Hip Overview
Summary
X-ray of a "Normal Hip"
"Hip" is the common name referring to the joint connecting the legs to the pelvis. This region includes the buttocks in the back (posterior), the trochanteric area on the sides (lateral), and the groin in the front (anterior). The hip joint has the important responsibility of bearing the entire weight of the upper body. Without healthy hips, stability, balance, and the ability to walk normally are compromised.
Arthritis of the hip, with the associated loss of healthy cartilage, is unfortunately common. There are many causes, including accidents (trauma), overuse (sports), diseases (rheumatoid arthritis, lupus, etc.), childhood conditions (slipped capital epiphysis, Perthes, etc.) and growth abnormalities (hip dysplasia, femoroacetabular impingement). Fortunately, the hip joint has been well studied. There are solutions that can treat many of these ailments and restore an individual to his or her previous quality of life.
Hip Anatomy
Anatomically, the hip is formed by two major parts, the pelvis, or acetabulum (i.e. hip socket), and the femur or femoral head (i.e. ball). The hip is commonly referred to as a 'ball-in-socket' joint. The acetabulum is formed by the contribution of three pelvic bones named the ilium, pubis, and ischium. Together these bones create a socket-like bowl that covers the femoral head. The upper part of the femur is a cartilage covered 'ball'. In a healthy patient, the spherical femoral head fits perfectly into the acetabulum with the help of the ring of cartilage (labrum) that surrounds the acetabulum. The labrum is analogous to the meniscus of the knee joint. In the hip, it serves as a gasket to maintain the synovial fluid lubrication of the hip joint.
While bones are the foundation for the hip, it is important to remember that muscles and ligaments, including the hip capsule, provide the support necessary for movement. The hip capsule has 3 major ligaments: the iliofemoral, ischiofemoral, and pubofemoral. Inside the joint, the ligamentum teres ligaments connect the femoral head to the acetabulum. As their names suggest, the first three ligaments listed are located on the outside of the acetabulum and attach to the corresponding pelvic bone its name suggests (i.e. iliofemoral attaches to the ilium, etc.). These ligaments help to control movement of the ball in the socket and to prevent dislocation of the ball from the socket.
Hip Movement
As any active individual knows, a healthy hip is necessary for most athletic activities. That being said, it is important to understand that there are 6 fundamental movements of the hip:
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Flexion: forward (anterior) movement of either leg
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Extension: backward (posterior) movement of the leg
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Abduction: movement of the leg away from the midline without rotation
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Adduction: movement of the leg toward (and past) the midline without rotation
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Internal Rotation: Rotating the left leg inwards
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External Rotation: Rotating the left leg outwards