Osteoarthritis: Causes and diagnosis
If you are in your 60s as you read this, it's a good bet that you have osteoarthritis (OA). If you are in your 80s, it's a sure thing. But that doesn't mean your joints are bound to become stiff, swollen, or painful, since about two-thirds of the people who have x-ray evidence of OA don't have any symptoms. On the other hand, many people who blame their aches and pains on arthritis are actually suffering from something else. Despite its very high prevalence in older people, arthritis is often misunderstood — and mistreated.
The normal joint
From an engineer's point of view, every joint is a compromise. Joints have to perform two contradictory functions: They have to be flexible, to allow smooth movement, but they also have to be stable, to support weight and absorb tremendous force without wavering. Different joints meet these challenges in different ways, but they all have some common features.
Joints are found at the junction of two (or more) bones. Muscles attach to the bones through their strong fibrous tendons. To move a joint, some of the muscles contract, pulling on the tendons and bones. For smooth, painless motion, though, the muscles on the opposite side of the joint must relax. For example, when you bend your elbow, your biceps contract but your triceps relax.