Two parts comprise the hip joint: a ball on the upper end of the thigh bone (femur) called the femoral head, and a socket in the pelvis known as the acetabulum. In a normal hip, the head of the femur rotates freely within the smooth, concentric surface of the acetabulum. A smooth, low-friction coverage of “hyaline” cartilage lines the joint, and joint fluid lubricates the articulation to allow smooth, frictionless, smooth motion. The acetabulum is lined by the labrum, which is a highly innervated fibrocartilaginous structure. The labrum acts as a gasket seal between the femoral head and the acetabulum and adds to the joint stability by deepening the socket. The articulation is encapsulated by a joint capsule and ligamentous complex that further stabilizes the hip articulation. Injury and degeneration of any of these structures can cause hip pain sufficient for a patient to seek medical attention.