Precise identification of radiographic acetabular landmarks.

Accurate radiographic demonstration of pelvic anatomical landmarks is predicated on proper positioning of the patient. Interpretation of acetabular abnormality especially may be difficult when to the artifact created by pelvic asymmetrical positioning there is added true femoral head displacement. A radiograph of hip joint abnormalities in a child with congenital hip dislocation where positional distortion was present served to illustrate the problem. To clarify the direction and magnitude of acetabluar alterations with specific pelvic positions, radiographs and photographs were taken of anatomic models outlined by suitably placed lead markers. Clues to inappropriate pelvic positioning are loss of symmetry in the widths of the iliac alae, sizes of the obturator foramina, and positions of the "tear drop" figures.