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Amyoplasia is a condition characterized by a generalized lack in the newborn of muscular development and growth, with contracture and deformity at most joints. It is the most common form of arthrogryposis.
It is characterized by the four limbs being involved, and by the replacement of skeletal muscle by dense fibrous and adipose tissue. Studies involving amyoplasia have revealed similar findings of the muscle tissue due to various causes including that seen in sacral agenesis and amyotrophic lateral sclerosis. So amyoplasia may also include an intermediate common pathway, rather than the primary cause of the contractors.