There are two major types of AMC:
1. Amyoplasia (classic arthrogryposis): Multiple symmetric contractures occur in the limbs.
2. Distal arthrogryposis: The hands and feet are involved, but the large joints are spared.
Etiology
Any condition that impairs in utero movement for > 3 wk can result in AMC.
Causes may involve:
1. Physical limitation of movement (eg, due to uterine malformations, multiple gestations, or oligohydramnios)
2. Maternal disorders (eg, multiple sclerosis, impaired uterine vascularity)
3. Fetal disorders (eg, neuropathies; myopathies, including muscular dystrophies; connective tissue abnormalities; impaired fetal vascularity; anterior horn cell disease)
4. More than 35 specific genetic disorders (eg, spinal muscular atrophy type I, trisomy 18) have been linked to AMC.
Symptoms and Signs:
Deformities are prominent at birth. AMC is not progressive; however, the condition that causes it (eg, muscular dystrophy) may be. Affected joints are contracted in flexion or extension. In classic AMC, shoulders are sloped, adducted, and internally rotated; the elbows are extended; and the wrists and digits are flexed. Hips may be dislocated and are usually slightly flexed. Knees are extended; feet are often in the equinovarus position. Leg muscles are usually hypoplastic, and limbs tend to be tubular and featureless. Soft-tissue webbing sometimes occurs over ventral aspects of the flexed joints. The spine may be scoliotic. Except for slenderness of the long bones, the skeleton appears normal on x-rays. Physical disabilities may be severe. As noted, some children may have primary CNS dysfunction, but intelligence is usually unimpaired.
Endotracheal intubation during surgery may be difficult because children have small immobile jaws. Other abnormalities that rarely accompany arthrogryposis include microcephaly, cleft palate, cryptorchidism, and cardiac and urinary tract abnormalities.
Diagnosis:
Evaluation should include a thorough assessment for associated abnormalities.
Electromyography and muscle biopsy are useful to diagnose neuropathic and myopathic disorders.
In classic AMC, muscle biopsy typically shows amyoplasia, with fatty and fibrous replacement of tissues.
Treatment:
1. Joint manipulation and casting
2. Sometimes surgical procedures
3. Early orthopedic and physical therapy evaluations are indicated.
4. Joint manipulation and casting during the first few months of life may produce considerable improvement.
5. Orthotics may help.
6. Surgery may be needed later to align the angle of ankylosis, but mobility is rarely enhanced.
7. Muscle transfers (eg, surgically moving the triceps so that it can flex the elbow) may improve function.
Many children do remarkably well; two thirds are ambulatory after treatment.
