Spinal correction system with multi-stage locking mechanism

Abstract

In a rod fixation system of the type used to treat various spinal conditions, the same fastener is used to lock both a polyaxial screw and a rod in position. A spinal correction device according to the invention, adapted for use with a rod and a polyaxial screw having a ball-shaped head and a threaded end, comprises a head-body and a cap. The head-body includes a lower internal cavity to receive the ball-shaped head of the screw, an upper bore to receive a fixation rod therethrough, and an upper end configured to receive the cap. The head-body and the cap are configured such that a first rotation of the cap locks the polyaxial screw in position, and a second rotation of the cap locks the rod in position. In the preferred embodiment, the head-body includes one or more gaps to facilitate flexion of the head-body as a rotational torque is placed on the cap. The gap or gaps may be horizontal, vertical or other angles relative to the axis of the entrapped rod.

1 . A spinal correction device adapted for use with a rod and a polyaxial screw having a ball-shaped head and a threaded end, the device comprising: 
 a head-body and a cap, the head-body having a lower internal cavity to receive the ball-shaped head of the screw, an upper bore to receive a fixation rod therethrough, and an upper end configured to receive the cap; and    wherein the head-body and the cap are configured such that: 
 a first rotation of the cap locks the polyaxial screw in position, and  
 a second rotation of the cap locks the rod in position.  
   
     
     
         2 . The device of  claim 1 , wherein the head-body includes one or more gaps to facilitate flexion of the head-body as a rotational torque is placed on the cap.  
     
     
         3 . The device of  claim 1 , further including a compression-enhancing bushing disposed between the rod and the ball-shaped head of the screw.  
     
     
         4 . A spinal correction device adapted for use with a fixation rod, comprising: 
 a polyaxial screw having a ball-shaped head and a threaded end;    a head-body and a cap, the head-body having a lower internal cavity to receive the ball-shaped head of the screw, an upper bore to receive the fixation rod therethrough, and an upper end configured to receive the cap; and    wherein the head-body and the cap are configured such that: 
 a first rotation of the cap locks the polyaxial screw in position, and  
 a second rotation of the cap locks the rod in position.  
   
     
     
         5 . The device of  claim 4 , wherein the head-body includes one or more gaps to facilitate flexion of the head-body as a rotational torque is placed on the cap.  
     
     
         6 . The device of  claim 4 , further including a compression-enhancing bushing disposed between the rod and the ball-shaped head of the screw.  
     
     
         7 . A spinal correction device, comprising: 
 a fixation rod;    a polyaxial screw having a ball-shaped head and a threaded end;    a head-body and a cap, the head-body having a lower internal cavity to receive the ball-shaped head of the screw, an upper bore to receive the fixation rod therethrough, and an upper end configured to receive the cap; and    wherein the head-body and the cap are configured such that: 
 a first rotation of the cap locks the polyaxial screw in position, and  
 a second rotation of the cap locks the rod in position.  
   
     
     
         8 . The device of  claim 7 , wherein the head-body includes one or more gaps to facilitate flexion of the head-body as a rotational torque is placed on the cap.  
     
     
         9 . The device of  claim 7 , further including a compression-enhancing bushing disposed between the rod and the ball-shaped head of the screw.