| 摘要 |
A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head, a retaining ring and a nut. The external capture structure surface includes a threaded portion and a smooth portion; the smooth portion for slidably mating with the retaining ring and the threaded portion for rotatable attachment to the nut within a cavity of the head. The head has a U-shaped cradle defining a channel for receiving a spinal fixation rod. The head channel communicates with the cavity and further with a restrictive opening that allows for loading the capture structure into the head but prevents passage of the retaining ring out of the head. The retaining ring has an external substantially spherical surface that mates with an internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body. The nut fixes the retaining ring to the shank and also provides a tool engagement formation for driving the shank body into bone. The nut further includes a weakened area, providing for deformation and interlocking of threaded portions of the capture structure and the nut.
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