Ischial spine sign

Last revised by Joachim Feger on 4 Dec 2021

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 1.

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% 2 even with suboptimal pelvic tilt and or pelvic rotation and specificity of >90% with neutral orientation 1,2.

Limitations

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

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