Joint hypermobility - Causes 

Causes of joint hypermobility 

There are four factors that may contribute to joint hypermobility.

These are:

  • the shape of the ends of your bones
  • the structure of your collagen (a type of protein found in some types of tissue)
  • muscle tone
  • proprioception – sensing your body’s position and movements

These are explained in more detail below.

Shape of the bone ends

A joint is the junction between two bones. The shape of the bones determines how far you can move your limbs. For example, your limbs will be more flexible if the socket that the bone moves around in, such as the shoulder or hip socket, is shallow. A shallow socket will allow more movement in a joint.

Collagen structure

Collagen is a type of protein found throughout your body – for example, in skin and ligaments. Ligaments are tough bands of connective tissue (fibres that support other tissues and organs in your body) that link two bones together at a joint. They strengthen the joint and limit its movement in certain directions.

If the structure of your collagen is altered, it may not be as strong, and the tissues that contain collagen will be fragile. This can lead to weakened or easily stretched ligaments. All joints can be affected, particularly your knees and thumbs.

Changes in the structure of your collagen are likely to be caused by changes to your genes. Genes are single units of genetic material that you inherit from your parents. They contain genetic instructions that tell your body how to work. If the genetic instructions within the genes change, it can alter your collagen.

There may be several genes that affect the structure of collagen. Read more about how genes change and are inherited.

Hormones also appear to play a role in joint hypermobility because the female hormone, oestrogen, increases flexibility, probably by affecting collagen. Women may find that they are more supple before a period and less supple after the menopause (when a woman’s monthly periods stop).

Muscle tone

Children with joint hypermobility may have a degree of hypotonia (low muscle tone). This is more commonly seen in children with autistic spectrum disorders (developmental disorders) and chromosomal abnormalities, such as Down’s syndrome. Down's syndrome affects physical development and causes learning difficulties.

Sense of joint movement

You should be able to sense the position and movement of your joints. For example, even with your eyes shut you should know whether your arm is bent or straight. The medical term for this sense is proprioception.

However, if you have an abnormal sense of joint movement, you may not be able to sense when a joint is overstretched, so you will have a wider range of movement.

Other conditions

Joint hypermobility can be part of a more serious underlying condition. These are often hereditary (inherited) conditions which parents pass to their children. Some conditions that can cause symptoms of joint hypermobility are discussed below.

Osteogenesis imperfecta

Osteogenesis imperfecta is a rare condition sometimes known as brittle bone disease because it causes fragile bones. The condition can also affect teeth and cause hearing loss. The most severe forms of osteogenesis imperfecta may affect 1 in 25,000 people.

Marfan syndrome

Marfan syndrome is a condition that affects the body's connective tissues. These provide support and structure to other tissue and organs. It can affect the:

  • blood vessels, causing damage to the heart 
  • skeleton, causing long, thin limbs 
  • eyes, causing the transparent lens at the front of the eye to fall into an abnormal position (lens dislocation)

Approximately 1 in 5,000 people have Marfan syndrome.

Ehlers-Danlos syndrome

It is estimated that Ehlers-Danlos syndrome affects between 1 or 2 people in every 10,000.

Like Marfan syndrome, Ehlers-Danlos syndrome also affects connective tissues, although different types of the syndrome cause slightly different symptoms. Ehlers-Danlos syndrome can cause:

  • easy bruising
  • stretchy skin 
  • poor wound healing – leading to scars 
  • blue sclerae (white part of the eyes)

There are several different types of Ehlers-Danlos syndrome. Ehlers-Danlos syndrome type III, also called Ehlers-Danlos syndrome hypermobility type, is the same as joint hypermobility syndrome. 

It is important to identify the correct type of Ehlers-Danlos syndrome because some types (particularly type IV) carry an increased risk of burst blood vessels or other organs.

If you have Ehlers-Danlos syndrome type IV, you may be at increased risk of conditions such as strokes, or of developing a problem with your womb (uterus) if you are pregnant.


Page last reviewed: 10/09/2012

Next review due: 10/09/2014

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