All of my life, within my family, I have heard the term “double-jointed.” That’s because on my paternal grandmother’s side of the family, this rather rare characteristic ran in the family. It was passed down to my dad, then to me.
Being double-jointed doesn’t really mean you have two sets of joints. The proper name is hypermobility syndrome. A person with this syndrome looks like they can stretch a limb farther than they should be able to. Instead, it actually is the ability to stretch the ligaments and tendons around the joint that cause the hyperextension of the bone possible. The person can hyperextend the bone without the pain that a person without the syndrome would feel.
An example is someone who can easily touch their toes. In both my dad’s case and mine, we could/can lay our palms flat on the floor with absolutely no effort and no pain. Sometimes, this “double-jointedness” is due to shallow hip or shoulder sockets. People with this syndrome are often very limber and move very easily.
Often, as a person with hypermobility syndrome grows older, arthritis becomes present in the joints.