Feasibility Of Screw Placement Research Articles

Feasibility of screw placement on posterior occipital condyle assisted by occipital tangent angulation

Objective: To investigate the practicability of occipital tangent angle in assisting posterior occipital condylar screw placement and to verify the safety and accuracy of self-made screw placement device for auxiliary screw. Methods: Occipito-cervical region specimens of 12 adult corpses were selected and scanned by thin-cut CT examination.The three-dimensional reconstruction of occipital and atlas was simulated for each specimen, and 3-matic software was used to measure the setting parameters, including occipital tangent angle, head obliquity, internal inclination angle, length of the screw and the distance from the inferior margin of hypoglossal canal to the screw axis.Using the self-designed occipital condylar screw placement device, combined with occipital tangent angle, internal inclination angle and insertion point, the posterior occipital condylar screw specimen was inserted with nails with assisting tool.The occipito-cervical region was reconstructed and scanned by thin-cut CT examination again after the operation to measuring the parameters of screw placement after actual screwing.The paired t test was used to compare the parameters of screw placement before and after operation. Results: Pre-operative three dimensional reconstruction of occipital condyle screw showed that the head obliquity was 5.3°±0.9°, the tangent angle was 14.9°±3.7°, the internal inclination angle was 28.1°±5.9°, and the length of screw insertion was (21.4±1.7) mm respectively; the distance from the inferior margin of hypoglossal canal to the screw axis was (4.74±0.36) mm.There was no significant difference in the parameters of analogue nailing between the left and right occipital condyles before the operation (t=-1.32, -0.48, 0.10, 0.23, 0.09, all P>0.05). The occipital condylar screw was safely implanted with screw placement device.The screw was located in the ideal nail insertion channel after operation by CT scan evaluation, without any injury to the hypoglossal canal, the atlanto-occipital articular surface and other structure.After the operation, the actual nailing parameters were measured: the head inclination angle was 5.2°±0.7°, the tangent angle was 15.1°±3.2°, the internal inclination angle was 28.2°±4.2°, the length of screw insertion was (21.5±1.7) mm, the distance from the inferior margin of hypoglossal canal to the screw axis was (4.54±0.29) mm.There was no significant difference between the left and right side in the actual screw placement parameters (t=-0.77, 0.82, 0.56, 0.22, 0.21, all P>0.05). It was found that there was no significant differences in the head obliquity, the occipital tangent angle, the internal inclination angle, length of screw entry, and the distance from the inferior margin of hypoglossal canal to the screw axis before and after the operation (t=0.56, -0.47, -0.18, -0.70, 1.89, all P>0.05). Conclusion: The occipital tangent angle can be measured directly in the process of posterior occipital condyle screw insertion to guide occipital condylar screw insertion, and the self-made occipital condylar screw placement device can effectively combine the three parameters: occipital tangent angle, head inclination angle and insertion point, which can improve the safety of posterior occipital condylar screw insertion.

Anatomic Parameters

Analysis via computed tomography imaging software. To determine parameters for ideal intralaminar screw trajectory and the feasibility of screw placement at L3, L4, and L5 laminae for pars defect fixation. To our knowledge, no studies provide anatomic parameters for ideal intralaminar screw trajectory for treating spondylolysis. We used advanced imaging software for 3-dimensional interactive viewing to analyze 20 randomly selected normal adolescent lumbar computed tomographic scans. The ideal intralaminar screw trajectory was drawn from the inferior lamina, a point chosen to maximize cortical diameter at the isthmus of the lamina and bisect the pedicle. We measured and evaluated ideal trajectory parameters for percutaneous screw placement for pars defect fixation at the L3 to L5 laminae. The ideal pathway was the thick portion of the lamina between the inferior edge of the lamina and the pedicle. This area was close to the inferior articular process (axial plane), becoming more so at progressively caudal levels. At the ideal trajectory, the mean (standard deviation) coronal angle slightly decreased (L3-L5): 7.3° (5.1°), 6.6° (3.7°), and 4.2° (2.5°), respectively. The trajectory distance increased from cranial to caudal. These parameters increased (L3-L5): mean distance (transverse plane) between the starting point and middle of the spinous process, 1.2 (0.18 cm), 1.3 (0.2 cm), and 1.6 (0.3 cm), respectively; mean screw sagittal angle with respect to the posterior skin, 15.5° (5.0°), 24.3° (6.5°), and 43° (5.8°), respectively; and mean distance for guide wire entry, 28.8 (10.6 cm), 20.1 (5.4 cm), and 11.9 (2.1 cm), respectively. At the ideal screw trajectory, pars fixation by intralaminar screw is uniformly feasible at L3 to L5 laminae, where most patients can accommodate a 4.5-mm screw. 2.

Feasibility of Screw Placement in the Occipital Condyle of Chinese Patients for Occipitocervical Arthrodesis: A Cadaveric Study.

The feasibility of computed tomography (CT) and two-dimensional (2D) reconstruction-guided screw placement in the occipital condyle (OC) of Chinese patients was investigated. Twenty (40 OCs) fresh cadaveric specimens with intact superior cervical spine and occipital bones were placed in the prone position. Simulated screw placement was achieved by placing 4.0 mm diameter virtual screws with the help of the 2D reconstruction CT scan image technology. Maximal screw length, angulation in the sagittal and transverse planes, and medial and cranial base OC entry points were determined and recorded. Actual screw placement was achieved by similar placement; actual position and angulation were determined by postoperative CT scanning. Screws were successfully inserted in 36 of 40 (90%) OCs. Four ruptures of the medial OC wall were on the left side. Actual screw placement did not damage the hypoglossal canal, and no screws pierced the medial or lateral OC walls. Females displayed significantly smaller left and right maximum screw lengths than males (p < 0.05); no other significant gender differences were noted. The results can feasibly accommodate 4-mm OC screws for OA treatment. As in other populations, OC shape and size is smaller in females and varies in Chinese individuals, necessitating individualized imaging for good outcomes.