Theoretically the use of a drill removes the bone tissue while the use of a probe promotes the compacting of the bone on the wall of the pilot hole. This compacting of the bone on the walls of the pilot hole could improve the quality Pacritinib phase 3 of the implant fixation. The diameter of the pilot hole in relation to the internal diameter of the screw has not been appreciated in this stage of the procedure, although its influence has been observed in mechanical tests.14,15 The aim of the study was to evaluate the possible influence of the diameter and of the method of preparation of the pilot hole on the insertion torque and on the pullout resistance of pedicle screws with conical internal diameter, using swine vertebrae.

MATERIAL AND METHODS The study was carried out on 280 lumbar vertebral pedicles (L1-L6) of pigs of the Landrace breed, with age averaging 90 days and approximate mass of 80kg. The vertebrae were stored at a temperature of -20��C. Prior to the performance of the trials, the vertebrae were removed from the freezer and kept for 12 hours at a temperature of 5��C in the refrigerator, then subsequently for two hours at room temperature in order to reach thermal equilibrium and not alter the physical properties of the bone. The bone mineral density of the vertebrae was evaluated by means of dual-energy x-ray absorptiometry (DEXA?), using the QDR system with version 11 – 2:5 software (Hologic 4500 W?, Walthan, MA, USA), observing the mean value of 16.33 �� 1.90 g/cm3. We used pedicle screws with conical internal diameter and external diameter of 4.2mm and 5.

2mm, belonging to the USSII vertebral fixation system (Universal Spine System-Synthes?). The first with a thread length of 30mm and conical internal diameter, with greater internal diameter of 3.8mm and lesser of 2.2mm, and the second with 35mm of thread length and conical internal diameter, with greater internal diameter of 4.2mm and lesser of 2.5mm. (Figure 1) Figure 1 Screws used in the study. (A) 4.2mm x 30mm screw. (B) 5.2mm x 35mm screw. The hole for insertion of the implant was prepared using a drill, sharp probe and steel pointed probe, with diameters of 1.6mm, 2.2mm, 2.5mm, 2.8mm, 3.4mm, 3.8mm and 4.2mm, used according to the experimental group. (Figure 2) Figure 2 Instruments used to make the pilot hole. Drill (A); Pointed probe (B) and Sharp probe (C).

The drilling depth of the pilot hole Anacetrapib was defined with a basis on the thread length of the screw. The perforations with the probes were executed manually while the perforations with the drills were executed with a bench drill at a speed of 455 rpm. The screws were inserted in the vertebral pedicles from the posterior portion of the vertebral arch using anatomical references of the upper articular surface and transverse process. The screw insertion torque was measured with a Mackena? MK-201 digital torquemeter with a capacity of 10 N.m and precision of 0.01 N.