One-stage posterior hemivertebral resection in the treatment of congenital scoliosis caused by hemimetameric shift

Congenital scoliosis results from defects formed during the embryologic development of the spinal vertebrae. Hemivertebra is a failure of vertebral formation carrying a risk of causing progressive scoliosis if it is fully segmented.1 When two hemivertebrae are present on the opposite sides of the spine and are separated by at least one normal vertebra, this condition then exemplifies a hemimetameric shift. The hemimetameric shift is often benign for progression, but it may also be problematic depending on the separation and the nature of the two hemivertebrae involved. If the two opposing hemivertebrae are close merely separated by one or two normal vertebrae, they tend to cause two small kinks in the spine and minimal cosmetic deformity. However, if the two hemivertebrae are in different regions of the spine, separate curves are then produced and the spine may become unbalanced, causing spinal decompensation and significant cosmetic deformity. In this article, we report one case for whom a hemimetameric shift was managed via a one-stage posterior hemivertebral resection. CASE REPORT A 15-year-old girl was admitted to our hospital in August 2004 complaining back asymmetry. Physical examination showed an elevation of the right scapula, with a tilting of the head to the left side. There were no trunk shifts and masses, dimples, or hairy patches on the patient’s back. A thorough evaluation of the patient did not reveal any other organ deformities except for the spinal deformity. Full-length X-ray examination of the spine showed a hemimetameric shift with two fully segmented hemivertebrae separately located at C7’ and T4’. The hemivertebrae caused three curves. The Cobb angle of the cervical curve (C5 to T3), caused by the C7’ hemivertebra (Fig. A), was 55° and the Cobb angle of the thoracic curve (T4 to T10), caused by the T4’ hemivertebra, was 73° (Fig. B). A secondary lumbar curve (T11 to L4) with a Cobb angle of 41° was created to balance the trunk (Fig. B). The Risser sign of the patient was 0 because she had been one year postmenarche. Myelography did not reveal any intraspinal anomalies. Computed tomography scans with three-dimensional reconstruction were performed to identify the shape and position of the hemivertebrae (Fig. C).Fig. A:: A fully segmented hemivertebra located at C7’ causing a cervical curve (C5—T3) of 55°. B: A fully segmented hemivertebra located at T4’ causing a 73° thoracic curve and a 41° lumbar curve. C: The 3D CT reconstruction showing a fully segmented C7’ hemivertebra. D: Postoperative X-ray film showing a 22° cervical curve with a correction rate of 42%. E: After the operation, the Cobb angle of the thoracic curve was 24° with a correction rate of 67%, and the secondary lumbar curve was 20° with a spontaneous correction rate of 51%.The progression of the curve and the poor cosmetic appearance indicated that an operation was necessary for this patient. The spine was exposed from C5 to T11. After the identification of the two hemivertebrae, the posterior elements of the hemivertebrae (the lamina with the transverse process in T4’ or the lateral mass in C7’, the facet joint, and the posterior of the pedicle) were removed. The spinal cord and the nerve roots around the hemivertebrae were identified. After the resection of the posterior elements of the hemivertebrae, its lateral and anterior parts were exposed; the excision of the hemivertebrae was performed by means of an “eggshell” procedure using a burr. After the hemivertebrae were decancellated, their walls were carefully removed with a Kerrison rongeur. Then the discs adjacent to the hemivertebrae were removed, and the vertebral end plates were debrided from to the bleeding bone. To achieve a complete osteotomy, the facet of the concave side was excised. Pedicle screws and lateral mass screws were separately placed at C5, C6, T1, T3, T5, T7, T8, T10. A rod (SummitTM, DePuy AcroMed)) was used to correct the deformity. A compression force was applied on the convex side until the gap resulting from the resection closed completely. An autologous bone graft was morselized and placed loosely in the space of the adjacent vertebral body. After the posterior elements of C5 to T10 were decorticalized, a bone graft was performed for spinal fusion. The patient’s recovery was quick and she was allowed to walk with a brace on the 5th day after the operation. In addition, there were neither neurological complications nor infections. Postoperative X-ray films of the spine were obtained one week after the operation. The Cobb angle of the cervical curve was 22° with a correction rate of 42% (Fig. D). The Cobb angle of the thoracic curve was 24° with a correction rate of 67%. The Cobb angle of the secondary lumbar curve was 20° with a spon- taneous correction rate of 51% (Fig. E). The trunk of the patient was balanced and the tilt of the head was adjusted. Follow-up X-ray film was obtained eighteen months after the operation. The patient maintained the balanced spine, and the correction did not revert. DISCUSSION Hemivertebra resection is an ideal method for the treatment of patients with a fully segmented hemivertebra, especially in cases where in situ fusion or hemiepiphyseodesis will not result in a balanced spine. A good correction of the index curve through an hemivertebra resection would avoid the transformation of the adjacent secondary curves to structural curves. Thus, only by an early operation, which almost completely corrects the deformed part of the spine, can a normal growth of the unaffected parts of the spine be ensured. In this case, the two hemivertebrae located at C7’ and T4’ were excised one stage posteriorly, and the resulted two curves were corrected with a posterior pedicle screw system. Satisfactory results were achieved with the one stage posterior osteotomy. Since the secondary lumbar curve was 41° pre-operatively, the structural curve would result if the upper index curves were not corrected. The ideal method was to correct the two upper curves and to let the lumbar curve be corrected spontaneously. After the correction of the two upper index curves, the lumbar secondary curve was corrected to a 20° with a spontaneous correction rate of 51%. So far, there have been several reports on hemivertebrae resection via a one-stage posterior approach.2,3 It seems to be a reliable procedure when performed on young children, but it is also associated with a higher risk of neurologic injury when the hemivertebra lies cephalad to the conus medullaris. In the reported case, the hemivertebrae was located at T4’ and C7’, and therefore, a high risk of neurological defect was present. Resection of the hemivertebra via its pedicle was the key for the successful operation. After the decancellation of the vertebra via its pedicle, the cortex of the body was excised with great care. When excising the posterior wall of the vertebra, bipolar and cotton compression is useful for dealing with epidural vein bleeding. Recently, Ruf et al4 reported excision of the hemivertebra in the cervical spine in three cases. In the three cases the cervical hemivertebrae located between C2 to C5 were excised via combining an anterior and posterior approach to prevent the risk of damaging the vertebral artery. Because there is no transverse foramen in C7, it may be the highest hemivertebra viable to be excised via a posterior one-stage operation. A simultaneous correction with instrumentation and resection of the hemivertebra located at C7 and the upper thoracic spine are feasible via a one-stage posterior operation. Risks resulting from neurological defects can be avoided through an “eggshell” operation and meticulous hemostasis. Surgery should be performed as early as possible to avert severe local deformities and to prevent secondary structural changes.

Topic: Scoliosis diagnosis and treatment
Subfield: Surgery
Field: Medicine
Domain: Health Sciences