The knee is a type of hinge joint formed by the tibia (shinbone), femur (thighbone), and patella (kneecap). The ends of the bones in the knee joint are covered with cartilage, a tough, lubricating tissue that helps provide smooth, pain-free motion to the joint.

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.