Amyoplasia is a relatively common form of arthrogryposis. It is also known as classic arthrogryposis. Its incidence is approximately one in 10,000 births. With treatment, longevity seems to be relatively unaffected.
It does not seem to be inherited. The pathogenesis is intrauterine hypoxia with damage to the anterior horn cells in the spinal cord of the child. This is thought to lead to relative hypokinetic limbs with subsequent secondary soft tissue contractures around joints.
Clinical features are usually symmetrical. The upper limbs often have a characteristic position with adduction and internal rotation at the shoulder, elbow extension, forearm pronation, wrist flexed and ulnarly deviated. The thumb may be flexed into the palm. The digits are flexed and stiff. In the lower limb, the hips are flexed and externally rotated. Occasionally, they may be subluxed or dislocated. Frequently, talipes equinovarus is present.
Other systemic features can include waxy skin without skin creases, little subcutaneous tissue, muscle wasting and midline facial haemangioma. Intelligence is normal.
The treatment of amyoplasia is adapted to the individual child's deficits within a multidisciplinary team setting. Options include splintage and surgical correction of contractures as detailed in the section on arthrogryposis.
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