Cartilage normally protects the joint, allowing for smooth movement. Cartilage also absorbs shock when pressure is placed on the joint, like when walking. Arthritis involves the breakdown of cartilage. Without the usual amount of cartilage, the bones of the joint rub together, causing pain, swelling and stiffness.
Update Date 1/22/2014
Updated by: Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.