INTRODUCTION

Positional deformations are abnormalities that are mechanically produced by alterations of the normal fetal environment, which restrict fetal movement and/or cause significant fetal compression [1]. Deformations of the extremities occur frequently because fetal movement is required for normal musculoskeletal development.

Birth deformations can be divided into the following presentations:

• Craniofacial abnormalities include scaphocephaly, plagiocephaly, mandibular asymmetry, flattened facies, deviated nasal septum, ear abnormalities, and craniosynostosis. (See "Overview of craniosynostosis", section on 'Categorization of cranial deformities'.)
• Congenital torticollis (see "Congenital muscular torticollis")
• Congenital scoliosis
• Lower extremity abnormalities including metatarsus adductus, positional calcaneovalgus feet, positional clubfoot, internal and external tibial torsion, and physiologic genu varum

The majority of deformations are due to foot and leg abnormalities, which are reviewed here. Developmental dysplasia of the hips, which is also associated with factors that restrict fetal movement, is discussed in greater detail separately. (See "Epidemiology and pathogenesis of developmental dysplasia of the hip" and "Clinical features and diagnosis of developmental dysplasia of the hip" and "Treatment and outcome of developmental dysplasia of the hip".)

ETIOLOGY

Deformations are caused by problems that are intrinsic and extrinsic to the fetus. Infants with deformations caused by extrinsic causes are generally otherwise healthy. Those with deformations due to intrinsic factors are at increased risk for other fetal abnormalities (eg, renal disease or central nervous system disorder).