The hip is a ball-and-socket joint that allows the leg to move in a variety of positions. The femoral head (ball) rides in the acetabulum (socket). The joint is lined with a lubricating tissue called cartilage, which cushions the joint as it moves and bears weight.
Osteoarthritis, the most common form of arthritis, is a wear and tear condition that destroys joint cartilage, and it typically develops after years of constant motion and pressure in the joints. As the cartilage continues to wear away, bone begins to rub against bone, causing the irritation, swelling, stiffness, and discomfort commonly associated with arthritis.