The hemivertebra could be an extra bone that started to form but didn't finish. Or it could be one of the regularly present bones that is missing half of its parts. The most likely cause of hemivertebrae is a lack of blood supply. Because it forms during the child's development in the womb and is present at birth, the condition is congenital.

A hemivertebra may not be a problem. But in some children, it can cause compression of the spinal cord. It changes the shape of the vertebral canal where the spinal cord passes. Pressure on the spinal cord or spinal nerves can cause serious neurologic problems.

Hemivertebra are also wedge-shaped. The unevenness of the spine from the extra, half-vertebra that is wedge-shaped can cause a change in the angle of the spine. Depending on the location, this may be a kyphosis, scoliosis, or lordosis. With kyphosis, the spine is curved forward when viewed from the side. Scoliosis refers to a C-shaped or S-shaped curve of the spine when viewed from the back. Lordosis is an excessive swayback position of the low back area.

Surgery to remove the bone is sometimes advised. This can be done safely and usually in one operation. The goal is to restore normal spinal alignment. Excellent long-term outcomes have been reported in studies.