Growing up we all knew that one kid who just happened to be so flexible they could twist their shoulder (or leg or hand) in a weird way and freak everyone out a bit in the process. That kid isn't alone: In fact, it's estimated that around 20% of adults show some form of double-jointedness (so maybe you were that kid). But unfortunately, the term is pretty misleading — and, for some, the condition can come with painful side effects.
If you're double-jointed, I'm sorry to say you don't literally have an extra joint. But you do have an innate and impressive flexibility in that particular spot, sometimes referred to as "hypermobility." So how is this possible if you're stuck with the normal amount of joints?
For most of us, these bits of tissue are somewhat stretchy, but have their limits. However, some people are able to stretch their tendons and ligaments far beyond what the rest of us are capable of, without special training or much discomfort. This is how some people are able to pull their thumb back to meet their wrist, for instance. We don't know too much about why only some people are able to do this, but research suggests that individual differences in the way certain bones are shaped may contribute — and that there's a genetic basis for the ability.
For the most part, being double-jointed isn't a harmful thing. However, it's not all party tricks: According to Edward R. Laskowski, MD, at the Mayo Clinic, hypermobility can also cause chronic pain and frequent injuries and dislocations for some. In those cases, doctors often recommend physical therapy to strengthen and stabilize the loose joints.
In rare instances, though, extreme flexibility can be a sign of a more serious condition, such as Marfan syndrome. However, double-jointedness wont be your only symptom in those cases —Marfan syndrome often comes with severe vision and heart problems.
Still, if you're concerned about being double-jointed or you have any pain along with it, definitely check in with your doctor. Just because you're bendy doesn't mean you need to let it break you.