Digital anatomical parameters of retrograde screw placement for superior pubic ramus fractures

Objective To obtain the optimal channel parameters of the retrograde screw with subpubic symphysis joint as optimal entry point through 3D pelvic model reconstruction and virtual optimal insertion, so as to provide a theoretical basis for the clinical safety screw fixation for superior pubic ramus fractures. Methods CT images of 50 patients with non-pelvic fracture from Chinese PLA General Hospital from July 2016 to September 2017 were randomly collected and imported into MIMICS software to reconstruct pelvic 3D models. Digital screws were used to simulate insertion from the pubic symphysis. The diameter and length of the screw were measured, as well as the angle between the screw axis and three planes. Results The average diameter of the narrowest zone was (7.54±1.02) mm in male and (6.23±1.61) mm in female. For φ4.5 mm digital screw, the angle between the screw track and sagittal plane, coronal plane and transverse palne were (51.10±3.26)°, (8.24±1.33)°, (39.47±2.58)° in male, and(53.44±3.78)°, (8.45±2.15)°, (35.26±4.76)° in female, respectively. Conclusion Based on Nakatani fracture classification, when the suprapubic fracture occurs in zoneⅠ, the entry point can be selected in the subpubic symphysis to achieve adequate screw track length to fix fracture.