The hip joint is considered a ball-and-socket joint in which the ball of the femoral head articulates with the socket (also called acetabulum) which is a hemispherical cavity in the pelvic bone. The hip joint is very stable because of this configuration and because of the strong muscles and ligaments surrounding it.
However, severe trauma (e.g. motor car accidents and fall from heights) may cause dislocation of the hip, damaging the ligaments, muscles, and other soft tissues holding the bones in place. Adjacent nerves may also be injured. In about 90% of cases the femoral head is dislocated in a posterior (backward) direction and rarely does it dislocate anteriorly. The patient suffers severe pain and is unable to move his leg which become fixed in an abnormal position.
This injury is considered a medical emergency and the treating doctor will examine the patient to and ask for X-rays and CT scan to confirm the diagnosis and to detect any associated injuries. If there is no associated injury the patient is given an anesthetic and the doctor will reduce the hip to its normal position. After reduction, new x-rays and CT scan are usually required to confirm that the joint is in its normal position and there are no loose bony fragments inside the joint. If loose fragments are found in the joint, surgery may be required to remove it to prevent it from causing damage to the joint cartilage.
- Nerve injuries: when the femoral head dislocates posteriorly, it may injure the sciatic nerve which is a major nerve supplying the leg. The nerve usually recovers gradually by time.
- Avascular necrosis: the dislocation may damage the blood supply to the femoral head leading to a condition called avascular necrosis.
- Osteoarthritis: the massive trauma required to dislocate the hip joint usually leads to a variable extent of cartilage damage. By time, this may cause osteoarthritis of the hip joint.