| 摘要 |
A polyaxial bone screw assembly (1) includes a threaded shank body (4) having an upper capture structure (8), a head (10) and a multi- piece retainer articulation structure (12). The geometry of the retainer structure pieces (12) corresponds and cooperates with the polyhedral or conical geometry of the capture structure (8) to frictionally envelope the retainer structure (12) between the capture structure (8) and an internal surface (80) defining a cavity (78) of the head (10). The head (10) has a U-shaped cradle defining a channel (66) for receiving a spinal fixation rod (21). The head channel (66) communicates with the cavity (78) and further with a restrictive opening (83) that receives retainer pieces (12) and the capture structure (8) into the head (10) but prevents passage of the frictionally engaged retainer structure (12) and capture structure (8) out of the head (10). The retainer structure (12) includes a substantially spherical surface that mates with the internal surface (80) of the head (10), providing a ball joint, enabling the head (10) to be disposed at an angle relative to the shank body (4). Methods of installation are also provided. |
