Hip dislocation

The hip joint consists of the ball-shaped femoral head sitting in a concave socket in the pelvis (the acetabulum). The ball can rotate in almost every direction within the socket, allowing you to walk, sit, and run. At the same time, it sits deep in the socket and is firmly held in place by a thick joint capsule, strong ligaments, and a ring of cartilage around the socket's rim (the acetabular labrum), so it does not come out easily.

A hip dislocation is a complete displacement of this ball-and-socket relationship. When the joint shifts but its surfaces remain partially in contact, this is called a subluxation and is considered separately.

Traumatic dislocations in adults occur when a large external force is applied, such as in a car collision, a fall from a height, or a forceful impact during sports. Dislocations in people with an artificial joint or a joint shape that has differed since birth are discussed in a separate context, so this article focuses on traumatic dislocations of the natural hip joint.

Dislocations are classified according to the direction in which the ball moves relative to the socket.

A typical example of how a posterior dislocation occurs is when, during a car collision, the hip is bent and the knee strikes the seat in front, transmitting force backward.

A dislocation causes immediate, severe pain, and moving the leg or bearing weight becomes almost impossible. In a posterior dislocation, the injured leg is typically described as appearing shorter, with the knee and toes turned inward. In an anterior dislocation, the leg may appear spread outward.

The direction is not determined from the leg's appearance alone; it is assessed using imaging such as X-rays and CT scans together with a physical examination. Do not try to put the joint back in place yourself. It is safer to remain still and be transported by calling South Korea's 119 emergency ambulance service.

A dislocation is an emergency, so the hospital performs a procedure called 'reduction' to return the ball to the socket as soon as possible. Because pain and muscle tension are severe, medical staff usually carefully move the leg back into place under anesthesia or sedation. Imaging is then used to check that the ball is properly positioned and that no bone fragments are trapped in the joint. Surgery is performed to address these issues if necessary.

After reduction, recovery involves limiting weight-bearing and the angle to which the joint is bent for a period of time. The duration and approach depend on the extent of the injury, so follow the treating medical team's guidance. Rehabilitation exercises follow to restore strength and range of motion.

Because the hip is a highly stable joint, a complete dislocation often affects the surrounding structures as well. The following are therefore also checked after reduction.

• Whether there are fractures of the socket (acetabulum), ball (femoral head), or neck of the thighbone
• The condition of the sciatic nerve, which passes behind the hip (whether the ankle and toes move well and whether sensation is present)
• Blood flow to the ball. Problems with blood flow can lead to osteonecrosis over time, so follow-up monitoring is carried out after a dislocation.

Not every dislocation leads to osteonecrosis. Rather, because blood supply is directly linked to the survival of bone tissue, reduction is performed promptly and recovery is monitored afterward.

Hip pain, noises, and stiffness describe a much broader range of symptoms, whereas a dislocation refers to a structural state in which the ball and socket are completely displaced. Clicking sounds or sharp, tingling sensations while walking are usually unrelated to dislocation. Femoroacetabular impingement and developmental dysplasia of the hip are also distinct structural conditions of the hip.

Severe hip pain immediately after an accident or forceful impact, together with an unusual leg position or a complete inability to bear weight, requires immediate emergency care. Even after a dislocation has been reduced, seek reassessment if you have numbness or tingling and weakness in the foot or toes, or persistent groin pain and limping.