Articular cartilage covers the moving surfaces inside the knee. Articular cartilage is very smooth and has very low friction. Articular cartilage is the "tread" inside your knee. Articular cartilage is living tissue, but it has limited potential for growth and repair. As with all tissue, the potential for growth and repair of articular cartilage decreases with age. If the loads on the joint, or on a portion of the joint, are too high, either because of improper alignment, incongruency, excessive weight, extreme activities, or a combination of these factors, articular cartilage will degenerate and be worn away. The process of articular cartilage degeneration is a source of inflammation. This can result in pain, swelling and progressive loss of motion. In advanced arthritis, the articular cartilage has been completely worn away and the bone of the femur and tibia, and the femur and patella, come into direct contact. This is generally accompanied by significant pain, a decrease in motion (stiffness), muscle weakness, and difficulty walking. The main reason to have a total knee replacement is because of severe pain that is due to extensive loss of articular cartilage.

Wear of articular cartilage can be seen on x-rays as a decrease in the space between the bones. In general, extensive loss of articular cartilage is accompanied by extensive loss of meniscal cartilage. When the cartilage is completely worn away, the x-rays show that the bones are now in direct contact. Loss of articular cartilage increases the amount of stress on the ends of the bones resulting in the growth of bone spurs, or osteophytes, at the margins of the joint. Front and side x-ray views of an arthritic knee are shown in Figures 2A and 2B respectively. On the front view (Figure 2A), note the absence of space between the bones as indicated by the arrows. This loss of joint space occurs because the articular cartilage has worn away. The bone reacts to the loss of cartilage by making bone spurs (osteophytes). These bone spurs can be seen on the side view (Figure 2B) as indicated by the arrows.

 

2A	2B