Does increased acetabular depth affect safe infra-acetabular screw placement in acetabular fracture fixation?

BACKGROUND Infra-acetabular screws enhance the fixation strength in acetabular fractures with separation of both columns. Placement without iatrogenic femoral head violation is challenging. PURPOSE To assess the impact of the acetabular configuration, the patients' age and gender on safe infra-acetabulum screw insertion. METHODS In 112 patients (69 females; mean age: 34 years, range 17-88; n = 200 hips), the lateral center-edge angle (LCE) was measured on radiographs. Using corresponding axial CT scans the residual distance from (the lateral border) of the screw to (the medial border of) the femoral head ("Screw-to-Femoral Head distance"; "RD_SFH") was determined. Statistical analysis was carried out using linear regression, multiple linear regression and normal distribution estimation. RESULTS The mean (range) LCE angle was 30° (7°-51°) and the mean (range) "RD_SFH" was 5 mm (1-14 mm). The linear regression model shows a significant linear relation between LCE and "RD_SFH" with a slope parameter of - 0.15 (p value < 0.0001), the Pearson correlation between LCE and "RD_SFH" is - 0.56 (CI [- 0.71, [- 0.40]). Age did not have a significant impact on the relation between LCE and "RD_SFH" (p value 0.85). Compared to male patients, in females, the intercept is 4.62 mm (p value 0.0005) less, the slope parameter is 0.09 (p value 0.029) larger. CONCLUSION The virtual possibility to place an infra-acetabular screw was given in all patients. An increasing depth of the acetabulum correlated with a decrease in residual distances. As hip joint cartilage thickness was not considered in measurements, intraoperative rule-out of screw mispositioning especially in deep acetabular sockets and females is still of utmost importance