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Orthopaedic Advances

“Growth Friendly” Spine Surgery: Management Options for the Young Child With Scoliosis

Gomez, Jaime A. MD; Lee, Joseph K. MD; Kim, Paul D. MD; Roye, David P. MD; Vitale, Michael G. MD

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American Academy of Orthopaedic Surgeon: December 2011 - Volume 19 - Issue 12 - p 722-727
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Abstract

Because of both the dismal natural history of early onset scoliosis and the unfavorable effects of early fusion, clinicians who treat young children with scoliosis use a variety of surgical techniques in an attempt to avoid, delay, or limit spinal fusion. These “growth friendly” techniques and implants allow curve control and limit early spinal fusion. The growth rate of the spinal column varies bimodally with age, with the most rapid growth taking place from birth to age 2 years, and further rapid growth occurring again at adolescence. The volumetric growth of the thorax as a three-dimensional structure is of major importance; understanding has improved regarding the complex relationships between the structure and function of the spine, thorax, and lungs. Although the spine has a major effect on lung and thoracic cavity development, cross-sectional volume also depends on the growth of the ribs, both in length and the degree of rib obliquity. Thoracic volume increases to 30% of the adult size by 5 years of age and to only 50% of the adult size by 10 years of age.1,2 Thoracic volume can be limited by curve progression or by early fusion.3,4

Pehrsson et al5 noted a statistically significant increased risk of mortality related to respiratory failure in children with infantile or juvenile scoliosis compared with children with adolescent scoliosis. Vitale et al6 and others7 have demonstrated untoward effects of early fusion on pulmonary function. Avoidance of this iatrogenic thoracic insufficiency is a guiding principle of treatment in the young patient with scoliosis.8

Early Onset and Congenital Scoliosis

Early onset scoliosis is a heterogeneous condition. Prognosis and natural history vary widely depending on whether the etiology is congenital, idiopathic, syndromic, or neuromuscular.9 The natural history of congenital scoliosis is unpredictable, and patients require close follow-up. Those at highest risk of progression include young patients with a failure of segmentation, especially when accompanied by a contralateral unsegmented hemivertebra.10

Resection and/or early limited fusion may be the best option in cases of isolated anomalies that affect short spinal segments before progression and the development of compensatory curves.11 However, young patients with more complex, multisegment deformities may benefit from a growth-friendly approach.6,12,13 Although indications for surgical intervention vary,14 most surgeons prefer to intervene with a growth-friendly construct before rotation results in a windswept thorax, intrusion into the hemithorax, and subsequent restriction of pulmonary function.15

Management

Successful management of early onset scoliosis intends to improve or prevent progression of spinal deformity and chest wall constriction, avoid or limit early spinal fusion, and minimize surgical complications and negative effects of treatment on quality of life.

Casting techniques were commonly used for the treatment of scoliosis before the introduction of spinal instrumentation.16,17 Mehta18 reported extensive experience with serial casting in patients with infantile idiopathic scoliosis, which resulted in a resurgence of interest in this method. Curves with a rib vertebral angle difference >20° were considered to have a high propensity for progression and were serially casted every 8 to 16 weeks. In one study, 94 of 136 patients (69%) had full curve correction, with greater success in children treated before age 2 years.16 Principles of Mehta casting include the use of a specialized casting table, moderate traction, and emphasis on derotation of the thorax and spine.19 Skin complications have been reported, and attention to meticulous technique is essential.

Growth-friendly implants are used to control thoracic spinal deformity and minimize the adverse impact on growth and development of the spine and thorax. Skaggs et al20 have proposed a classification of growthfriendly implants that describes implants as distraction-based (ie, growth rods, vertical expandable prosthetic titanium rib [VEPTR; Synthes, West Chester, PA]), guidedgrowth (ie, Luque trolley, Shilla), and compression-based techniques (ie, tethers, staples).

In large curves, preoperative halo traction is sometimes used before instrumentation in an effort to decrease neurologic risk, obtain better correction, and improve pulmonary function before surgery.21 Recent publications have described the use of traction in early onset scoliosis for curves >80° and when associated with kyphosis before growth-friendly instrumentation.19

Distraction-based Implants

Distraction-based implants correct and maintain spinal deformity via spinal distraction, not unlike the manner in which the original Harrington rods functioned. These distraction-based implants can be attached to the spine, ribs, or pelvis depending on patient age, characteristics of the curve, and available bone stock. In our experience, proximal rib fixation is generally more appropriate in younger children in whom we are trying to avoid or delay spinal fusion and in whom spinal fixation is limited by an immature spine, in which implants may lead to complications. Traditional growth rods and the VEPTR provide similar options for the management of young children with scoliosis.

Although Bess et al22 and Akbarnia et al23 demonstrated increased curve correction and overall T1-S1 growth with frequent lengthening, more recent studies have demonstrated an increased risk of complications with each procedure as well as less length gained with each subsequent lengthening. Controversy exists regarding the optimum timing for implantation of a growth rod as well as optimum lengthening intervals.

Growing Rods

Originally described by Harrington and modified by Moe, the growing rod technique has undergone several modifications that allow for control of the deformity while minimizing complications. Although no absolute indications exist for the use of growing rods, generally accepted indications include significant remaining axial growth, progressive deformity >50°, and flexible spinal deformity.9,24–27 Typical results include those reported by Akbarnia et al,9 who reported on 23 children with progressive early onset scoliosis who underwent dual growing rod treatment. The Cobb angle improved from 82° preoperatively to 36° at time of fusion. T1-S1 length increased from an average of 23 cm preoperatively to 32.6 cm at the time of fusion. Complications occurred in 11 of 23 patients (48%). Innovations such as low profile designs, growing connectors, dual rod application, and the use of rib fixation and/or pedicle screws have enabled surgeons to control deformity. Allowing continued spinal column growth though these systems could benefit from further technological improvements; however, this is a challenge given the “orphan nature” of this small patient population (Figure 1).

Figure 1
Figure 1:
In an 8-year-old girl with tetralogy of Fallot with progressive thoracic scoliosis, the curve continued to progress despite the use of thoracolumbosacral orthosis bracing. A, Preoperative PA radiograph demonstrating a 65° thoracic curve. B, The patient underwent implantation of a growing rod distraction system. Immediate postoperative PA radiograph demonstrating a Cobb angle of 29°. C, PA radiograph made after 3-year follow-up demonstrating that curve correction is maintained after multiple lengthenings. The white arrow demonstrates axial lengthening along the growing rod.

Pedicle screws should be used with caution in the upper thoracic spine of the very young child; other types of proximal instrumentation (ie, hooks, rib cradles) should be considered instead. In our experience, when screws are used in the proximal thoracic spine of the young child, it is advisable to have at least four screws sharing load. Also, to avoid convergence, the starting point should be positioned on the medial edge of the pedicle aiming directly down the pedicle. This technique may prevent devastating neurologic complications if proximal control of the deformity is lost or if screws pull out posteriorly.

Pelvic fixation for growing rods includes sacral screws, iliac screws, or iliac hook fixation. Sponseller et al28 compared four different types of pelvic fixation in 36 children with progressive scoliosis, including iliac screws, iliac rods, S-rods, and sacral screws. At a follow-up of 40 months, iliac screws achieved statistically significantly better Cobb and pelvic obliquity correction than did sacral fixation (47% versus 29% and 66% versus 40%, respectively). However, there were five broken iliac screws, whereas the other fixation techniques had no breakage.

Vertical Expandable Prosthetic Titanium Rib

VEPTR placement was originally indicated for patients with rib fusions, but currently the VEPTR functions very much like the traditional growing rod. Compared with the growing rod, the VEPTR features circumferential rib anchors, telescopic lengthening allowing twice more lengthening, and a lengthening mechanism that allows expansion in the kyphotic segment of the thoracic spine, as opposed to axial connectors, which generally need to be placed at the thoracolumbar junction.

Several studies demonstrate the efficacy of the VEPTR in controlling curve magnitude and promoting spine growth (Figure 2). Campbell and Hell-Vocke29 reviewed 27 children with congenital scoliosis and fused ribs who underwent expansion thoracostomy and VEPTR insertion. At a mean follow-up of 5.7 years, scoliosis had decreased from a mean of 74° preoperatively to 49°. Mean thoracic spine growth per year was 0.80 cm. The presence of an unsegmented bar seemingly did not prevent spine growth; expansion thoracoplasty led to an average of 7.3% increase in length of the bar at a 4.2-year follow-up.29

Figure 2
Figure 2:
Vertical expandable prosthetic titanium rib (VEPTR [Synthes]) instrumentation in a 5-year-old girl with early onset scoliosis as well as congenital diaphragmatic hernia and rapid curve progression. Radiographs made following surgery to insert a bilateral rib-to-pelvis VEPTR, with a lengthening every 6 months, demonstrate adequate curve correction and spine growth. Clinically, the patient's lung function significantly improved, as well, at 2-year follow-up. A, Preoperative AP scoliosis radiograph. Lateral (B) and AP (C) scoliosis radiographs made 2 months postoperatively. D, AP scoliosis radiograph made 6 months postoperatively. E, AP scoliosis radiograph made 2 years postoperatively.

Complications are similar to those of traditional growing rods, including wound problems, rib fracture, and creeping fusion. Iliac S-hook migration has also been reported, and debate continues regarding the appropriate means of anchoring to the pelvis in growing constructs.30 Traditional growing rods are currently employed in a “physician directed” use, whereas the VEPTR has been FDA approved for the management of progressive scoliosis with “thoracic insufficiency” under a humanitarian device exemption.31

Limited data exist regarding the effect of distraction instrumentation on lung function, in part because of the difficulty in measuring pulmonary function in young children. Motoyama et al32 measured forced vital capacity in 10 children with thoracic insufficiency syndrome and scoliosis. At a mean follow-up of 33 months, forced vital capacity increased significantly, averaging 26.8% per year. Using hemoglobin as a surrogate marker for pulmonary function, Caubet et al33 reviewed hemoglobin levels in 138 children with early onset scoliosis preoperatively and at 6 to 24 months postoperatively follow ing VEPTR (n = 85) or growing rod (n = 58) insertion. These authors noted that 23% of children with early onset scoliosis had evidence of chronic hypoxia as measured by serum hemoglobin levels, with significant improvements noted after spinal distraction using the VEPTR.

Guided-growth Implants

The Luque trolley was a technique in which rods were attached to the spine using sublaminar wiring. Now largely of historical interest, this technique required extensive subperiosteal dissection, which increased the risk of inadvertent fusion and, thus, limited spine growth. Mardjetko et al34 retrospectively reviewed nine children treated with the Luque trolley system; all required revision surgery and had spontaneous fusion of the instrumented region.

The Shilla technique allows for apical curve control while allowing spine growth, without the need for frequent, planned subsequent surgeries.35 Apical pedicle screws are placed, effecting a limited fusion, while proximal and distal screws are placed under fluoroscopic guidance with the intention of avoiding fusion. The rods are fixed to the screws at the apex and can slide inside the screw head at the proximal and distal end. McCarthy et al35 demonstrated continued spine growth and no implant failure with the Shilla system in a goat model; however, significant facet arthrosis was also found. Although these implants are currently not available for clinical use, they will likely soon be available under a humanitarian device exemption.

Compression-based Implants

Vertebral body stapling is a new technique used for adolescent and juvenile idiopathic scoliosis. As predicted by the Hueter-Volkmann principle, increased pressure across a growth plate in the vertebral body slows growth. Although this phenomenon has been observed in experimental animal spine models,36 experience in the 1950s using stapling with large congenital curves was disappointing.37

More recently, flexible tethers attached to vertebral anchors have been used to modulate spinal growth. Use of tethers in animal models by Newton et al38 have demonstrated vertebral wedging, which could potentially correct scoliosis. Using a goat scoliosis model, Braun et al39 showed that flexible bone anchor/tethers can moderately correct deformity in the coronal plane but that this effect was lost over time. They concluded that rigid shape-memory alloy staples have better final deformity correction compared with the flexible ligament tethers.

Modern vertebral body staples consist of shape-memory alloy (ie, nitinol) that allows the staple to clamp down into a C shape when it is warmed to body temperature. Literature reviewing the effect of stapling in scoliosis is limited. Betz et al40 retrospectively reviewed 21 children with adolescent idiopathic scoliosis treated with vertebral body stapling. Of the 10 children with >1-year follow-up, 60% had stable or smaller curves; 40% progressed. One patient's curve progressed to >50°, requiring subsequent fusion. In another study, Betz et al41 followed 28 children with adolescent idiopathic scoliosis treated with vertebral body stapling for 2 years. A procedure was considered successful when curves corrected >10° or corrected to within 10° of the preoperative measurement. Eighty-six percent of lumbar curves and 80% of thoracic curves <35° were successfully corrected using the stapling technique. There were no major neurovascular injuries or staple migration. Curves >35° did not do well with stapling, and the authors recommended alternative treatments.41

Crawford and Lenke42 recently presented a case report in which they used anterior thoracic screws with polypropylene tethers in an 8-yearold boy with juvenile idiopathic scoliosis and a 40° right thoracic curve. At 4-year follow-up, the curve had corrected to 6°.

Compression-based implants require continued innovation, and their use requires close follow-up to assess optimal indications and potential complications as well as a commitment to foster these novel implants through the regulatory process. Still, early work has documented “proof of concept.”

Complications

Nonfusion techniques carry with them the risk of numerous complications, with minor complication rates reported to be from 58% to 200%.22,43 Wound-healing problems, device migration, and rib fracture are common concerns. A study by Akbarnia et al9 reported a complication rate of 48% after dual growing rod implementation, with 17% of patients undergoing unplanned procedures. Meticulous surgical technique in exposing the lengthening mechanism and in closing these repeat wounds is essential. Limited subperiosteal stripping may avoid unintentional fusion, and strong foundations are key to avoid device migration and possible neurologic injury.22 Submuscular (rather than subcutaneous) instrumentation and dual rod techniques may play a role in minimizing complications. Although neurologic injuries are rare, Sankar et al44 performed a retrospective review of neuromonitoring changes in growing rod surgeries and recommended routine neuromonitoring for the insertion and exchange of growing rod constructs.

Conclusion and Future Directions

Early onset scoliosis remains a challenging problem. Growth-friendly implants such as growing rods and the VEPTR provide the surgeon with treatment options that allow control of the curve while permitting continued spine growth and pulmonary development. Although technologies to modulate growth of the spine and control scoliosis in young people appear to be viable, notable regulatory hurdles will delay widespread dissemination of such techniques. Significant research efforts are under way that seek to address many of the gaps in our understanding of how best to optimize management of patients with early onset scoliosis.

References

Evidence-based Medicine: Levels of evidence are described in the table of contents. In this article, references 6, 21, 22, 30, and 38 are level II studies. References 3, 5, 7-9, 14, 16, 23, and 27 are level III studies. The remainder are level IV or V case series, expert opinion, or animal studies.

References printed in bold type are those published within the past 5 years.

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