Did you know that there are six distinct types of synovial joints that all work together to provide the human body with its impressive range of motion? While some of these joints—like the gliding joint in the knee—are quite complex, the joints that grant us the greatest freedom of movement appear remarkably simple. In fact, these specialized joints are so flexible and useful that they’re often mimicked in the designs of industrial engineers. You can even find an approximation of this joint in the steering mechanism of your car.
I’m talking, of course, about the humble ball-and-socket joint.
Also known as a spheroidal joint, the ball-and-socket joint is classified as a multiaxial joint because it allows bones to move freely along several different axes. In the human body, these joints can be found in the hips and shoulders, giving our limbs the freedom of motion they need to do things like run, jump and even hurl projectiles hundreds of meters through the air.
As you can see in this illustration, however, a ball-and-socket joint consists of more than just one rounded bone fitted into the concave depression of another.
Because these joints offer such a wide range of motion, they require a great deal of support from connecting ligaments and muscles. The hip joints, in particular, need plenty of support and stability from the surrounding musculature, which is why they are not quite as flexible as the ball-and-socket joints in our shoulders. The interior surfaces of these joints are also protected by a special layer of cartilage that allows them to move smoothly against one another.
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