Changes In Joint Cartilage
Symptoms of osteoarthritis result from changes in hyaline cartilage. Hyaline cartilage normally separates and cushions the bones within a joint, protecting them from impact while allowing smooth joint motion. This type of cartilage undergoes biochemical changes that lead to abnormalities in both the cartilage itself and the bony surfaces that face one another within a joint.
The cartilage surface, which is normally very slick and smooth, becomes irregular and then begins to thin out in some areas. This thinning eventually can lead to large areas of complete cartilage loss. Joint pain and the loss of joint motion associated with osteoarthritis result from bones rubbing against one another within the joint, as well as from increased stress on nearby tendons, muscles and ligaments.
Bone spurs (that is, extra bone), called osteophytes, may form as a reaction to the abnormal stresses placed on the joint. These spurs may cause the joint to enlarge and press on other nearby structures such as nerves or tendons. This can lead to significant pain, further limitations in joint motion, tendonitis and other problems. Cartilage heals poorly, if at all, so the damage in osteoarthritis tends to accumulate over time and rarely improves on its own.
Some joints seem to be more prone to osteoarthritis than others are, probably because of their anatomy and the way they are used. For example, a lifetime of weight-bearing activities seems to make the hips and knees more vulnerable to osteoarthritis than are other joints that don't bear weight, such as the elbows. It remains unknown, however, why the ankles are frequently spared, even though they are also weight bearing, or why the hands are commonly affected, even though they are not weight bearing.