What is Double-Jointed?

By April Cashin-Garbutt, BA Hons (Cantab)

Is there really such a thing as being double-jointed?

With the increasing rise of reality TV talent shows, most of us have seen amazing contortionists perform. But have you ever wondered how do they do it? And is there really such a thing as being double-jointed?

Can people really be double jointed?

In short: yes they can. Double-jointedness, or joint hyperlaxity/hypermobility as it is correctly called, is in fact a medical condition that is thought to affect around 3% of the population.

Like most things in life, however, nature is only part of the story: nurture, of course, plays its role too. Essentially, the extreme body movements that contortionists make are both a result of their own genetic make-up, and many hours of training.

In fact, doctors still don’t fully understand how contortionists can accomplish some of their moves. When speaking to the BBC about a study on the spine of a contortionist, Dr Wiseman said, “We still don’t fully understand what’s happening”.

What causes double-jointedness?

There are many potential causes of double jointedness. In fact, according to the Hypermobility Syndrome Association (HMSA) it is probably more appropriate to refer to hypermobility as a family of related conditions rather than a single one.

One cause of double jointedness can simply be the shape of the bones themselves. For example, a shallower joint socket will permit more movement of the limb than a deeper one.

Collagen constitution

Another contributing factor to joint hypermobility is a person’s genetic instructions for making the protein collagen. Collagen is found in ligaments, which are what connect bones together at a joint.

If the genetic instructions are so that the collagen is relatively weak, then this will mean that ligaments are more easily stretched, and thus the joints are more flexible.

Specifically, researchers at the University of Washington have found that people with certain deletions in the 1q21.1 chromosome exhibit joint hypermobility.

Hormones are also thought to influence flexibility by affecting collagen. In particular, the hormone oestrogen is thought to be linked to flexibility. This is because women tend to be more flexible than men, and also women tend to be less supple once they’ve have been through the menopause.

Hypotonia

Hypotonia is where a person has decreased muscle tone. This occurs when the brain does not send the usual signals to the muscles to tell them to contract. Consequently, the small amount of contraction, that is normally present in muscles all the time, does not occur and thus the body may possess a floppy characteristic. For example, the arms and legs may hang by the sides.

This floppy quality means that the body is more flexible, for there is less muscular resistance to unusual movements.

Hypotonia is caused by damage to the brain, nerves or muscles. Such damage can be caused in a number of ways including both genetic and environmental methods. Some genetic causes are: Down’s syndrome, muscular dystrophy, Prader-Willi syndrome, myotonic dystrophy and Tay-Sachs disease.

Problems with proprioception

Proprioception literally means “one’s own”. It refers to our ability to constantly sense the position of our body and its parts. For example, even when your eyes are closed you should still be able to sense what position your legs and arms are in.

People who have problems with proprioception are able to move their limbs in more unusual ways. This is because they are not conscious that their joints are overstretched.

More serious causes

Joint hypermobility can also be caused by more serious conditions such as Marfan Syndrome, Ehlers-Danlos Syndrome Vascular Type (EDS IV) and Osteogenesis imperfecta. These have potentially serious complications.

Advantages of double-jointedness

In addition to being an advantage if you’re trying to win a talent competition, double-jointedness also has many other advantages.

Hypermobility can be very useful in some sports. For example in cricket: bowlers with long, thin, flexible fingers are likely to be able to produce better spin on the ball when they bowl.

Music is another obvious example in which hypermobility may come in very useful. For example, playing the piano or guitar would be much easier if you were to have hypermobile fingers.

The downsides of double-jointedness

Although double-jointedness may have its advantages, it does, of course, have many downsides.

In fact, the very point that many people, including some doctors, view double-jointedness as so advantageous can be problematic in itself.

For example, Jay Kitson-Jones from HMSA told the BBC that people do not take the condition seriously. Such lack of understanding of the condition can itself have an emotional influence on those with it. Many suffer from frustration, anger and even depression.

In addition to these mental symptoms, there are many physical problems. The main problem is joint pain. This occurs particularly during growth spurts in females.

Another downside is that people with hypermobility syndrome tend to be more likely to endure painful injuries such as dislocation, fractures, disc prolapse, ligament sprains, muscle strains, pulled tendons and so forth.

Sources:

http://news.bbc.co.uk/1/hi/health/7523248.stm

http://news.bbc.co.uk/1/hi/uk/3271309.stm

http://www.hypermobility.org/whatishms.php

http://www.nhs.uk/Conditions/Joint-hypermobility/Pages/Causes.aspx

http://www.nejm.org/doi/pdf/10.1056/NEJMoa0805384

http://www.ninds.nih.gov/disorders/hypotonia/hypotonia.htm

http://www.iadms.org/associations/2991/files/info/proprioception.pdf

http://www.hypermobility.org/painandhms.php

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