Читать книгу Arthritis For Dummies - Barry Fox - Страница 13

Before you can understand what’s wrong with your joints, you need to understand what a joint is and how it works. Any place in the body where two bones meet is called a joint such as the ball and socket hip joint, or the hinge joint at the elbow or knee. Sometimes the bones actually fuse together; your skull is an example of an area with fused bones. But in the joints that can develop arthritis, the bones don’t actually touch. As you can see in Figure 1-1, a small amount of space exists between the two bone ends. The space between the ends of the bones keeps them from grinding against each other and wearing each other down.

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FIGURE 1-1: Anatomy of a healthy synovial joint.

Bones are living tissue — hard, porous structures with a blood supply and nerves — that constantly rebuild themselves. Bones protect our vital organs and provide the supporting framework for the body. Without bones, we would be nothing more than blobs of tissue — like tents without supporting poles!

But bones are more than broomsticks that prop us up; fortunately, they don’t leave us rigid and awkward. The 200-plus bones that reside in our bodies are connected together in some 150 joints, giving us remarkable flexibility and range of motion. If you don’t believe it, just watch a gymnast, ballet dancer, or figure skater execute a handspring, arabesque, or triple axel. But you don’t have to be an athlete or contortionist to enjoy the benefits of joint flexibility. Just think about some of the things you do regularly — such as bending a knee or an elbow. Now imagine how limiting it would be if you had fewer joints, or if they didn’t move the way they do! (For a few fascinating facts about your joints, see the sidebar “Strange-but-true joint points” on the next page.)

Other structures surrounding the joint, such as the muscles, tendons, and bursae — small sacs of fluid that cushion the tendons like pillows — support the joint and provide the power that makes the bones move. The joint capsule wraps itself around the joint, and its special lining, the synovial membrane or synovium, makes a slick, slippery liquid called the synovial fluid. You can think of the joint capsule as a sealed bag full of WD-40 encasing the joint and filling the little space between the bone ends. Finally, the bone ends are capped by cartilage — a slick, tough, rubbery material that is eight times more slippery than ice and a better shock absorber than the tires and springs on your car! Together, these parts make up the joint, one of the most fascinating bits of machinery found in the body.