DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Normal and swollen (right) knees of a 14-year-old boy. The cause of the swelling is an effusion, an accumulation of fluid in a joint. This is usually due to injury, but in this case the cause is unknown. Treatment is by resting the joint.
Model release available. Property release not required.