Computerized tomographic evaluation of acetabular anatomy.

In this study, accurate identification of the location of the acetabular teardrop and ilioischial line on the cadaveric pelvis was attempted using computerized tomographic (CT) scanning and conventional roentgenographic techniques. The acetabular teardrops and ilioischial lines of four whole pelvic anatomic specimens were outlined with barium impregnated latex strings utilizing conventional roentgenograms, fluoroscopy, and stereoscopic control. Computed tomographic scanning was then performed, and axial and coronal CT reformations were created. Roentgenograms, CT scans, and magnetic resonance images of the pelves of ten patients with avascular necrosis of the femoral head were also reviewed to correlate the cadaveric study with specific clinical cases. The acetabular teardrop is a U-shaped figure on roentgenograms taken in a neutral anteroposterior projection. It is a complex geometric structure found to be in a constant position in the anteroinferior aspect of the acetabular wall. Its appearance changes with rotation of the pelvis or incident beam, as the teardrop represents a two-dimensional image of the tangents of a series of curves of varying radii. The ilioischial line is located posterior to the acetabulum and corresponds to tangents on the cortex of the posterior column. Computed tomography imaging with reconstruction identifies acetabular anatomy most clearly and allows precise measurements to be made.