Abstract:

To study the safe angle and length for screw placement in the posterior wall to avoid intraarticular screw penetration and to provide a theoretical reference for clinical treatment of acetabular fracture.　Methods　A chart review of posterior wall acetabular fractures treated from 2008 to 2016 yielded the study group that met the inclusion criteria. The study group included 15 consecutive patients who had open reduction of posterior wall fracture and internal fixation with plate and screws. Operative and non-operation notes were reviewed and axial view computed tomography scans were analyzed to determine the modified safe angle and length for screw placement in the posterior wall.　Results    All of the above mentioned angles were with respect to the perpendicular of the longitudinal axis of the anterior column without violation of the hip joint away from the acetabular rim，the average width of dangerous zones in the posterior acetabuluar wall was (9.56±1.74)mm in  the operative side and (9.57±1.71) mm in the uninjured side; the average width of safe zones in the posterior acetabuluar wall was (31.67±2.61)mm in the operative side and (31.36±2.75) mm in the uninjured side；the average parallel angle to the cartilage surface of the posterior wall  was (62.33±3.46)° in the operative side and (63.05±3.89)° in the uninjured side, the average length of the screw was （31.67±2.61）mm in the operative side and（31.36±2.75）mm in the uninjured side. There was no statistical difference of data between the posterior wall of acetabulum in the two sides (P>0.05).　Conclusion　1/4 region of the posterior acetabuluar wall close to the acetabular rim is the dangerous zone for screw placement, 3/4 region away from the margin of acetabulum is the safe zone.  The screw angle is 60 degrees to be parallel to the quadrilateral plate, and the length of the screw is 30 mm.

Key words: Axial view computed tomography scans, 　Posterior acetabular fracture, 　Screw, 　Internal fixation