Pedicle screw with detachable polyaxial head

Abstract

A pedicle screw device for fixating at least two adjacent vertebral bodies is presented. The device consists of a bone screw which is implanted into the pedicle of a vertebral body. A second bone screw is implanted into the pedicle of a second vertebral body. A polyaxial head is then inserted over each bone screw. The polyaxial heads can then be slid into a retaining position on the bone screw, allowing them to rotate about the spherical portion of the bone screw. The polyaxial heads are then attached to one another with a rod. Finally, a locking screw is inserted into the polyaxial heads to force the rod against the bone screw as well as the polyaxial head, locking them in place. The rod also serves to prevent the polyaxial head from disconnecting from the bone screw.

1 . A polyaxial head comprising:
 a vertical screw head channel formed within a first lateral side of the polyaxial head;   a screw head aperture formed within a second lateral side of the polyaxial head;   a horizontal screw head channel connecting the vertical screw head channel and the screw head aperture, the horizontal screw head channel being defined by a first side wall and a second side wall; and   a pair of retaining tabs comprising a first retaining tab formed in the first side wall and a second retaining tab formed in the second side wall, wherein the pair of retaining tabs are configured to flex outward to limit movement of a bone screw between a first position where the bone screw is in the horizontal screw head channel and a second position where the bone screw is reversibly secured by the pair of retaining tabs within the screw head aperture.   
     
     
         2 . The polyaxial head of  claim 1 , wherein the first retaining tab and the second retaining tab are aligned across the horizontal screw head channel. 
     
     
         3 . The polyaxial head of  claim 1 , wherein the retaining tabs extend into the horizontal screw head channel when the retaining tabs are in a resting position. 
     
     
         4 . The polyaxial head of  claim 1 , wherein the retaining tabs are separated by a distance that is less than a width of the horizontal screw head channel when the retaining tabs are in a resting position. 
     
     
         5 . The polyaxial head of  claim 1 , wherein the bone screw is slidably retained within the horizontal screw head channel when the bone screw is in the first position. 
     
     
         6 . The polyaxial head of  claim 1 , further comprising a screw neck aperture formed in a bottom face of the polyaxial head, wherein the screw neck aperture terminates at, and is formed continuously with, a bone screw opening formed at the first lateral side of the polyaxial head. 
     
     
         7 . The polyaxial head of  claim 1 , further comprising a rod slot forming a U-shaped channel that is aligned with the vertical screw head channel, wherein the rod slot is configured to receive a fusion rod and guide the fusion rod into a position abutting a bone screw retained within the screw head aperture. 
     
     
         8 . The polyaxial head of  claim 7 , wherein the U-shaped channel defining the rod slot comprises a first channel wall at the first lateral side of the polyaxial head and a second channel wall opposite the first channel wall. 
     
     
         9 . The pedicle implant assembly of  claim 8 , wherein the first channel wall is formed with a first threaded top portion that is discrete from and opposes a second threaded top portion formed on the second channel wall, the first and second threaded top portions being separated by a width of the U-shaped channel. 
     
     
         10 . A polyaxial head comprising:
 a vertical screw head channel formed within a first lateral side of the polyaxial head;   a screw head aperture formed within a second lateral side of the polyaxial head;   a horizontal screw head channel defined by a pair of opposing exterior side walls that connect between the vertical screw head channel and the screw head aperture; and   a pair of retaining tabs formed in the opposing exterior side walls, wherein the pair of retaining tabs are aligned across the horizontal screw head channel and extend into the horizontal screw head channel when the retaining tabs are in a resting position.   
     
     
         11 . The polyaxial head of  claim 10 , further comprising a rod slot formed within the first lateral side of the polyaxial head, wherein a lateral sidewall of the rod slot is formed continuously with a lateral sidewall of the vertical screw head channel and a medial sidewall of the rod slot terminates at the screw head aperture. 
     
     
         12 . The polyaxial head of  claim 10 , wherein the polyaxial head is formed from a single block of material to provide a one-piece construction. 
     
     
         13 . A polyaxial head comprising:
 a vertical channel opening formed in a bottom face of a first lateral side of the polyaxial head;   a screw head aperture formed in a second lateral side of the polyaxial head,   a horizontal screw head channel formed continuously with, and extending away from, the screw head aperture toward the vertical channel opening, and   a rod slot forming a U-shaped channel that is configured to receive a fusion rod, the U-shaped channel comprising a first channel wall at the first lateral side of the polyaxial head and a second channel wall opposite the first channel wall, wherein the first channel wall is formed with a first threaded top portion that is discrete from and opposes a second threaded top portion formed on the second channel wall, the first and second threaded top portions being separated by a width of the U-shaped channel.   
     
     
         14 . The polyaxial head of  claim 13 , further comprising a pair of retaining tabs, wherein the pair of retaining tabs are formed in a wall connecting the horizontal screw head channel and the screw head aperture. 
     
     
         15 . The polyaxial head of  claim 14 , wherein the pair of retaining tabs flex outward from the wall relative to the horizontal screw head channel and the screw head aperture. 
     
     
         16 . The polyaxial head of  claim 14 , wherein the pair of retaining tabs are aligned across the horizontal screw head channel. 
     
     
         17 . The polyaxial head of  claim 14 , wherein the retaining tabs extend into the horizontal screw head channel when the retaining tabs are in a resting position.