Abstract:Objective To study the position of the lower acetabular screw in the three-dimensional model of Chinese pelvis.Methods Subjects requiring pelvic CT scan due to non-pelvic diseases from 2013 to 2018 were selected.22 males (44 hips) with a mean age of (33.5±5.1)years and 33 females (66 hips) with a mean age of (35.1±5.6)years were selected.Lower part of acetabulum cortex and medullary cavity were markedin 3D reconstructed images.A cylinder which was most fittable of the medullary cavity was automatically generated.The cylinder represented the narrowest part the screw need to pass.The cylinder was extendedand passed through the cortex of pelvic entrance,the point where the cylinder axis pass through the pelvic cortex represented the screw entrance point and the position of this point was measured,the cylinder axis was used to measure the angle and length of screw path.The entrance plane,coronal and sagittal plane of the pelvis were marked.The length of the nail path inside the cortex was measured.The distance from the anterior superior iliac spine to the symphysis pubis (A) and the distance from the symphysis pubis to the entrance of the screw path (B) were measured,and the ratio of A/B was calculated.The angle between the screw path and the sagittal plane on the pelvic entrance plane,the angle between the screw path and the pelvic entrance plane on the sagittal plane,the angle between the screw path and the sagittal plane on the coronal plane,and the angle between the screw path and the coronal plane on the sagittal plane were measured.The difference between male and female was compared,and P<0.05 was considered as statistically significant.Results 27% of male subjects and 36% of female subjects did not exist.The length of the screw path was (89.0±10.1)mm for men and (83.6±8.7)mm for women,and the difference was statistically significant (P<0.05).The diameter of screw path was (4.3±1.0)mm in male and (3.4±0.8)mm in female,the difference was statistically significant (P<0.05).The angle between the screw path and the sagittal plane on the entrance plane of the pelvis was (5.1±2.1)°in male,and (18.0±7.6)°in female,the difference was statistically significant (P<0.05).The angle between the screw path and the pelvic entrance plane on sagittal plane was (75.5±12.5)° in male and (70.6±11.5)° in female,and there was no significant difference(P>0.05).The angle between screw path and sagittal plane on coronal plane was (11.0±6.1)° in male and (18.1±10.1)° in female,and the difference was statistically significant (P<0.05).The angle between the screw path and the coronal plane on sagittal plane was (60.0±13.8) ° in male and (57.1±12.9)° in female,and there was no significant difference(P>0.05).The ratio of A/B was (2.5±0.3) in male and (2.6±0.3) in female,the difference was on statistically significant (P>0.05).Conclusion Inferior acetabular screw path is more likely to exist in male.The length and diameter of screw path in male are larger than that in female.The angle between the screw path and the sagittal plane on the entrance plane and the coronal plane in male is smaller than that in female.The finding suggests that the screw pathis more parallel to the sagittal plane.Compared with Westerners,the percentage of Chinese with existence of screw path is smaller,the diameter of the screw path is smaller and the length of the screw path is longer.The screw path of Chinese is closer to the pubic symphysis,while the screw path of Westerners is more parallel to the sagittal plane.
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