Pathological conditions that cause instability of the spine are commonly treated by vertebral fixation involving pedicle screw placement surgery. However, existing methods for preoperative planning are based only on geometrical properties of vertebral structures (i.e. shape) without taking into account their structural properties (i.e. appearance). We propose a novel automated method for computer-assisted preoperative planning of the thoracic pedicle screw size and insertion trajectory. The proposed method extracts geometrical properties of vertebral structures by parametric modeling of vertebral bodies and pedicles in three dimensions (3D), and combines them with structural properties, evaluated through underlying image intensities in computed tomography (CT) images while considering the guidelines for pedicle screw design. The method was evaluated on 81 pedicles, obtained from 3D CT images of 11 patients that were appointed for pedicle screw placement surgery. In terms of mean absolute difference (MAD) and corresponding standard deviation (SD), the resulting high modeling accuracy of 0.39 ± 0.31 mm for 3D vertebral body models and 0.31 ± 0.25 mm for 3D pedicle models created an adequate anatomical frame for 3D pedicle screw models. When comparing the automatically obtained and manually defined plans for pedicle screw placement, a relatively high agreement was observed, with MAD ± SD of 0.4 ± 0.4 mm for the screw diameter, 5.8 ± 4.2 mm for the screw length, 2.0 ± 1.4 mm for the pedicle crossing point and 7.6 ± 5.8º for screw insertion angles. However, a statistically significant increase of 48 ± 26% in the screw fastening strength in favor of the proposed automated method was observed in 99% of the cases.
COBISS.SI-ID: 11250260
Vertebral fixation by pedicle screw placement is the most frequently applied fixation technique in spinal surgery. In this retrospective study we present a comparison of manual and computer-assisted preoperative planning of pedicle screw placement in three-dimensional (3D) computed tomography (CT) images of deformities in the thoracic spine. Manual planning of the pedicle screw size and trajectory was performed by two orthopedic surgeons using a dedicated software for preoperative planning of surgical procedures, while computer-assisted planning was performed by automated image processing and analysis techniques through the optimization of screw fastening strength. The size (diameter and length) and trajectory (pedicle crossing point, inclination in the sagittal plane, inclination in the axial plane) were obtained for 316 pedicle screws from 3D CT images of 17 patients with thoracic spinal deformities. The analysis of pedicle screw parameters, obtained by two manual and one computer-assisted planning, indicated a statistically significant difference in the screw size (p ( 0.05) and trajectory (p ( 0.001). Computer-assisted planning proposed wider (p ( 0.05) and longer (p ( 0.001) screws with a higher (p ( 0.001) normalized fastening strength. The comparison revealed consistency between manual and computer-assisted planning of the pedicle screw size and trajectory, except for the screw inclination in the sagittal plane, as manual planning followed more the straight-forward while computer-assisted planning followed more the anatomical insertion technique. While being faster, more repeatable and more reliable than manual planning, computer-assisted planning was also linked with a higher screw fastening strength and consequently a higher screw pull-out strength.
COBISS.SI-ID: 11678804
Spinal fusion combined with vertebral fixation through pedicle screw placement is the preferred surgical treatment for several spinal deformities. The accuracy of pedicle screw placement is directly related to the surgical outcome, however, manual planning of screw size and trajectory is time-consuming, while automated approaches do not take into account the screw fastening strength. We propose a novel automated method for optimal planning of pedicle screw size and trajectory that takes into account both geometric (i.e. morphometry) and anatomical (i.e. bone mineral density) properties of vertebrae to maximize the screw fastening strength. The size and trajectory of 61 pedicle screws, determined by the automated method in computed tomography images of nine patients, were in high agreement with preoperative manual plans defined by a spine surgeon (mean difference of 0.6 mm in diameter, 4.0 mm in length, 1.7 mm in pedicle crossing, and 6.1º in screw insertion angles), and an increased fastening strength was observed for 50 cases (82%).
COBISS.SI-ID: 11453012