Arthrogryposis Multiplex Congenita (AMC)

What is arthrogryposis multiplex congenita (AMC)?

Arthrogryposis multiplex congenita (AMC) refers to the development of multiple joint contractures affecting two or more areas of the body prior to birth. A contracture occurs when a joint becomes permanently fixed in a bent or straightened position, which can impact the function and range of motion of the joint and may lead to muscle atrophy. AMC is not a specific diagnosis, but rather a physical symptom that can be associated with many different medical conditions. Two of the most common forms of AMC are amyoplasia and a group of genetic disorders called the distal arthrogryposes.

What are the symptoms of arthrogryposis multiplex congenita (AMC)?

The most common universal symptom of AMC is limited or absent movement around small and large joints (contractures). The muscles of the affected limbs may be underdeveloped (hypoplastic), resulting in a tube-shaped limb with a soft, doughy feeling. Soft tissue webbing may develop over the affected joints. In addition to joint abnormalities, other findings include:

Abnormally slender and fragile long bones of the arms and legs and cleft palate
Undescended testicles in males
Structural or functional abnormalities of the central nervous system

Additional symptoms associated with AMC are related to the underlying disorder that causes the condition in each individual. The specific symptoms and their severity can vary dramatically based upon the underlying cause. Amyoplasia is the most common form of AMC. Amyoplasia is a disorder characterized by multiple contractures of the joints. The shoulders may be internally rotated and drawn inward (adducted), the elbows are usually extended, and the wrists are usually flexed. In most affected individuals, the fingers are flexed and stiff. Affected individuals usually have severe clubfoot. The distal arthrogryposes are a specific subgroup of AMC. This subgroup is characterized by multiple congenital contractures. Common symptoms include contractures of two or more areas of the body, less involvement of the proximal joints (those joints closest to the center of the body), and highly variable expressivity, which means that specific symptoms vary greatly even among individuals with the same disorder and even in the same family. At least 10 different forms of distal arthrogryposis have been identified.

What causes arthrogryposis multiplex congenita (AMC)?

There are many causes of AMC, some of which are inherited. Before birth, four possibilities exist that limit joint movements:

Abnormal development of muscles
Inadequate room in the uterus for the baby
A malformed central nervous system and spinal cord
Tendons, joints, bones, and joint linings which did not mature correctly

The decrease in range of motion is also caused by extra tissue that has formed around the joint, prohibiting movement.

How is arthrogryposis multiplex congenita (AMC) diagnosed?

A diagnosis of AMC is made based upon identification of characteristic symptoms, a detailed patient history, and a thorough clinical evaluation. Specific tests to confirm diagnosis may include a muscle biopsy and electromyography.

What are the treatments for arthrogryposis multiplex congenita (AMC)?

The treatment of AMC is directed toward the specific findings that are apparent in each individual. Standard physical therapy, which can improve joint motion and avoid muscle atrophy in the newborn period is beneficial.