This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The flaring wings or alae of the ilium are not infrequently fractured by direct violence. The line of fracture is usually transverse (Fig. 493). The displacement is slight on account of the muscular attachments of the iliacus muscle inside and the glutei muscles outside. The anterior third of the crest of the ilium is subcutaneous and prominent, hence by manipulating it crepitus can usually be elicited and the diagnosis made. Recumbency and the support afforded by adhesive plaster is all the treatment necessary.
The more serious fractures, however, are those of the true pelvis. The pelvic cavity is somewhat heart-shaped; the sacrum projects anteriorly and is so strong that it is rarely fractured. At or just outside of the sacro-iliac joints is, however, one weak point; between the acetabulum and the pubes, through the rami of the pubes and ischium and thyroid foramen, is another; and at the symphysis is a third.
The most frequent fracture passes through the pelvic ring twice, anteriorly through the rami of the pubis and ischium and thyroid foramen and posteriorly through or just external to the sacro-iliac joint. Whenever a fracture of the pelvis is suspected, search for this fracture. Examine the rami of the pubes. Pressure made along Poupart's ligament just external to the spine of the pubes will usually reveal a tender spot and may elicit crepitus. A digital examination through the rectum or vagina may likewise indicate the site of the fracture. The bladder is frequently wounded, the rectum almost never and the urethra rarely.
The symphysis, while comparatively a weak part is rarely the site of injury. In childbirth the attachment of the pubes to each other becomes relaxed and a slight physiological separation occurs.
Fig. 493. - Diagram illustrating fracture of the pelvis; one fracture is seen passing through the ilium; the other passes through the sacro-iliac articulation posteriorly and the thyroid foramen anteriorly.