Screw fixation is the most appropriate from a mechanical point of view. During tests, however, screw fixation falls short of its promises. This leads to the hypothesis that in most cases screws pull out because the bony anchoring of the pedicle screwing fails. Screws are less effective if their anchoring in the pedicles cannot be guaranteed, which is probably the reason for their relative weakness. Screw diameter should be chosen according to the size of each pedicle. The findings showed that hooks impose additional stresses on the vertebrae.

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