Arthritis causes pain, stiffness and swelling from the inflammation of a joint or the area around joints.

The three basic types of arthritis that may cause hip and knee pain: osteoarthritis and inflammatory arthritis (most commonly rheumatoid arthritis), and traumatic arthritis.

Osteoarthritis  Joint disease that gets worse over time Characterized by the breakdown of the joint's cartilage Does not cause swelling in joints (not inflammatory) Cartilage that cushions the bones of the hip starts to erode, eventually allowing the bones to grind or rub together Causes pain and stiffness

Rheumatoid Arthritis Causes joint swelling (inflammatory condition) The immune system mistakenly attacks the tissue that lines and cushions the joints Cartilage wears away and the cushioning fluid in the joint (the synovium) becomes swollen Inflammation causes chemicals to be released that damage the cartilage and bone Causes pain and swelling

Traumatic Arthritis The culprit here is a serious hip injury or fracture that can lead to a condition called avascular necrosis where the blood supply to the ball portion (the femoral head) of the thighbone is cut off Lack of blood supply causes the femoral head of the thighbone to deteriorate, produce pain, and other symptoms