The hip is a classic ball-and-socket joint. The ball is the femoral head, which is the upper end of the femur (thighbone). The socket is formed by the acetabulum, which is part of the large pelvis bone. Articular cartilage is a slick, slippery tissue which covers the surface of all diarthrodial joints, in this case, the ball and the socket. It creates a smooth, nearly frictionless surface that helps the bones glide easily across each other.
The acetabulum is ringed by strong fibrocartilage called the labrum. This tissue is nearly identical to the labrum in our shoulder or meniscus in our knee. The labrum forms a gasket-like seal around the socket. The joint is surrounded by the capsule which is dense, sleeve of highly organized collagen-fibers which connects the acetabulum to the femoral neck.
There are areas of more condensed, specialized bands of tissue called ligaments. The inner surface of the capsule is lined by a thin layer of cells called the synovium. It produces synovial fluid that lubricates the hip joint. In a healthy hip, the femoral head fits perfectly into the acetabulum.