What is Arthrogryposis Multiplex Congenita (AMC)?
Arthrogryposis Multiplex Congenita (AMC) is a term used to describe over 300 conditions that cause multiple curved joints in areas of the body at birth. It varies from person to person with the commonality being stiff joints and muscle weakness.
AMC is not a specific diagnosis but rather a clinical finding of permanent shortening of joints also referred to as non-progressive congenital contractures.
AMC is non-progressive meaning that the lack of movement, does not get worse as time goes by however, it is recommended that people affected seek advice to potentially prevent further impediments of the joints.
Occasionally AMC can also affect the central nervous system of which the survival rate can be low.
Causes of Arthrogryposis Multiplex Congenita (AMC)
Arthrogryposis Multiplex Congenita (AMC) is not a result of a problem in the formation of the joints, but rather with the development of the connective tissues around them that occurs after 8-10 weeks of pregnancy.
In AMC, this tissue fuses a joint in place, severely restricting movement in the areas affected which leads to the tendons around the affected joint being unable to stretch to their normal length. When there is limited movement for several months, this can also lead to joint contractures.
There are many causes of Arthrogryposis Multiplex Congenita (AMC) some of which are inherited. These are:
Abnormalities of connective tissue where the tendons, bones, joint or joint lining, develop in such a way that normal movement cannot occur in the womb.
Limited space or restricted movement in the womb 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.
Abnormalities of the muscle structure or function also known as myopathic processes this is where the muscles fail to form or do develop but do not function properly.
Abnormalities of the nerves that connect to the muscles also known as 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 illnesses have been associated with the presence of multiple congenital contractures in the baby.