Semi-segmented lumbar supernumerary hemivertebra resection in congenital scoliosis: a case report

Abstract

Background

Congenital scoliosis with progressive potential is a controversial subject in early-onset spinal deformities. The presence of a hemivertebra may produce severe spinal deformities. The evolution of a scoliotic curve in these cases is unpredictable and requires careful follow-up dependent on multiple variables, such as the location of the hemivertebra, the age of the patient at the time of diagnosis, and the degree of deformity already present in both sagittal and frontal planes. A segmented hemivertebra is an obvious cause of spinal deformity owing to its high progressive potential. A semi-segmented hemivertebra may induce severe deformities and surgery may be required, depending on the patients’ age, current deformity, and progressive potential. The age of 1.5–6 years is ideal to obtain an excellent surgical result. Prophylaxis of a predicted severe scoliotic curve owing to a semi-segmented hemivertebra requires a strategic surgical approach. While there are multiple surgical treatment options available nowadays, the current gold standard is the resection of the hemivertebra via a single posterior approach with limited fusion.

Case description

A 5-year-old Caucasian male child with congenital scoliosis owing to a semi-segmented hemivertebra at the thoracolumbar junction and a synchondrotic vertebral body bridge below the hemivertebra. The particularity of the hemivertebra consisted in the fact that it involved the L1 thoracolumbar transition area. The architecture of the upper part of the deformity resembled a T12-like deformity while the lower part was L1-like. Hemivertebra resection was performed by posterior approach and a short segmental fusion. The complete resection of the hemivertebra corrected the scoliotic curve and improved spinal balance. The patient was allowed to ambulate independently 3 days postoperatively while wearing a protective brace. Unrestricted daily activity was permitted 3 months after surgery. No complications were noticed until now.

Conclusion

Extensive clinical and imaging examination of the congenital malformation should be performed in all cases of congenital scoliosis owing to semi-segmented hemivertebra, especially if surgery will be performed. Proper diagnosis, age at surgery, and appropriate surgical technique ensure good results. Establishing which part of the involved spinal segment, including the semi-segmented hemivertebra, must be resected is essential to obtain a good correction with the shortest possible spinal fixation.

Background

Congenital scoliosis represents a special spinal pathology in children owing to the presence of spinal deformities starting with intrauterine life. Congenital scoliosis is a distinct part of early-onset scoliosis. Hemivertebra represents a formation defect owing to the absence of half of a vertebral body. It represents the most common cause of congenital scoliosis. This deformity is classified as a rare disease (3 cases per 10,000 newborns) and may present progressive potential with accelerated worsening of the scoliotic curve. Diagnosis is possible early in intrauterine life using ultrasonography [1]. There is a long period of evolution during the child’s growth until skeletal maturity is reached. For these reasons congenital scoliosis is a particular problem among pediatric spinal pathologies. The goal of all early-onset scoliosis treatment is to obtain a spine long enough to allow the development of all vital organs. Ideally, the final goal of the treatment is to obtain a spine as straight as possible in the frontal plane while preserving the normal sagittal curves. The “ideal” surgical cases of congenital scoliosis are represented by single-segmented hemivertebrae (simple solitary, unison). Segmented hemivertebrae may present a high progressive potential requiring early surgical treatment. Semi-segmented hemivertebrae, depending on factors, such as location (thoracolumbar, lumbosacral, or cervicothoracic transition zones) and size, may lead to significant imbalances of the spine owing to short arc curves and consecutive decompensation of the adjacent spinal segments [2]. Multiple methods of correction and control of scoliotic curves in early-onset cases are available to prevent a severe deformity of the spine without significantly affecting spinal growth. Growth phases, especially the accelerated ones, are typically managed safely until full skeletal maturity is attained. Different surgical techniques have been standardized and improved lately to be as friendly as possible to the growth and development of the spine–thorax–lung axis [3]. Resection of the hemivertebra by a single posterior approach and minimal instrumentation has become the ideal method of surgical treatment in congenital scoliosis owing to hemivertebrae [4].

The resection of the hemivertebra according to Ruf and Harms (2002) via a single posterior approach and minimal segmental instrumentation is nowadays the surgical gold standard. This technique presents the advantage of a single posterior approach. It is limited to the level of the hemivertebra and the adjacent vertebrae, resulting in minimal fusion that insignificantly affects the growth in height of the vertebral column. This technique allows both the complete excision of the vertebral malformation represented by the hemivertebra, and a safe and minimal fixation by means of transpedicular screws or laminar hooks if pedicles cannot be instrumented. Magnetic resonance imaging (MRI), computed tomography (CT), and three-dimensional CT (3D-CT) are very important in establishing the surgical planning (Fig. 1). The differential diagnosis of a segmented or a semi-segmented hemivertebra are made by CT and MRI scans. X-rays are inconclusive in many cases. The significance of CT and MRI scans relies in their ability to detect potential associated spinal and medullary malformations that cannot be seen on X-rays (bony or fibrous diastematomyelia, syringomyelia, and so on). The architecture of the hemivertebra and the relation to neighboring structures may be accurately established [5].

Fig. 1

Imaging investigations highlight a T12 semi-segmented hemivertebra and a junctional kyphosis with a short arc

The dimensions of the components of the adjacent vertebrae to be instrumented (diameter, length and direction of the pedicles) are determined by spinal CT-scan. CT helps establish the correspondence of the malformation at the anterior level (vertebral bodies) related to the posterior part of the spine (vertebral laminae). This may discover cases of discordance between anterior and posterior elements, which may change the planning related to the approach and instrumentation [6, 7]. The surgical procedure is ideally performed starting at the age of 1.5–6 years [8, 9]. Real-time navigation highlights the certainty of the complete excision of the hemivertebra, confirming what the surgeon perceives visually and by palpation.

The detailed Ruf and Harms technique consists of:

• 1. The patient is placed in prone position and intraoperative neuromonitoring sensors are applied. The hemivertebra is fluoroscopically identified.

• 2. The incision and the approach are centered on the midline (spinous apophyses) and only the adjacent vertebrae to be instrumented are exposed by a strict exposure. The lamina of the hemivertebra to be excised is exposed and the sites of the transpedicular screws are prepared (Fig. 2A).

• 3. The transpedicular screws are inserted at the level of the adjacent vertebrae. On the convex side (opposite to the hemivertebra) a provisional longitudinal rod is placed to ensure the stability of the spine during the resection of the hemivertebra.

• 4. The rib corresponding to the hemivertebra is identified and partially resected by costotomy and costo-transverse and costo-vertebral disarticulation to gain access to the lateral part of the hemivertebra. The hemivertebral pedicle is identified after detaching the hemivertebral lamina and the hemivertebra and the adjacent intervertebral discs are completely excised with a curette. (Fig. 2B). This maneuver is likely to cause bleeding and hemostatic materials should be used to ensure a clearly visible operative field. The corresponding nerve roots are protected. The last component to be resected is the posterior wall of the hemivertebra. Special caution is required to avoid injuries of the spinal cord. The complete excision of the hemivertebra is confirmed visually and radiologically.

• 5. Two final longitudinal rods are connected to inserted pedicle screws. The correction of the scoliotic curvature is obtained by compression of the convex side (closing the space from where the hemivertebra was excised) and in some cases by minimal distraction on the concave side. The bone autograft resulting from the rib and hemivertebra resection is applied in the gap of the hemivertebral resection and around the screw insertion area to obtain a firm spinal fusion (Fig. 2C).

Fig. 2

Preoperative identification of the hemivertebra. Preparing of the insertion points of the transpedicular screws (A). Insertion of transpedicular screws and fixation of the spine with a provisional rod on the concavity. Identification of the hemilamina corresponding to the hemivertebra. Excision of the hemivertebra and radiological check (B). Mobility check of the spine and the efficiency of the transpedicular screws by compression maneuvers. Final implant and radiological verification of correction (C)

X-rays of the spine will be performed postoperatively to visualize the proper fixation and balance of the spine. In older children there is no need for a spinal brace if adequate fixation is obtained (however, a brace is indicated for safety in children under the age of 6 years for a period of 3–6 months) and mobilization may be carried out early.

Fractures of the pedicles in the excision area of the hemivertebra are described in about 10% of cases (although intraoperatively the assembly may be stable during compression maneuvers and the “pull-out” test). Extension of the implant one level lower without subperiosteal dissection of the additional corresponding area is a viable option if a pedicle fracture is noticed during surgery. A third rod (supra- and sublaminar hook in the form of a compacting claw) may be applied to stabilize the adjacent vertebrae (Fig. 3).

Fig. 3

Postoperative fracture of a distal pedicle and extension of the implant with a distal level and consolidation with a third rod as a claw with two laminar hooks

Case presentation

We present a case of congenital scoliosis with supernumerary L1 semi-segmented hemivertebra in a 5-year-old Caucasian male child (Fig. 4). The child’s history was unremarkable, except for the parents noticing a slight shifting of the shoulders and the pelvis while standing at the age of 3 years. The Adams’ test (forward bending) showed minimal curvature of the spinous processes centered on the lower thoracic area. The spinal X-rays identified a scoliotic curve with a L1 supernumerary hemivertebra. CT and MRI exams revealed congenital scoliosis with a left L1 supernumerary semi-segmented hemivertebra and a left L5 megapophysis articulated to the sacral wing. All other biological and functional exams were within normal limits. No other visceral malformations were noticed. The child presented no physical impairment.

Fig. 4

Congenital scoliosis owing to a supernumerary left L1 semi-segmented hemivertebra and left L5 megapophysis articulated to the sacral wing. The true supernumerary semi-segmented hemivertebra could be the upper or the lower component (blue arrows). The left L1 component of the semi-segmented supernumerary hemivertebra appears as a T12 vertebra in the upper part and as a L1 in the lower part (red arrows). An eccentric anterior synchondrotic bridge is noticed between L1 and L2

CT and MRI exams highlighted a L1 vertebra containing the supernumerary hemivertebra with the following aspects: the right side of the L1 vertebra presented the typical aspect of a lumbar vertebra. The left side (which included the hemivertebra) presented as a T12-like vertebra in the upper part and a L1-like vertebra in the lower part. Which is the real hemivertebra, the upper or the lower part of the L1? The patient also had a left L5 transverse megapophysis articulated to the sacral wing with no imbalance.

The scoliotic curve was not significant (approx. 20° Cobb angle), but calculating the progressive potential (lumbar area, and eccentric underlying synchondrotic bridge on the same side as the hemivertebra) the probable progression might be 2.5–3°/year. Such a scoliotic curve could theoretically reach a 50° Cobb angle at skeletal maturity meaning a definite surgical indication. The excision of the hemivertebra becomes logical according to this assumption [10]. Other surgical options would neither correct the scoliotic curvature nor the anterior vertebral wedging, with the consequent risk of kyphosis in the transition area and degenerative phenomenon. The only procedure that directly addresses the malformation is hemivertebra resection. All other available techniques may at best control the curve, but the vertebral malformation remains in place. Therefore, the indication for surgical intervention was justified owing to the patient’s age (in the ideal interval), anterior wedging, no vertebral structural changes, and pedicles of reasonable size. The widening of the medullary canal in the hemivertebral area may lead to narrower pedicles consecutive to the changes induced by the progression of the curvature, just as in concavities of idiopathic scoliosis.

Logically the hemivertebra is the upper part of the left L1 and this one should be resected. A synchondrotic bridge between the lower left part of L1 and L2 was also noticed. It seemed obvious to resect the upper part, but this approach would have left the synchondrotic bridge in place, leading to degenerative phenomena and worsening of the kyphoscoliotic area below the fusion area. We therefore decided to resect the lower part of the left L1 and to fuse L1 and L2.

Surgery consisted of resection of the lower component of the supernumerary L1 semi-segmented hemivertebra. The extension of the implant to L3 was considered for safety reasons, but without deperiosting distal to L2 so that the two L3 screws may be removed once solid fusion is established. A third rod was used in the form of a L1–L2 laminar claw for solid fixation. Distraction was performed between L2 and L3 to remove pressure from the intervertebral disc (Fig. 5). The instrumentation between L2 and L3 may be removed a few months after surgery leaving the intact intervertebral joints mobile.

Fig. 5

Excision of the L1 supernumerary semi-segmented hemivertebra (lower component). The resection area is delimited with a chisel after the partial excision of the semi-segmented hemivertebra. X-ray check-up in standing position

The child was able to walk independently, wearing a brace for safety, 3 days after surgery. We noticed satisfactory spinal correction with no frontal or sagittal imbalance and proper fixation 6 weeks postoperatively. The brace was discontinued 6 weeks after surgery. No physical impairment was noticed. The child was allowed unrestricted daily activities 3 months after surgery. Follow-up will be continued yearly until skeletal maturity.

Discussion

This case presents the surgical treatment of a congenital scoliosis with a semi-segmented supernumerary hemivertebra located in the T12–L1 transition area. Certain cases require surgery to avoid worsening of the scoliotic curve and accompanying complications. The evolution of these patients is unpredictable even if a very good initial surgical correction has been achieved. Additional vertebral malformations could explain the possible appearance of secondary curves, especially during accelerated growth periods.

A dilemma is the identification of the semi-segmented hemivertebra to be resected (conceptually simplified, the proximal part or the distal part of the vertebral malformation?), especially in the thoracolumbar transition area where vertebral architecture changes. A detailed CT investigation may reveal more detailed vertebral changes that raise fundamental approach problems. Apparently without practical importance, these changes may influence the intraoperative and long-term postoperative result considering the unpredictable evolution in the context of congenital scoliosis, including those operated successfully [11]. Excision of a semi-segmented hemivertebra is more difficult and riskier to perform owing to the absence of an intervertebral disc, which functions as a good landmark. An osteotome is helpful to clearly delimit the resection area. The hemivertebra is linearly detached from the remaining vertebral component to reconstruct a “normal” vertebra. This maneuver is performed after the partial hemivertebral resection via curetting to allow the tipping with an osteotome of the remaining hemivertebra in the initially created space. It is recommended to use a third rod in the form of a laminar claw and/or to extend the implant without damaging the growth potential of these levels [12]. The implant is limited to a two to three or sometimes four vertebral levels. This approach does not require other subsequent surgical interventions compared with other techniques (growing rods or controlled growth guidance). Spinal growth will not be significantly affected [13]. A third rod as a claw better stabilizes the entire assembly in very young patients with partially cartilaginous vertebrae in which fixation on the posterior vertebral arch is stronger than screws [14]. The implant can be extended by one level for improved fixation, but without subperiosteal exposure, and without excising the interspinous ligaments and the intervertebral articular processes. The transpedicular screws do not affect the dimensions of the medullary canal [15].

Conclusion

Hemivertebra resection represents the most effective treatment (single intervention, limited fusion, and low morbidity compared with the anterior or combined approach). The advantage of this technique consists in whole hemivertebra excision by a minimal posterior approach. Proper diagnosis and surgical timing ensure the best results while the decision of which part of the semi-segmented hemivertebra is to be resected remains a question answered by careful examination of the malformation. This technique allows a rapid social reinsertion in daily activities and a significant improvement in quality of life. The results are not visible immediately, but in the long term. Complications, such as severe curves, spinal degenerative phenomena, and neurological problems, are avoided by correct surgical treatment. The limited fusion allows a quasi-normal increase in the size of the vertebral column respecting the spine–thorax–lung axis.