Causes / typical injury mechanism: Acetabular fractures are intra-articular pelvis fractures that involve the socket of the hip joint, as opposed to pelvic ring fractures that do not involve the socket. The term "hip fracture" relates to the proximal femur that plugs into the socket and not the socket itself.

Classic history and presentation: Acetabular fractures have a bimodal age and sex distribution. A motor vehicle crash or fall from a height can cause an acetabular fracture in any age group. Most acetabular fractures after falling from a standing height occur in older adult women with underlying osteoporosis.

Prevalence: Acetabular fractures are about 3% of all skeletal injuries.

• Age – Bimodal distribution; seen in younger, active adults and individuals older than 65 years.
• Sex / gender – Osteoporotic fractures are more common in women.

Risk factors:

• Low bone mass or osteoporosis
• Smoking
• Low-estrogen states in women, such as from a prior hysterectomy or postmenopause
• Older age
• Northern European ethnicity
• Tobacco use
• Conditions that increase the risk of falling, such as alcohol use, prior fracture / fall history, and the use of fall-increasing drugs (eg, sedatives, opioids, dopaminergic agents, and anxiolytics / antidepressants)

Pathophysiology: The acetabulum is formed by the junction of the ilium, ischium, and pubis that creates an "inverted Y" made from the anterior and posterior columns, anterior and posterior walls, and the roof of the hip socket. It is lined with articular cartilage and matches the spherical shape of the femoral head.

Acetabular fractures occur when the femoral head is forcefully driven into the socket, exceeding the strength of the bone. The force's direction and magnitude determine the fracture pattern and could dislocate the hip joint. If the posterior wall is fractured, the hip joint could dislocate posteriorly and injure the sciatic nerve.

Grade / classification system: Most classifications, such as the Letournel classification system, rely on the anatomy and fracture pattern without referring to other factors that affect treatment decisions and outcomes, such as the degree of comminution and bone quality.

Letournel classification to determine the fracture pattern:

• What columns are involved (ie, anterior, posterior, or both)?
• Any separate wall involvement (ie, anterior, posterior, or both)?
• Is there any articular cartilage in continuity to the axial skeleton? (If yes, this is automatically considered a both column injury.)