Arthrogryposis refers to a joint that is in a fixed position. Arthrogryposis multiplex congenita is diagnosed when two or more joints in more than one limb are fixed from birth (Figure 151.1).

Figure 151.1.— Arthrogryposis multiplex congenita.

A joint becomes fixed in a given position because of unevenly impaired motility. Unevenly impaired joint motility results from segmental muscle weakness or hypotonia, or from a sustained asymmetrical posture. Segmental muscle weakness or hypotonia is due to an imbalance between agonistic and antagonistic muscles acting upon a joint. Sustained asymmetrical posture results from movement constraints that occur as a result of reduced uterine volume or cutaneous bands that restrict movements.