Osteoarthritis of the knee before and after replacement

Panel A shows an X-ray of a knee affected by arthritis. Panel B shows the same knee after surgery to replace the knee. In panel A, the arrow shows that the space between the thighbone (called the femur) and the shinbone (called the tibia) has narrowed. This has caused the bones to grind against each other and form spurs. In panel B, the femur and tibia each have new metal end-pieces. The arrow shows that the space between the two bones has been widened with a plastic spacer.