Osteoarthritis (OA) is the most common form of arthritis that affects joints. In a healthy joint, there is a cushion of articular cartilage and fluid between the two joint bones, allowing for the bones to move frictionlessly against each other. Degenerative wear and tear of joints causes this cartilage to wear away, leading to friction in the joint with movement. This friction causes inflammation, pain, and stiffness that worsens throughout the day. OA can occur in any joint, but it is most common in the knees.