Articular cartilage is the smooth lining that covers the surfaces of the ball-and-socket joint of the hip. The cartilage gives the joint freedom of movement by decreasing friction. The layer of bone just below the articular cartilage is called subchondral bone . The main problem in OA is degeneration of the articular cartilage.
When the articular cartilage degenerates , or wears away, the subchondral bone is uncovered and rubs against bone. Small outgrowths called bone spurs or osteophytes may form in the joint.