The origin of prenatal and postnatal deformities.

Deformities are abnormalities of shape or form caused by abnormal or imbalanced mechanical forces. In prenatal deformation, most infants are intrinsically normal and the deformation results from extrinsic constraining forces. Most prenatal deformities will resolve spontaneously or with the application of counteracting forces. In contrast, postnatal deformities result from either extrinsic pathologic processes, affecting the bones, nervous system, or muscle and resulting in the application of abnormal forces to bone, or normal forces acting on intrinsic diseases of bone. While many postnatal deformities can be contained or corrected by the application of counteracting forces, aggressive physical therapy, casting, or surgery is often required for correction.