Occult central fractures of the acetabulum.

Four cases of occult central acetabular fractures are presented. The oblique plane of the fracture line and the lack of displacement of the fracture fragments made the fractures difficult of impossible to visualize in the anteroposterior projection. The posterior oblique projection placed the fracture line perpendicular to the x-ray beam and, therefore, evident on the resultant roentgenogram. In the 3 cases in which this view was obtained, the fracture was disclosed. In the fourth case the fracture was demonstrated by tomography. In order to improve the roentgenographic assessment of pelvic trauma, consideration should be given to obtaining posterior oblique views of the pelvis as a matter of routine.