The hinge is like a joint, and the doorstop prevents the door from swinging too far and damaging the wall. Likewise, a joint with supporting structures that are loose or stretched will allow extra movement past the normal range of motion. This hyperextension can cause brief discomfort, swelling or pain in that area. The joint may partially dislocate because of the loose supportive ligaments and joint structures. The frequency of BHJS varies with sex, age and ethnic background.
Younger children tend to have more pain complaints.
Teen-agers may have fewer symptoms because their muscles and joints tend to become tighter and stronger as they become older, and because they better understand the relationship between increased activity and discomfort. When large groups of school children are tested, BHJS is found in 7 percent to 40 percent of them. Between 8 percent and 11 percent of these children have hypermobility that can lead to pain after activities or at night. No one knows why some children develop discomfort, while others with equally hypermobile joints do not have pain or swelling. There is often a family history of loose-jointedness.