What is Arthritis

The knee on the left is normal but on the right arthritis effects the medial compartment. The narrowing of the gap between the bones is an indicator of arthritis in this part of the knee.

Arthritis literally means “inflammation of a joint”. It is broadly divided into osteoarthritis and inflammatory (rheumatoid) arthritis. Gout is also a cause of arthritis when affecting the knee. This section deals with Osteoarthritis.

Osteoarthritis is a breakdown of the surface of the joint, the articular (hyaline) cartilage. Throughout life, the articular cartilage is subjected to the trauma of every day living and is a remarkably resilient tissue, which has a capacity to repair itself. It is therefore a balance between injury and repair and it appears that osteoarthritis presents a shifting of the balance as the repair process decompensates, results in incomplete healing and eventually breakdown of the joint surface. This is seen as fragmentation of the joint surface, producing debris which irritates the lining membrane of the knee, causing inflammation and excessive production of joint fluid (effusion). As the joint becomes painful, secondary changes take place, affecting the muscles and ligaments, which cause stiffening of the knee joint and weakness of the leg. In general, it becomes increasingly more difficult to walk.

An arthroscopic view of arthritis. The arrow points to bone which has appeared as the overlying articular cartilage has worn down.