OBJECTIVE: To determine the effect of pilot hole tapping, together with other variables such as pilot hole diameter, in relation to inner screw diameter and preparation mode, on the insertional torque and pullout strength of the screws used for anterior fixation of the cervical spine. METHODS: Twenty polyurethane test bodies and 30 thoracic vertebrae (T1-T5) were tested. Four holes were drilled into each test body, two of them with a diameter of 2.0 mm and two with a diameter of 2.5 mm. The holes were drilled with a bit or probe according to the experimental group. Pilot hole tapping was or was not done, dividing the experimental group into equal subgroups. Eight experimental groups were formed, four of which used polyurethane specimens and four used sheep vertebrae. Cortical screws 3.5 mm in outer diameter and 14 mm long were inserted into the pilot holes. Insertional torque was measured during screw implantation and mechanical assays were then performed using an Emic® universal testing machine. Tesc 3.13 software was used for data analysis. Load cells with a capacity of 1000 N, were used and the rate of force application was 0.2mm/min. The mechanical property evaluated was the maximum pullout force of the screws. RESULTS AND CONCLUSIONS: Pilot hole tapping significantly decreased insertional torque and pullout force in all experimental groups.
Spine; Bone screws; Biomechanics; Torque; Orthopedic fixation devices
