The pelvic tear-figure: a three-dimensional analysis of the anatomy and effects of rotation.

Abstract

Fluoroscopy and three-dimensional CT analysis were used to define the contributing anatomy and changes in appearance of the tear-figure with rotation of a pelvis. The tear-figure is a cortical structure of iliac and ischial bone that appears on anteroposterior (AP) roentgenograms of the pelvis. The contribution of these cortices to the pelvic tear-figure changes with rotation of a pelvis in a radiographic field. Cortices contributing to the tear-figure are not continuous throughout. The lateral border, inferior margin, and inferior one third of the medial border of the tear-figure is formed by a continuous segment of cortical bone extending from the deepest portion of the acetabulum around the cylindric acetabular notch, and along the inferior medial wall of the ischium. The superior two thirds of the medial border of the tear-figure consists of cortical bone extending superiorly along the medial wall of the ilium, which is not in continuity with the remainder of the components of the tear-figure. The tear-figure is not a structure of constant radiographic dimension. Its apparent dimensions change with rotation of the pelvis. The positioning of the patient for the AP pelvic roentgenogram is thus important when studying the effects of acetabular pathology on the appearance of the pelvic tear-figure.