Hip Anatomy

The hip joint is the most flexible free-moving joint in the body, as well as one of its largest weight-bearing joints. Essentially a ball-and-socket joint formed where the rounded "ball" of the femur (your upper leg bone) joins the cup-shaped socket (the acetabulum) of your pelvic bone, the hip can move backwards and forwards, from side-to-side, and perform twisting motions.

A normal, healthy hip allows you to walk, turn, and squat without pain. Full function of the hip joint depends on the successful coordination of many interrelated parts, including bones, muscles, tendons, ligaments, and nerves. Like other free-moving synovial (movable) joints, the hip contains a small amount of clear, oil-like fluid that lubricates the joint whenever you move it.

Smooth soft tissue called cartilage helps prevent the joint from dislocating and assists both the muscles that power hip leg movement and the tendons that attach those muscles to the bones.

Age, injury and disease can cause the hip's cartilage to wear down. Without sufficient cartilage to serve as a cushion, the bones begin to rub together, gradually becoming rough and irregular. As a result, the ball eventually grinds in the hip socket when you move your leg, causing pain and stiffness.

Normal Hip	Osteoarthritic Hip	Rheumatoid Hip	Fractured Hip

Osteoarthritic Hip
In osteoarthritis, the cartilage cushioning the bone surfaces wears away, causing the bones to painfully rub against each other.

Traumatic arthritis results when the joint (or the ligaments surrounding it) is damaged by fracture, dislocation or accident-related injury. The resulting arthritic condition may cause stiffness, swelling and loss of motion. As the joint becomes increasingly tender and swollen, it may become increasingly difficult to put pressure on the hip. Over time, arthritis of the hip and the resulting arthritis hip pain can significantly affect your ability to walk.

Rheumatoid Hip
Another form of arthritis, known as rheumatoid arthritis, occurs when the body's own immune system attacks the synovial lining of the joints, just as it would a foreign bacteria. As the lining becomes increasingly inflamed, the joint's cartilage is damaged, and the hip becomes stiff and sore.

Fractured Hip
A fracture, or break, in one of the hip's components can impede movement, create irregularities and cause pain. Fracture sites may also later become osteoarthritic.

Compare the following images of a biological hip and a hip prosthesis.