| 摘要 |
A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a receiver and a retainer having spherical inner and outer surfaces. The retainer is compressible, having an opening with two ends that may be pressed toward one another. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod. The receiver channel communicates with a cavity partially defined by a spherical surface and having a restrictive opening that allows for loading the capture structure and the compressed retainer into the receiver, but prevents passage of the retainer/capture structure assembly out of the receiver. The retainer is simultaneously bottom loaded with the shank capture structure by compressing open ends of the retainer towards each other and about a neck of the bone screw shank, the retainer resiliently springing back into a rounded shape after insertion in the receiver. The retainer spherical surfaces slidingly mate with both the receiver and the capture structure, providing multiple or compound polyaxial articulation.
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