The most common form of arthritis, osteoarthritis is because of the progressive wearing down of cartilage over time. This restrictions the array of motion and triggers pain, stiffness, weak spot and swelling on the knee. Pseudogout is usually mistaken for gout but it's a result of calcium-made up of crystals https://www.theorthopaedicandpainpractice.com/knee-pain-in-older-patients-ages-55/