The hip is at risk as the fetal lower limb rotates medially. A dislocation at this time is termed teratologic. All elements of the hip joint develop abnormally. The hip muscles develop around the 18th gestational week. Neuromuscular problems at this time, such as myelodysplasia and arthrogryposis, also lead to teratologic dislocations. During the final 4 weeks of pregnancy, mechanical forces have a role. Conditions such as oligohydramnios or breech position predispose to DDH. Postnatally, infant positioning such as swaddling, combined with ligamentous laxity, also has a role before 1970, radiological examination of the hip was based on conventional radiography, and scintigraphy. Later, computed tomography (CT) and magnetic resonance (MR) imaging were introduced, but due to the deep location of the hip joint, ultrasound (US) examination has always had a relatively limited role in the assessment of hip pathologies.