Excision of a hemivertebra may be indicated when there is a hemivertebra causing progressive imbalance or curve progression in a growing child. The natural history of hemivertebra-induced curve progression is dependent on the anatomy of the congenital anomaly (8). A hemivertebra can be fully segmented with discs present above and below the abnormal vertebral body, partially segmented, or incarcerated (unsegmented). Because of the two convex growth plates present in a fully segmented hemivertebra, a fully segmented hemivertebra can progress approximately 2 degrees per year. This is compared to a partially segmented hemivertebra, which may progress by less than 1 degree per year (8). A fully incarcerated or semisegmented hemivertebra may not cause progressive deformity and may be better observed or treated differently. In general, we perform this operation from ages 3 to 8. Below age 3, the bones are often so weak that it is difficult to have sufficient anchor purchase, and above age 8, the spine and surrounding structures become stiffer and the cord seems a little less amenable to radical change without loss of signals. Observation during these years to see if there is progression and if surgery is needed or not is reasonable. Posterior element anomalies may differ from the vertebral bodies and may influence deformity behavior (9). Balanced deformities (hemimetameric shift) that result from hemivertebrae at different levels but opposite sides of the spine may not progress as the growth potential is similar on both sides of the curve. Hemivertebrae in the thoracolumbar, lumbar, and lumbosacral regions of the spine commonly cause progressive deformity above and below and are often an indication for early surgical treatment.

In general, hemivertebra resection should completely correct the patient’s local deformity in the coronal and sagittal plane. If the deformity involves a long section of the spine in a very young child, consideration should be given to growth-oriented treatments, such as a vertical expandable prosthetic titanium rib (VEPTR) or growing rods or Shilla. Patients between the ages of 3 and 5 years may be the best age for posterior-only hemivertebra excision. At this ideal age, vertebral size and strength are well enough developed to provide meaningful pedicle screw fixation and there is enough bony surface available to obtain reliable fusion. These children also represent minimal anesthetic risk. Consider earlier intervention in larger children or if the deformity is worsening rapidly or later if the child is small. The procedure can be performed on younger children, but spinal anchor fixation will be less secure and more postoperative external immobilization such as a body cast or brace will be needed. The procedure can be performed in older children easily, but the secondary deformities above and below may correct less well. Manipulation of the dura and contents is less well tolerated with advancing age, and the risk of neurologic injury may be greater above age 5 (10). Concern has been expressed about early circumferential fusion and the creation of iatrogenic canal stenosis; operating after the age of 18 months probably makes stenosis unlikely. If supplemental fixation in the form of a body cast is needed, children of this age can tolerate periods of immobilization and can still be carried fairly easily by parents.