Pelvic inlet and outlet radiographs redefined.

BACKGROUND

Musculoskeletal plain radiographic imaging protocols are typically predicated on orthogonal views of the bone or joint being evaluated. Pelvic injury has been evaluated with 45 degrees inlet and 45 degrees outlet radiographs. While these views are perpendicular to each other, they may not be in the best plane to evaluate pelvic injury because of variable lumbopelvic anatomy. We hypothesized that inlet and outlet radiographic views optimized to examine the clinically relevant osseous landmarks vary substantially from routine 45 degrees inlet and outlet views.

METHODS

Sixty-eight consecutive patients without pelvic ring disruption who had undergone routine axial pelvic computed tomography scans were retrospectively identified. The optimal inlet and outlet angles required to profile the clinically relevant pelvic anatomy were quantified for each patient with use of sagittal computed tomography reconstructions.

RESULTS

The optimal inlet angle to profile the anterior body of S1 required an average caudal tilt of 21 degrees . The average outlet angle (cephalad tilt) perpendicular to the body of S1 was 63 degrees and perpendicular to S2 was 57 degrees . The optimal angles were the same for male and female patients and for patients with normal and dysmorphic pelves and were independent of patient age.

CONCLUSIONS

Screening inlet and screening outlet radiographs made at 25 degrees and 60 degrees , respectively, are recommended to provide accurate profiles of the clinically relevant posterior osseous pelvic anatomy.