Osteoarthritis

Osteoarthritis is a very common condition that essentially results from degeneration of articular cartilage through wear and tear, although there are also genetic factors involved in its development. Eventually, the cartilage is worn away completely. The process is accelerated if there is previous joint damage or deformity of any type.

In the initial stages, the articular hyaline cartilage becomes soft and weak owing to an increased amount of water, decreased concentration of proteoglycans and weakening of collagen in the matrix. Chondrocytes adjacent to the bone proliferate and produce new matrix in an attempt to replace the abnormal cartilage, but eventually this process fails and the degenerative changes supervene.

Figure 3.60.1 shows some of the morphological changes in osteoarthritis. In the early stages, the surface of the hyaline cartilage becomes ragged and split, an appearance known as fibrillation. The subchondral bone becomes sclerotic through thickening of the bony trabeculae. Later, proliferation of bone at the edge of the joint produces irregular nodules called osteophytes. There is a chronic inflammatory infiltrate of the synovium and surrounding tissues, but it is not as marked as in rheumatoid arthritis. If the cartilage wears away completely, the underlying bone becomes polished smooth and comes to resemble ivory, a process known as eburnation. Cyst-like spaces form in the bone underlying the joint as synovial fluid is forced into it through microfractures.

Fig. 3.60.1 Part of a typical synovial joint surface to show changes in osteoarthritis.

Clinically, osteoarthritis typically affects the hips and knees, cervical vertebrae, hands and wrists. However, any joint can be affected, especially if it has been previously injured. Symptoms include pain, stiffness and swelling of the joint.