Fatigue fracture of the sacral bone associated with septic arthritis of the symphysis pubis.

Fractures of the pubic rami are almost invariably associated with fractures of the posterior arch of the pelvic ring. Two women, aged 50 and 67 years, with septic arthritis of the symphysis pubis attended by severe low back pain, were followed with CT and MR imaging of the pelvis, as well as bond scintigraphy in one patient. In the first patient sacral fractures with severe displacement were revealed, prompting stabilizing symphysiodesis. In the second patient an undisplaced fatigue fracture was confirmed in the right half of the sacrum. In patients with pelvic laxity following arthritis of the symphysis and post-traumatic osteolysis associated with low back pain, displaced or occult fractures of the bones adjacent to the sacroiliac joints should be considered.