Hypermobility joint syndrome (HJS) means your joints are “looser” than normal. It’s typically referred to as being double jointed.  It is a common joint or muscle problem in children and young adults, and is one of many connective tissue disorders.

Formerly known as benign hypermobility joint syndrome (BHJS), the condition can cause pain or discomfort after exercise. It’s usually not part of any disease.

Children or young adults with hypermobility have joint pain.

The pain is more common in the legs, such as the calf or thigh muscles. It most often involves large joints such as the knees or elbows. But it can involve any joint.

Some people also have mild swelling in the affected joints, especially during the late afternoon, at night, or after exercise or activity. That swelling may come and go within hours.

Other symptoms may include joint dislocation, thin skin, drooping eyelids, hernia, and varicose veins. 

Girls’ joints tend to be more mobile (looser) than those in boys of the same age. Younger children tend to report more pain. Teens may have fewer symptoms because their muscles and joints become tighter and stronger as they get older.

HJS seems to happen more often in Asian-American children than in Caucasian children, and it is least common in African-American children. The reasons for that aren’t clear.

When large groups of schoolchildren are tested, as many as 40% have the syndrome. About 10% of these children have hypermobility that can lead to pain after activities or at night. No one knows why some children feel that discomfort, while others with equally loose joints don’t have pain or swelling.

Loose joints run in families.

Simple tests show whether a child has a greater range of motion in their joints than normal. Doctors use several specific mobility tests, including:

Since the symptoms of hypermobility can sometimes mimic arthritis, you may need to get lab tests to make sure your child doesn’t have a more serious disorder (such as juvenile arthritis or other inflammatory conditions). In rare cases, you may need to get X-rays.