In a 'normal' body, ligaments (which are the tissues that connect bones to each other) are naturally tight in such a way that the joints are restricted to 'normal' ranges of motion. This creates normal joint stability. If muscular control does not compensate for ligamentous laxity, joint instability may result.
The trait is almost certainly hereditary, and is usually something the affected person would just be aware of, rather than a serious medical condition. However, if there is widespread laxity of other connective tissue, then this may be a sign of Ehlers-Danlos syndrome.
There are some advantages to having lax ligaments, and joints that often have a wider range of movement - double jointed people almost by definition have overly lax ligaments.
Someone with ligamentous laxity, by definition, has loose ligaments. Unlike other, more pervasive diseases, the diagnosis does not require the presence of loose tendons, muscles or blood vessels, hyperlax skin or other connective tissue problems.
In The Feet: Those who have loose ligaments in the legs and feet often mistakenly assume that they have flat feet. While their feet have an arch when not supporting weight, when stood upon, the arch will flatten. This is because the loose ligaments can not support the arch in the way that they should. This can make walking and standing painful and tiring. Pain will usually occur in the feet and lower legs, but can also spread to the back due to abnormal standing and walking habits. Wearing shoes that have good arch support can help minimize the discomfort. The root problem, however, won’t get any worse from wearing shoes without arch support- one will simply experience more temporary discomfort.
Ligamentous -- condition pertaining to the ligaments, laxity -- looseness thereof.
Pronunciation: Lig-a-men-tus lax-ity