Objective To provide the anatomic basis for thelag screw placement in the anterior column of the acetabulum. Methods Twenty-two pelvis specimens with 44 acetabula of the native adult cadavers were studied. The anthropometric measurement was performed on 44 acetabula to determine the shape of the transverse section of the anterior column of the acetabulum, the optimal entry point for the lag screw on the outer table of the ilium, the direction of the screw, and the distance from the entry point to the obturator groove. Results The transverse section of the anterior column of the acetabulum was almost triangle-shaped. The path for the lag screw placement was 10.5±0.8 mm in diameter. The optimal entry point on the posterolateral ilium for the screw fixation was found toexist 9.2±2.4 mm superior to the line between the anterior superior iliac spine and the greater sciatic notch and 38.5±3.8 mm superior to the greater sciatic notch. The distance from the entry point to the obturator groove was 84.1±6.2 mm. The inclination of the lag screw was 54.2±5.5° at the caudal direction in the sagittal plane and 40.7±3.8° in the horizontal plane. The device for the safe screw placement in the anterior column was designed. Conclusion The above datacan facilitate an insertion of one 6.5 mm lag screw into the anterior acetabular column and minimize the risk of articular violation or cortical penetration, which has a narrow margin of safety. The safe length of the lag screw should be 70 mm.The optimal entry point on the posterolateral ilium for the screw fixationis determined to be 10 mm superior to the line between the anterior superior iliac spine and the greater sciatic notch and 40 mm superior to the greater sciatic notch. The inclination of the lag screw should be 55° at the caudal direction in the sagittal plane and 40° in the horizontal plane. It is safe to place thelag screw in the anterior column with the help of the targeting device.
ObjectiveTo compare the biomechanical difference of 4 kinds of internal fixations for acetabular fracture in quadrilateral area. MethodsThe transverse fracture models were created in 16 hemipelves specimens from 8 adult males, and were randomly divided into 4 groups according to different internal fixation methods (n=4): infrapectineal buttress reconstruction plate (group A), infrapectineal buttress locking reconstruction plate (group B), reconstruction plate combined with trans-plate quadrilateral screws (group C), and anterior reconstruction plate-lag screw (group D). Then the horizontal displacement, longitudinal displacement of fractures, and axial stiffness were measured and counted to compare the stability after continuous vertical loading. ResultsUnder the same loading, the horizontal and longitudinal displacements of groups A, B, C, and D were decreased gradually; when the loading reached 1 800 N, the longitudinal displacement of group A was more than 3.00 mm, indicating the failure criterion, while the axial stiffness increased gradually. Under 200 N loading, there was no significant difference (P>0.05) in horizontal displacement, longitudinal displacement, and axial stiffness among 4 groups. When the loading reached 600-1 800 N, significant differences were found in horizontal displacement, longitudinal displacement, and axial stiffness among 4 groups (P<0.05) except the horizontal displacement between groups C and D (P>0.05). ConclusionFor acetabular fracture in the quadrilateral area, anterior reconstruction plate-lag screw for internal fixation has highest stability, followed by reconstruction plate combined with trans-plate quadrilateral screws, and they are better than infrapectineal buttress reconstruction plate and infrapectineal buttress locking reconstruction plate.