OBJECTIVE: To evaluate the effect of the pilot hole preparation technique using a blunt probe, a sharp probe and a drill on pullout strength of vertebral screws. METHODS: Screws of the USS vertebral fixation system measuring 5, 6 and 7 mm in outer diameter were used. The screws were implanted into bovine bone samples in which pilot holes were prepared with blunt probes, sharp probes and drills. The diameter of the pilot hole was smaller, equal to or wider than the inner diameter of the screw. Three holes of the same diameter were made in the same bone sample by the three preparation techniques. The screws were inserted and pullout mechanical tests were performed using an Emic® universal testing machine, Tesc 3.13 software, a 2000 N load cell, a 2 mm/min rate of force application, a 5 N preload and a 10 second time of accommodation. The property assessed in the mechanical tests was maximum pullout strength. RESULTS: The pilot hole preparation technique and the hole diameter in relation to inner screw diameter affected the pullout strength of 5 and 6 mm screws, which was greater for screws inserted into pilot holes prepared with a probe. No significant difference between preparation techniques of pilot hole was observed for 7 mm screws. CONCLUSION: The technique of pilot hole preparation influenced the pullout strength of 5 and 6 mm screws. No difference was observed for 7 mm screws.
Spine; Bone screws; Biomechanics
