OA, the most common form of arthritis, occurs in about 21 million Americans. Of all the weight-bearing joints, the knee is most commonly affected by OA. Knee OA leads to physical changes to the entire joint structure, including cartilage, neighboring bone, and ligaments. Such structural changes to the knee alter joint function during movement, resulting in pain. The pain typically leads to less physical activity, leading to weight gain, followed by impaired physical function and disability.