| Background: For displaced acetabular fractures, surgical treatment should be adopted.Lag screw technology plays a good role in interfragmentary compression to get a better reduction, which is widely accepted and recommended. At the same time,only using a single anterior approach to fix acetabular fracture of anterior and posterior also reduced the operation trauma.However, the proper placement of antegrade lag screw in posterior column is still facing great challenges. Technically, due to the irregularities of anatomic structure of the posterior column, specific quantitative anatomical information is inadequate, so there are risks of cutting the bone cortex, impairing the articular surface and the important acetabular blood vessels and nerves in lag screws and that’s why the antegrade lag screw technique is not commonly used in posterior column.Objective: This study aims to use mimics 10.01 software to simulate the insertion of anterograde lag screw in the acetabular posterior column by pelvic dimensional models,trying to find a safety zone for the placement of screws located on the iliac plate and then its related anatomical parameters are measured to provide a theoretical basis for the clinical implementation of anterograde lag screw’s anterior approach to the posterior column technique, as well as an applied anatomy basis for future research and development of the safety zone guides of screw placement.Methods: 40 cases of the original 64-slice CT DICOM data with the scanning scope covering the pelvis are collected randomly with 20 men and 20 women. 40 cases of original DICOM data obtained are imported to MIMICS 10.01 software successivelyfor three-dimensional modeling. The center point O of the intersection level between the lower edge of the axial obturator and ischial tuberosity is artificially defined as the piercing point of the lag screw and the bony cortex of the iliac plate in the transverse level is differentiated and the anchor point of the lag screw is defined. The position parameters of anchor and piercing points are imported to Med CAD module to build virtual lag screws. All the lag screws with its screw threads located in the bone of acetabular posterior column are filtered out, which are the ones located in the safety zone, for its anchor point lies in the area on the bony cortex of the iliac plate, which is the safety zone for the placement of lag screw in acetabular posterior column. The length of each lag screw and their placement angles are measured to obtain the length and angle range for lag screw placement. Besides the distance from the anchor point to the anterior superior iliac spine, anterior inferior iliac spine and auricular surface front are measured to get the anatomical parameters related to the security zone of screw placement.Results: After the measurement, it is fount that all the anchor points of lag screws in virtual acetabular posterior column that meet the filter criteria have formed a placement safety area in a triangle shape on the boney cortex of the iliac plate. The distances of the triangle’s three vertices A, B, C to the anterior superior iliac spine are 66.7±2.9mm(61.0-72.6mm), 79.9±6.0mm(71.3-93.9mm), 58.3±4.8mm(50.1- 66.9mm) respectively;the distances to the anterior inferior iliac spine are 47.4±2.8mm(42.0-52.6mm),74.7±7.5mm(62.2-87.8mm), 63.6±6.5mm(51.2-74.5mm); the distances to the auricular surface front are 32.8±5.3mm(23.4-42.5mm), 28.8±5.6mm(20.1-41.0mm),50.9±5.5mm(41.5-59.5mm) respectively. Screw OA is the shortest one inside the safety zone with the length of 99.5±4.6mm(87.6-108mm), and screw OC is the longest one with the length of 133.6±12.3mm(120.0-148.7mm). All the virtual screws within the safety zone in the acetabular posterior column are in a forward state of abduction, with the range of abduction angles of 10.4 ± 2.9 °(4.4-15.9 °) and the forward angles’ range of 12.0 ± 2.6 °(7.2-17.4 °). The differences between men and women in the screw length at three vertices, the insertion angle of screw OA with the coronal and sagittalplane, the angle between the screw OB and the sagittal plane, the angle of screw OC with coronal and sagittal plane, the distances of point B to anterior superior iliac spine and anterior inferior iliac spine, the distances of point C to the anterior inferior iliac spine and the auricular surface front and the safety angular range of screws in anteroposterior and lateral positions are all statistically significant(P <0.05), while there are no statistical differences in the insertion angle between the screw OB and coronal plane, the differences of point A to the anterior superior iliac spine, anterior inferior iliac spine and auricular surface front, the distance of point B to the auricular surface front and the distance of point C to the anterior superior iliac spine and so on(P> 0.05).Conclusion: By using MIMICS 10.01 software to simulate the placement of antegrade lag screws in acetabular posterior column, a safety area for the placement of screws in a triangle shape on the iliac plate is indeed found out. All screws within the area are located in the bone of acetabular posterior column with the piercing points all pointing to the midpoint of the intersection level between the lower edge of the obturator and ischial tuberosity. However, due to the complex anatomy of the acetabular posterior column, it still remains to be a difficult task for the orthopedic surgeon to directly apply the research results into the clinical practice of antegrade lag screw placement in posterior column, but the safety zone guides developed in the future might make the operation process easy and safe. |
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