Hip Dislocation

A hip dislocation is when the ball at the top of your thigh bone gets forced out of the socket in your pelvis. Most of the time (about 90% of cases) the ball pops out the back — usually after a high-energy impact like a car accident, a sports collision, or a fall from height. The classic mechanism is a knee striking a dashboard and driving the hip backward. The opposite direction (out the front) is less common and happens when the leg is forced wide and rotated outward.

Hip dislocation is a true emergency. The arteries that supply blood to the ball of the hip run alongside the back of the joint capsule — and the longer the hip stays dislocated, the higher the risk those vessels are stretched or torn. After about 6 hours, the chance of the ball losing its blood supply (avascular necrosis) rises sharply. Up to half of dislocations come with associated fractures of the ball, the socket rim, or the neck of the thigh bone.

After a posterior dislocation — the most common type — your leg looks obviously abnormal: shortened, rotated inward, and drawn toward the midline. The pain is immediate and severe, and you cannot move the hip at all. These injuries nearly always follow a major impact such as a car crash or a high-speed sports collision.

Numbness or tingling running down the back of the thigh and leg can signal that the sciatic nerve — which passes directly behind the hip joint — has been stretched or compressed by the dislocated ball. About 10–15% of posterior hip dislocations involve a sciatic nerve injury. Any associated fracture of the socket rim (acetabular fracture) or femoral head adds to the swelling and may trap bone fragments inside the joint.

A posterior hip dislocation is unmistakable: severe pain, the affected leg looks shorter than the other, rotated inward, and pulled toward the midline. A standard pelvis X-ray confirms the diagnosis. After the hip is put back into place, a CT scan is essential — it picks up associated fractures and any loose pieces of cartilage or bone trapped inside the joint. Your surgeon will also carefully check the function of the sciatic nerve, which runs right behind the joint and can be stretched or pinched in a posterior dislocation.

Surgery is needed when the hip can't be put back into place by manipulation alone, when associated fractures need to be fixed, or when loose pieces of bone or cartilage in the joint need to be removed.

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

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