What causes infant scoliosis?

Variety. Could be congenital scoliosis (malformations of parts of the spine), resulting in abnormal growth. Alternatively, certain syndromes result in scoliosis in addition to other medical issues which need to be identified, worked up and treated. A variety of neuromuscular problems can also be associated.
Problems in the womb. Congenital scoliosis (scoliosis at or shortly after birth) is due to a number of problems during development in the womb. The tissues forming the spine do not form or separate properly. Growth is abnormal, resulting in the abnormal curvature. Some will worsen with growth after birth, but others do not. A pediatric orthopedic or neurological surgeon specializing in scoliosis should be consulted.