What is Arthrogryposis Multiplex Congenita (AMC)?
Over 260 babies are born with arthrogryposis in the UK each year
Arthrogryposis is considered a rare and unusual condition which has been seen in art and literature for centuries. As different types of the condition became known, it began to be used as a clinical sign, or general category, leading to it to become a ‘description’ rather than a straight forward diagnosis.
The word Arthrogryposis literally means curved joint, implying that it is fixed or stuck in the curved position.
Arthrogryposis multiplex congenita put simply means curved joints in several areas of the body at birth.
Anything that prevents normal movement of a baby in the womb will lead to a contracture, where a joint does not have a full range of movement. The earlier in development, and longer there is a limitation of movement the more severe the contracture(s) is likely to be at birth.
Arthrogryposis is not a problem in the formation of the joint or limb, but is associated with the development of extra connective tissue around the joint and occurs after 8 to 10 weeks in the pregnancy. This extra connective tissue fixes a joint in place and severely limits its movement leading to the tendons around the affected joint not to stretch to their normal length making joint movement after birth even more difficult. However, when a limitation of movement occurs for several months, there also tends to be a lack of growth in a limb that can make the severity of the contracture even more intense.
Why does it happen?
There seems to be six problems which can affect the development of the joint and therefore cause fixation. These are:
- Abnormalities of Connective Tissue – here the tendons, bones, joint or joint lining, develop in such a way that normal movement cannot occur in the womb
- Limitation of Space or Restriction of Movement Within the Uterus – in certain situations there is limited room within the uterus such as with multiple births. In other cases there may be a lack of the normal level of amniotic fluid or the mother may have an abnormal shape to the womb that does not allow the baby to move freely – any compression can cause limitation of movement and secondary contractures.
- Abnormalities of the Muscle Structure or Function – known as myopathic processes this is where the muscles fail to form or do develop but do not function properly. The actual cause of this is unknown but it is suspected to include muscle disease (such as congenital muscular dystrophies) or where the muscles do not have enough energy to function normally.
- Abnormalities of the Nerves that Connect to the Muscles – called neuropathic processes this is where the nerves fail to form, mature or to function properly leading to a very severe lack of movement and often accompanies structural abnormalities.
- Vascular Compromise Leading to Loss of Neurons – this is where there is a problem with the blood circulating normally which then fails to nourish the nerves leading to the muscles or the bones that make up the joint.
- Maternal Illness – a number of maternal metabolic disorders and maternal illness have been associated with the presence of multiple congenital contractures in the baby
Incidence of Arthrogryposis
Arthrogryposis is relatively rare it is estimated to occur once in every 3,000 live births*.
However, many types of specific congenital contractures in a particular body area such as clubfoot or dislocate hips, are much more common – at least one in every 200 babies are born with some form of congenital contracture or stiff joint.
The rates of congenital contractures in the newborn are:
- Clubfoot - 1:5000
- Congenital dislocated hips - 1:2000-1:5000
- Multiple contractures - 1:3000
- All congenital contractures - 1:100-1:25
* (Source: Arthrogryposis A Text Atlas Edited by Lynn T. Staheli MD, Judith G Hall MD, Kenneth M Jaffe MD, Diane O Paholke BS. Published by Cambridge University Press and available at www.global-help.org)