Being double jointed means that you can bend your joints more than the average person. There are many misunderstandings when it comes to the meaning of being double jointed. In one case, the term itself implies that double jointed people have twice the number of joints than normal human beings. Some even assume that double joints allow for twice the usual amount of motion. However, these meanings are myths. All human beings have the same number of bones and joints, all of which have similar capacities for movement.
If you are double jointed, it means that your joints and their surrounding structures, known as ligaments and tendons, are unusually flexible, enabling you to bend or rotate them in ways that some people find impossible and painful. Furthermore, you are able to stretch your joints, ligaments and tendons to a greater extent than commonly experienced by people with average flexibility. For instance, there are circus performers who can bend their bodies to the back from the waist, locking their heads in between their legs. Other double jointed people can bend their thumbs the wrong way until the tips touch their hands.
From a medical viewpoint, being double jointed is also known as having hypermobility. Double jointed people are not overextending their joints, but are rather allowing them to function to their fullest capability. It just so happens that this capability is beyond the typical person's ability for movement.
How does it happen?
Joints are the hinges that connect two or more bones together, allowing motion and movement to occur naturally in a particular direction. Ball-and-socket joints, however, are joints in which the rounded end of a bone fits into the hollow of another, allowing rotary movement in every direction. The opening or hollow in which the bones sit is called a socket. The depth of a socket determines the flexibility of that joint. Cartilage, a firm fibrous tissue made up of a protein called collagen, cushions bones at joints and is another factor that affects joint pliancy.
Extreme flexibility in double jointed people can be caused by a combination of several factors. Double jointed people can have a very shallow socket, enabling more movement in both directions. Where ball-and-socket joints are concerned, some people with double joints can intentionally and painlessly dislocate the bone completely from its socket and then move it back into position again. Shallow sockets, combined with bone ends that are smoother than normal, also help joints slip and move easily in any direction. Ligaments and cartilage that stretch beyond the usual extent impact joint flexibility in the same way. For some people, being double jointed can be very painful and impose moderate to severe limitations in daily life.
We have all been double jointed at some point in our lives. A good example can be taken from our childhood, when we could bend from the waist and touch the tips of our fingers to the floor while keeping our legs straight. Typically as we age, our ligaments, cartilage and bones harden, losing their suppleness. There are syndromes associated with hypermobility that can cause pain and impact health and well-being.