| 摘要 |
PROBLEM TO BE SOLVED: To provide polyaxial bone screws for use in bone surgery, particularly spinal surgery. SOLUTION: The polyaxial bone screw includes a threaded shank 4 body having an upper capture structure 8, a head 10, and a multi-piece retainer articulation structure 12. The geometry of the retainer structure corresponds and cooperates with the polyhedral or conical geometry of the capture structure to frictionally envelope the retainer structure between the capture structure and an internal surface defining a cavity 78 of the head. The head has a U-shaped cradle defining a channel 66 for receiving a spinal fixation rod. The head channel communicates with the cavity and further with a restrictive opening that receives the retainer structure and the capture structure into the head and prevents passage of the frictionally engaged retainer structure and capture structure out of the head. The retainer structure includes a substantially spherical surface that mates with the internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body. COPYRIGHT: (C)2011,JPO&INPIT
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