Mechanical assays were performed in order to assess the influence of pilot hole diameter versus screw's inner diameter on screw pullout resistance in the vertebral fixation systems applied to the vertebral body. The study was conducted in two stages. In the first, polyurethane test bodies were used for placing 5 and 6 mm screws, and, in the second stage, the screws were inserted into the lateral surface of the lumbar vertebral bodies of pigs. The pilot hole was built with drills with smaller, similar or larger diameter than screws' inner diameter. Mechanical pullout assays were performed using a universal test machine for the assessment of maximum pullout screw resistance. The diameter of the pilot hole versus screw's inner diameter was shown to influence screw pullout resistance.
Spine; Bone screw; Biomechanics
