Ball-and-socket joint between the head of the femur (thigh bone) and the pelvic girdle.
The hip joint resembles the shoulder joint, but is stronger and has less movement; the acetabulum (pelvic socket) is considerably deeper than the glenoid cavity of the shoulder joint. The capsule has three investing bands. The iliofemoral ligament connects the ilium to the femur, and in humans is mainly concerned in maintaining an erect posture. The other ligaments connect the femur with the pubis and the ischium (parts of the pelvis), respectively. The ligamentum teres, or round ligament, passes from a slight depression in the rounded head of the femur to the interior of the acetabulum. It is absent in some mammals. Gripping the head of the femur is a weak, flattened ligament which lies inside the capsule and deepens the margin of the socket; it is continued as the transverse ligament. The synovial (lubricated joint) cavity extends along the neck of the femur beyond the limits of the articular cartilages.
Diseases and injuries The hip joint is subject to the same diseases and injuries as other joints, including arthritis, dislocation, rheumatism, and tuberculosis. Congenital dislocation of one or both hips can occur. This is more common in girls than boys and is due to a structural failure in which the head of the femur is not contained within the pelvic socket, but lies above it. The leg on the affected side is shortened and there is a limitation of abduction (outward movement). Congenital dislocation may not be noticed until the child starts walking, when a characteristic rolling walk is observed.