Defining safe zones for the infra-acetabular screw: A gender-specific CT morphometric study in the South Asian...

Acetabular fractures are among the most complex orthopaedic injuries, requiring precise anatomical reduction and stable fixation. Infra-acetabular screw (IAS) enhances fixation strength by closing the periacetabular frame. This study aims to determine entry points and corridor parameters for IAS placement in the South Asian population, identify gender-specific differences, and evaluate its practical usability in managing acetabular fractures.

CT scans of 200 hemipelves (100 pelvises) were analysed using RadiAnt DICOM Viewer. Exclusion criteria included patients under 18 years of age, prior pelvic fractures, or bony pathologies. An all-intraosseous screw trajectory was defined. Parameters measured included entry point distances, corridor length, diameter, and angles in the axial and sagittal planes. Gender-specific differences were statistically analysed.

Significant gender differences were noted in entry point distances (from the pubic symphysis, anterior wall, and medial wall), corridor length, and axial-plane angle. Females required more lateral angulation for screw placement. Only 13 percent of the hemipelves in our study had a corridor diameter ≥5 mm, which differs from studies conducted on Western populations. The mean minimum diameter was narrower compared to Western populations, indicating that a 3.5 mm screw is optimal for the South Asian population.

This study provides comprehensive dimensions for IAS placement, highlighting gender-specific planning requirements. These findings enhance preoperative planning and patient-specific treatment strategies for complex acetabular fractures.