Polyaxial locking assembly

Abstract

A locking mechanism for a polyaxial locking screw is provided, together with a polyaxial locking assembly for locking a receiving member to a substrate. Also provided is a plating system for pelvic reconstruction.

The invention claimed is: 
     
       1. A polyaxial locking assembly, comprising:
 a receiving member comprising at least one open cavity having a generally spherical inner surface; 
 a one-piece bushing with a generally spherical outer surface sized and shaped to fit within the cavity, said the outer surface engaging the inner surface of the at least one open cavity, and the bushing comprising a hole aligned with an axis of the bushing, said the hole further provided with a female thread threads; 
 a screw provided with a male thread threads for engagement, in use, with the female threads of the bushingand the hole and thread thereof;, wherein the at least one open cavity is provided with at least one radially outwardly protruding cavity keyway; 
 wherein the bushing further comprisingcomprises a bushing groove aligned with aan outer perimeter of the bushing, saidthe outer perimeter being on a plane substantially orthogonal to the bushing axis, the bushing groove being shaped so that the bushing, at aan inner perimeter of the bushing groove and on saidthe plane, providesdefines a cam, said cam having at least one lobe; 
 there is further provided an anti-rotation member that, in use, is positioned within the bushing groove between the cam and an inner surface of the cavity, the anti-rotation member further comprising a key for cooperative engagement with the cavity keyway such that the ability of the anti-rotation member to rotate within the cavity is restrained; 
 wherein the anti-rotation member further having a generally annular, open or closed geometry and having a radial thickness, and further being contoured such that at least one portion of the anti-rotation member has an effective radial thickness greater than that of at least one other portion; and  
 such thatwherein in use, the screw may be threaded into the bushing until it reaches a limit of travel, whereupon further rotation of the screw also rotates the bushing, forcing the effectively radially thicker portion of the anti-rotation member outwards so that the anti-rotation member engages with the inner surface of the cavity and causes a build up of friction between the cam, the anti-rotation member and the inner surface of the cavity, so as to lock the assembly in a desired orientation. 
 
     
     
       2. The polyaxial locking assembly of claim 1, wherein the anti-rotation member is closed and substantially circular.  
     
     
       3. The polyaxial locking assembly of claim 1, wherein the anti-rotation member is open and generally c-shaped.  
     
     
       4. The polyaxial locking assembly of claim 1, wherein the hole of the bushing is a blind hole.  
     
     
       5. A polyaxial locking assembly, comprising:
 a receiving member comprising a cavity having an inner surface with a generally spherical profile with at least one outwardly-protruding keyway;   a one-piece bushing having an outer profile, wherein a portion of which has a generally spherical outer surface configured to fit within the cavity, wherein the outer surface engages the inner surface of the cavity, the bushing further comprising a threaded hole defining a bushing axis and a perimeter groove located on a plane substantially orthogonal to the bushing axis, the perimeter groove having at least one outwardly-extending protrusion; and   an anti-rotation member configured to be positioned within the bushing groove, the anti-rotation member having a key for engagement within the keyway, wherein the anti-rotation member has a first radial thickness and a portion with a second radial thickness effectively greater than that of the first radial thickness.    
     
     
       6. The polyaxial locking assembly of claim 5, further comprising a screw adapted for operative engagement with threads of the threaded hole of the bushing, wherein rotation of the screw beyond a predetermined amount rotates the bushing which urges the portion of the anti-rotation member with the second radial thickness against the inner surface of the cavity.  
     
     
       7. The polyaxial locking assembly of claim 5, wherein the anti-rotation member is closed and substantially circular.  
     
     
       8. The polyaxial locking assembly of claim 5, wherein the anti-rotation member is open and generally c-shaped.  
     
     
       9. The polyaxial locking assembly of claim 5, wherein the hole of the bushing is a blind hole.  
     
     
       10. The polyaxial locking assembly of claim 5, wherein the perimeter groove does not extend the entire perimeter of the bushing.  
     
     
       11. The polyaxial locking assembly of claim 5, wherein the cavity of the receiving member is a first cavity, and further comprising a second cavity configured to accept a second bushing comprising a threaded hole that defines a second bushing axis.  
     
     
       12. The polyaxial locking assembly of claim 11, wherein the bushing axis of the first cavity and the second bushing axis are parallel.  
     
     
       13. The polyaxial locking assembly of claim 11, wherein the bushing axis of the first cavity and the second bushing axis are not parallel.  
     
     
       14. The polyaxial locking assembly of claim 5, wherein the cavity has a first beveled end associated with a first surface of the receiving member and a second beveled end associated with a second surface of the receiving member.  
     
     
       15. The polyaxial locking assembly of claim 5, wherein the receiving member has tapered first and second ends.  
     
     
       16. A polyaxial locking assembly, comprising:
 a receiving member comprising a hole extending therethrough with a generally cylindrical inner surface having at least one outwardly-extending portion with an outer dimension greater than a radius of the at least one hole;   a one-piece bushing configured to fit within the hole and having an outer profile complementary to the inner surface of the hole, wherein the outer surface engages the inner surface of the hole, the bushing having a threaded hole defining a bushing axis, and wherein the outer profile comprises a perimeter groove located on a plane substantially orthogonal to the bushing axis, the perimeter groove having at least one outwardly-extending protrusion; and   an anti-rotation member configured to be positioned within the bushing groove, the anti-rotation member further comprising an outwardly-extending finger for engagement within the outwardly-extending portion of the hole, the anti-rotation member having a first radial thickness and at least one portion with a second radial thickness that is effectively greater than that of the first radial thickness.    
     
     
       17. The polyaxial locking assembly of claim 16, further comprising a screw adapted for operative engagement with the threaded hole of the bushing, wherein rotation of the screw beyond a predetermined amount rotates the bushing to urge the at least one portion with a second radial thickness against the inner surface at least one hole.  
     
     
       18. The polyaxial locking assembly of claim 16, wherein the anti-rotation member is open and generally c-shaped.  
     
     
       19. The polyaxial locking assembly of claim 1, wherein the bushing is a unitary structure.  
     
     
       20. The polyaxial locking assembly of claim 16, wherein the bushing is a unitary structure.