[Anchoring experiments on human cadaver vertebrae using various types of screws]

The firmness of the bone structure of vertebrae of human cadavers was investigated by turning screws of four different types into vertebrae T6 to L5 and subjecting them to axial tension up to the point of extraction. It was found that the cancellous bone screws (rather than the Zielke screw) had the best anchoring characteristics in bone tissue. The shearing fracture stress of the vertebral bone tissue was found to be approx. 1.80 N/mm2; the relation between the extraction forces and the individual vertebrae was also examined. In addition, the extraction forces were determined for screws inserted into vertebrae T6 to L4, as performed in Zielke's ventral spondylodesis procedure, as well as the lower tolerance limit for each vertebra in this segment of the vertebral column.