Ischial spine sign

The ischial spine sign is a radiographic sign on the AP view of the pelvis, for the diagnosis of acetabular retroversion, which poses a form of pincer morphology and predisposes to femoroacetabular impingement.

Acetabular retroversion seems to be a result of a rotation of the entire acetabular complex including the ischial spine .

Radiographic features

The triangular projection of the ischial spine is visible medially to the pelvic inlet or iliopectineal line. The sign is supposed to have a sensitivity and specificity of 90% and 71% even with suboptimal pelvic tilt and or pelvic rotation and specificity of >90% with neutral orientation .

Limitations

Visibility of the ischial spine increases with pelvic tilt and ipsilateral pelvic rotation.