A hip dislocation is when the thighbone (femur) separates from the hip bone (pelvis). Specifically it is when the ball–shaped head of the femur (femoral head) separates from its cup–shaped socket in the hip bone, known as the acetabulum. The joint of the femur and pelvis (hip joint) is very stable, secured by both bony and soft-tissue constraints. With that, dislocation would require significant force which typically results from significant trauma such as from a motor vehicle collision or from a fall from elevation. Hip dislocations can also occur following a hip replacement or from a developmental abnormality known as hip dysplasia.

Hip dislocations are classified by fracture association and by the positioning of the dislocated femoral head. A posteriorly positioned head is the most common dislocation type. Hip dislocations are a medical emergency, requiring prompt placement of the femoral head back into the acetabulum (reduction). This reduction of the femoral head back into the hip socket is typically done under sedation and without surgery, through maneuvers including traction on the thighbone in line with the dislocation. If this is unsuccessful or if there is an associated fracture in need of repair, surgery is required. It often takes 2–3 months for a dislocated hip to fully heal, and it can take even longer depending on associated injuries such as fracture.

Typically, people with hip dislocations present with severe pain and an inability to move the affected leg. Diagnosis is made by physical exam and plain X-rays of the hips. A CT scan is recommended following reduction to rule out complications. Complications include osteonecrosis, femoral head fractures, and posttraumatic osteoarthritis.

Males are affected more often than females. Traumatic dislocations occurs most commonly in those 16 to 40 years old. Half of all hip dislocations are accompanied by a fracture. The condition was first described in the medical press in the early 1800s.