Acetabulum · What Is It, Function, Fractures, and More

The acetabulum is a large socket on the lateral face of the hip bone that articulates with the head of the femur to form the hip joint.  

Anatomically, the acetabulum is formed by the fusion of the three pelvic bones: the ilium, ischium, and pubis. The ilium forms the upper boundary of the acetabulum, the ischium contributes to the posterior wall, and the pubis forms the anterior wall. In addition, the acetabulum is divided into an anterior and posterior column. The anterior column includes the anterior half of the iliac wing and the anterior half of the acetabular surface, whereas the posterior column begins at the greater sciatic notch and includes the posterior half of the acetabulum and ischial tuberosity. This distinction between acetabular walls and columns facilitates the classification of acetabular fractures.  

Acetabular fractures are pelvic fractures that involve the articular surface of the hip joint. These fractures occur primarily in young individuals who are involved in high-energy trauma such as motor vehicle crashes, falls from height, and sporting accidents. Less frequently, they may also occur in elderly individuals with poor bone density after a fall from standing height. Because acetabular fractures are usually caused by high-energy trauma, they’re often associated with other life-threatening injuries, including pelvic ring and lower extremity fractures; nervous and vascular injuries; and head, chest, or abdominal trauma. 

Diagnosis of acetabular fractures can be made with plain X-ray imaging, although a CT scan is commonly conducted to investigate other potential injuries and for surgical planning. Usually, a series of radiographs is obtained, including an anteroposterior view (AP) of the pelvis and Judet views. The Judet views are obtained to assess the integrity of the acetabular columns, and they consist of an obturator oblique and an iliac oblique view. The obturator oblique view is conducted to assess the anterior column and posterior wall of the acetabulum, whereas the iliac oblique view allows for assessment of the posterior column and anterior wall.  

There are several acetabular fracture classification systems with the most commonly used being the Letournel and Judet classification. This system classifies fractures of the acetabulum into five elementary types and five associated, or combined, types. By far, the most common type of fracture is a posterior wall fracture, which typically occurs when an individual is in a seated position and the knee hits the dashboard during a car crash. This pushes the femur against the posterior wall of the acetabulum, causing an impaction of the femoral head on the posterior acetabular rim. Posterior wall fractures may be accompanied by a posterior hip dislocation and injury to the sciatic nerve, which runs just posterior to the acetabulum.