant as recited in  claim 11  wherein said lock is a tapered thread. 
     
     
         13 . The spinal implant as recited in  claim 7  wherein said first wall comprises a first female thread and said second wall comprises a second female thread, each of said first screw and said second screw comprising a tapered male thread for mating with said first and second female threads. 
     
     
         14 . The spinal implant as recited in  claim 1  wherein said cage and said plurality of plate elements are adapted to permit controlled motion of said plurality of plate elements in said cage. 
     
     
         15 . The spinal implant as recited in  claim 14  wherein said controlled motion is axial, sliding motion of said plurality of plate elements in said cage. 
     
     
         16 . The spinal implant as recited in  claim 15  wherein said plurality of plate elements comprise a first plate comprising a first side and a second side and a second plate having a third side and a fourth side, said cage comprising a first cage surface and a generally opposed second cage surface that cooperate to define a first cage window, said cage further comprising a third cage surface and a fourth cage surface that cooperate to define a second cage window, said first and second plates being received in said first and second cage windows, respectively. 
     
     
         17 . The spinal implant as recited in  claim 16  wherein said first side and said second side of said first plate cooperates with said first cage surface and said second cage surface, respectively, to define a first joint and a second joint; said third side and said fourth side of said second plate cooperate with said third cage surface and said fourth cage surface, respectively, to define a third joint and a fourth joint. 
     
     
         18 . The spinal implant as recited in  claim 17  wherein the first joint, second joint, third joint and fourth joint are adapted to retain said first plate and said second plate in said cage and also permit relative movement of said first and second plates and said cage. 
     
     
         19 . The spinal implant as recited in  claim 18  wherein said first joint, second joint, third joint and fourth joint comprise at least one of a rail and groove joint, a dovetail joint, a groove and an interrupted boss, notch or projection. 
     
     
         20 . The spinal implant as recited in  claim 18  wherein each of said first side and said first cage surface comprises at least one of a first projection or a first groove and each of said second side and said second cage surface comprises at least one of a complementary second groove or a complementary second projection, respectively, that mates with and receives said first projection or said first groove, respectively. 
     
     
         21 . The spinal implant as recited in  claim 20  wherein each of said third side and said fourth side comprises at least one of a third projection or a third groove and each of said third cage surface and said fourth cage surface comprises at least one of a complementary second groove or a complementary second projection, respectively, that mates with and receives said third projection or said third groove, respectively. 
     
     
         22 . The spinal implant as recited in  claim 1  wherein each of said plurality of plate elements comprises a plate lock for locking a first and a second plate onto said cage. 
     
     
         23 . The spinal implant as recited in  claim 22  wherein said plate lock comprises a notch and a mating boss. 
     
     
         24 . The spinal implant as recited in  claim 23  wherein said plurality of plate elements comprises a first plate and a second plate comprising said notch and said cage comprises said mating boss. 
     
     
         25 . The spinal implant as recited in  claim 1  wherein said cage is generally W-shaped. 
     
     
         26 . The spinal implant as recited in  claim 25  wherein said cage comprises a first leg portion, a second leg portion, a third leg portion and a joining portion joining said first, second and third leg portions. 
     
     
         27 . The spinal implant as recited in  claim 26  wherein at least said first and second leg portions are at least one of elastic or resilient so that they can move away from said third leg portion when a first plate and a second plate, respectively, are mounted on said cage. 
     
     
         28 . The spinal implant as recited in  claim 1  wherein each of said plurality of plate elements and said cage have an interfitting joint for permitting said plurality of plate elements to move relative to said cage after said plurality of plate elements are mounted on said cage, said interfitting joint also retaining said plurality of plate elements on said cage. 
     
     
         29 . The spinal implant as recited in  claim 28  wherein said interfitting joint permits sliding movement of each of said plurality of plate elements on said cage. 
     
     
         30 . The spinal implant as recited in  claim 29  wherein said sliding movement of each of said plurality of plate elements is along its longitudinal axis. 
     
     
         31 . The spinal implant as recited in  claim 30  wherein said sliding movement is generally parallel to an axis of said cage. 
     
     
         32 . The spinal implant as recited in  claim 1  wherein said spinal implant comprises a tool having a lock for locking said plates in said cage during insertion of said cage in a patient. 
     
     
         33 . The spinal implant as recited in  claim 32  wherein lock is a plurality of projections that prevent said plates from moving in said cage during such insertion. 
     
     
         34 . A spinal implant comprising:
 a cage;   a first plate; and   a second plate;   said cage, said first plate and said second plate having a plurality of interfitting joints for permitting said first and second plates to move relative to said cage after said first and second plates are mounted on said cage and a lock or retainer for locking or retaining, respectively, said first and second plates on said cage after they are mounted thereto.   
     
     
         35 . An apparatus for surgical use in humans, comprising:
 a housing for insertion between vertebrae in a human spine;   a recess in said housing for receiving bone graft material;   a cover securable to at least one of the adjacent vertebrae and being configured to block egress of the bone graft material from said recess; and   said cover and said housing being slidably engaged one to the other.