Digital anatomical measurements of safe screw placement at superior border of the arcuate line for acetabular fractures

BACKGROUND Screw penetration into hip joint is a severe complication during acetabular fracture surgery, which might result in osteoarthritis and chondrolysis. The purpose of this study was to obtain the safe and effective screw angles and lengths at acetabular area of the fixation route along the superior border of the arcuate line. METHODS A total of 98 uninjured pelvises of Chinese adults were examined. Each person's computed tomography (CT) scans were reconstructed to create a three-dimensional pelvic model. A curve of the fixation route was delineated and five cross-sections from the pubic tubercle to the sacroiliac joint direction were constructed perpendicularly to the curve. The minimum safe direction, which was tangent to the acetabulum, was measured in the middle three sections and then recorded as the angle α. The maximum effective direction, which was determined by a 14 mm arc and the quadrilateral surface, was also measured in the above sections and then recorded as the angle β. The maximum screw lengths for the five sections were measured. RESULTS The ranges of safe and effective screw insertion angles for the 2nd, 3rd, 4th cross-sections were 21.09±13.57°~40.45±13.60°, 30.43±14.05°~47.54±12.67°, 23.84±11.60°~37.13±8.45°, respectively. The maximum screw lengths for the five sections were 15.89±3.80 mm, 58.83±27.66 mm, 42.94±22.41 mm, 72.43±6.73 mm, 40.99±6.33 mm. The male group showed significantly greater minimum safe angle compared to the female group in the 2nd, 3rd, and 4th sections (p<0.05). CONCLUSIONS The screw insertion at the acetabular area for the female requires greater minimum safe angle towards the quadrilateral surface than the male.