What causes joint hypermobility?
Four factors may affect whether or not you have hypermobile joints:
Weak or stretched ligaments – Ligaments are made up of several types of protein fibre, including elastin (which gives stretchiness) and collagen (which gives strength). Small changes in the chemical processes in your body can result in weakened collagen fibres and more elasticity in the ligaments that help to hold the joints together. This is likely to cause hypermobility in many joints. There's fairly strong evidence that hypermobility caused by abnormal collagen can be inherited. If one parent has this type of hypermobility then half of their children are likely to inherit it, though members of the same family may be affected differently.
The shape of your bones – If the socket part of the hip or shoulder joint is particularly shallow, the range of movement in the joint will be greater than usual and there'll also be a greater chance of dislocation. This is likely to affect a single joint or a small number of joints. It isn't a common cause of hypermobility but is likely to be inherited.
Muscle tone – The tone (or stiffness) of your muscles is controlled by your nervous system. The more relaxed your muscles are, the more movement you’ll have in your joints.
Sense of joint movement (proprioception) – Some people find it difficult to sense the position of a joint without being able to see it.