目的　通过三维CT和计算机软件分析以髋臼后壁软骨面平行角为参考时螺钉置入的理想位置、方向和长度，以指导手术和导向器研发。  方法　回顾性分析2008年7月至2016年7月我院收治的不稳定髋臼后壁骨折螺钉、钢板双重固定患者15例,男11例，女4例；年龄21～52岁，平均36.5岁，对比双侧髋臼CT图像评估手术的复位效果，计算机软件统计分析以髋臼后壁软骨面平行角为参考时螺钉置入的理想位置、方向和长度，并区分后壁螺钉置入的相对危险区和相对安全区。   结果　髋臼后壁危险区宽度对照组为（9.56±1.74）mm，手术组为（9.57±1.71） mm，安全区宽度对照组为（31.34±2.73） mm，手术组为（31.53±2.60） mm；髋臼后壁软骨面平行角对照组为（63.05±3.89）°，手术组为（62.33±3.46）°，相对螺钉长度对照组为（31.36±2.75）mm，手术组为（31.67±2.61） mm；上述参数差异均无统计学意义（P>0.05）。  结论　所有病例手术复位效果良好，髋臼后外侧壁靠近髋臼缘侧1/4（约1 cm）范围内为螺钉置入的相对危险区，而位于内侧3/4（约3 cm）范围内为相对安全区域；髋臼后壁软骨面平行角约60°，螺钉相对长度约为3.1 cm，当长度超过3.1 cm左右，角度大于60°，且位于危险区时螺钉进入关节腔风险性增大，而螺钉以小于或等于60°角度在相对安全区内置入可避免螺钉进入关节腔。

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.