A joint is a structure in the body, made up of two or more bones, that allows one bone to move against another. Movement through joints lets different parts of the body change positions. The hip is a ball and socket joint. Unlike a hinge joint, a ball and socket has multiple planes of movement. The socket is called the acetabulum. It is made up of portions of three bones—the ilium, the ischium, and the pubis. The femur is a single specific bone. At the hip joint, it is divided into several anatomic areas.
The round part, or the ball, is called the femoral head. The section below the ball is called the femoral neck. There are two bony prominences below the femoral neck. The outer prominence, the greater trochanter, is the large bony surface that you can feel on the outside of your hip. The abductor muscles, that pull your leg outward, attach to the greater trochanter. A smaller bump on the inside of the hip is called the lesser trochanter. This is where the main muscle that flexes the hip, the iliopsoas, attaches.
The region between the greater and lesser trochanters is called intertrochanteric. The part of the femur below the two trochanters is called subtrochanteric. The bone on the inner side of the femoral neck is called the calcar. The shaft of the femur is the long portion of the bone between the hip and the knee joints.
Several soft tissue structures are present around and within the hip joint. The lining of the hip joint is called the capsule. The back or posterior portion of the capsule supplies a large part of the blood supply to the head of the femur. The labrum is a ring of thick tissue called fibrocartilage around the edge of the socket. It adds depth to the socket and stability to the hip. The ligamentum teres is a thick ligament that extends from a portion of the acetabulum called acetabular notch to an area of the femur called the fovea. It carries a small portion of the blood supply to the femoral head.
Within the joint is a lining tissue called synovium. Synovial tissue is found in every large joint in the body. It secretes synovial fluid, which lubricates and nourishes the tissues inside the joint.
The surfaces of the joint are made up of smooth white tissue called articular cartilage. It is damage to the cartilage surfaces of the joint that usually creates the need for hip replacement surgery.Together all the parts of the joint combine to form a strong stable structure that allows for friction-free movement in many directions.