摘要：

A device for supporting a spinal column includes a screw having a U- shaped head, a joining element received within the head, a threaded bolt received within and threadedly engaging the head, and a cap covering an upper portion of the head. The head is internally threaded. The threaded bolt engages the joining element to block relative movement between the joining element and the screw. The cap avoids spreading of the head upon tightening of the bolt in the head.

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