Acetabular Fracture

Your hip is a deep ball-and-socket joint: the round head of your thigh bone (the femoral head) sits inside a cup-shaped socket built into the side of your pelvis. That socket is called the acetabulum, and it's not a single bone — it's where three pelvic bones meet, with cartilage lining the inside of the cup that the femoral head glides on. Anatomists describe the socket as having two main supporting struts, called the anterior column and posterior column, that meet at the top in the load-bearing roof of the cup (the dome).

An acetabular fracture means the cup itself has broken — almost always from high-energy trauma, when force is driven up the thigh bone and into the socket: a head-on car crash with a knee striking the dashboard, a fall from height, a major sports collision. The pattern of the break depends on exactly where your hip and knee were positioned at the moment of impact, which is why surgeons use a detailed system (the Letournel classification) that names roughly ten different fracture patterns based on which columns and walls broke.

Because the acetabulum is a weight-bearing joint surface, the goal of treatment is to restore the cup to its original shape as exactly as possible — within about two millimeters of where it started. Even a small step-off in the socket dramatically raises the long-term risk of post-traumatic arthritis, because the femoral head ends up grinding against an irregular surface every time you take a step. That's why these fractures, when they're displaced, are reconstructed in the operating room rather than rested into healing.

The mechanism is usually obvious — a major fall or crash followed by severe hip pain and an inability to put any weight through the leg. The exam looks for an associated hip dislocation (in many high-energy patterns the femoral head is driven straight out of the socket and has to be reduced back in immediately) and for any sign that the sciatic nerve, which runs right behind the back wall of the socket, has been stretched or pinched.

Imaging starts with three pelvic X-ray views: a straight-on (AP) view plus two angled views called Judet views that turn the socket so each column can be seen separately. A CT scan is then essential — it shows the exact fracture pattern in three dimensions, identifies any fragments of cartilage and bone that have broken loose into the joint, and is what surgical planning is built around.

Displaced fractures, fractures with the joint not sitting cleanly together (incongruity), unstable hips, and fractures with bone or cartilage fragments trapped inside the joint all need surgical reconstruction. The goal is to put the socket back together to within about two millimeters of its original anatomy — that's the threshold below which post-traumatic arthritis becomes much less likely. Acetabular reconstruction is highly specialized work and most often coordinated through a fellowship-trained pelvic trauma surgeon at a regional trauma center; OSI manages the long-arc recovery, follow-up imaging, and any later joint-replacement care if arthritis does eventually set in.

External patient-education references and related OSI pages for additional background:

• Britannica — Bone disease (fractures)
• Britannica — Hip (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language