Progressive scoliosis in young children may be caused by a multitude of very different conditions, while the cause of the most common type of scoliosis – idiopathic scoliosis – is yet to be discovered. Not all scoliotic curves progress, however; currently, there is no known definitive medical means to stop worsening of a scoliotic curve if the curve is of progressive character. Because of the relentless progression and possible drastic consequences of spinal deformity, spinal fusion surgery may be required to stop the progression and provide correction.
In a relatively mature spine with no or minimal amount of remaining growth, spine fusion results in loss of motion and a likely detrimental effect on the neighboring mobile segments. However, in an immature, young spine with a considerable amount of growth, the trunk growth is permanently stunted, depending on the amount of remaining growth. The most drastic end result of an early fusion affects the thoracic spine, where a certain amount of thoracic height is required for the normal functioning of the pulmonary system [1,2]. To that end, surgeons have been looking into ways to maintain the growth of the spinal column, while correcting the abnormal spinal curvatures.
In modern times, there is no evidence showing the benefit of physical therapy or manipulation to control or correct scoliosis. Surgery may be avoided or delayed using casting techniques in certain types of scoliosis [3,4] and there is good evidence showing that in children with mild idiopathic curves (<60°), if cast treatment is started early (<20 months of age), full correction may be expected . However, rapidly progressive curves require surgical stabilization for control of the progression.
Currently, a number of different spinal instrumentation systems are being utilized in order to correct and control spinal deformities and enhance pulmonary development in young children with scoliosis and kyphosis. A classification first proposed by Skaggs et al. provides a practical description based on the mechanism of action of each system. According to this classification, growth friendly methods may be subdivided into three categories: distraction-based [growing rods, vertical expandable prosthetic titanium rib (VEPTR)]; guided-growth (Luque-trolley, Shilla); and compression-based (staples/tether) techniques.
This review presents the recent developments in the currently available growth friendly instrumentation methods for early-onset scoliosis (EOS).
Harrington  reported on using his distraction system without fusion, to correct and control curves in young children. However, it was not until late 1990s that good results started to appear in the orthopedic literature [8,9]. Since then, there have been numerous reports from all around the globe using different instrumentation methods that utilize the growing rods principles.
Briefly, the growing rods system is composed of vertebral anchors (hooks or pedicle screws) and rods that are connected to these anchors. Typically, a third unit, which is a telescopic connector, is also used. This telescopic unit connects the proximal and distal rods and the lengthening is achieved by distracting the rods through this connector (Fig. 1). Growing rod treatment in children with idiopathic EOS provides correction of the deformity with a low frequency of major complications . However, overall complication rate is high and implant-related complications such as rod breakages and screw/hook pull-outs occur commonly . As most of the anchor (screws/hooks) pull-outs are at the proximal end of the construct, supplemental rib fixation may be utilized to avert this complication. Proximally, rib fixation may also be utilized ‘solo’, as in VEPTR instrumentation. Rib anchors provide a less rigid fixation of the spine and may, therefore, help avoid implant breakages and pull-outs. These complications frequently require implant revisions, mostly during planned lengthening surgeries. Because of the good results achieved in children with idiopathic scoliosis, most centers started utilizing growing rods in other types of EOS such as congenital, syndromic, neuromuscular, and skeletal dysplasia. It must be remembered that, because of the nature of the technique, children with other medical issues may be more prone to complications. This has been confirmed by a recent study on patients with cerebral palsy, in which a very high rate of complications has been reported .
There has been increasing research on the magnitude of spinal growth that is achieved during the growing rod treatment. Rates of spinal growth during growing rods treatment appear to be around the normal or even higher than the normal growth rate [9,10]. Olgun et al.[13▪] recently reported that the growth within the instrumented segment is higher than the growth outside the instrumented part of the spine. This finding indicates that the distraction through growing rods may be stimulating the growth of the spinal column at individual end plates (following the Hueter–Volkmann principle) and may explain the higher than normal spinal growth rates. Our experience with growing rods is similar to what has been reported by others, that good results can be expected, especially in children with early-onset idiopathic scoliosis, and final fusion surgery may be reliably delayed. However, frequent and repetitive surgery for lengthening is the most important drawback of this technique. Spontaneous fusion/ankylosis of the noninstrumented segments and complicated surgery at the time of definitive fusion are also potential disadvantages.
VERTICAL EXPANDABLE PROSTHETIC TITANIUM RIB/EXPANSION THORACOPLASTY
Expansion thoracoplasty is a technique that utilizes a VEPTR or a similar construct with or without a thoracotomy at the initial implantation surgery (Fig. 2) . Similarly to growing rods, expansions are done 6 months apart. This technique was pioneered by Campbell et al. in order to increase the pulmonary volumes, enhance the pulmonary function, and control the spinal deformity of children with thoracic insufficiency syndrome (TIS) and spinal deformity. Subsequent studies demonstrated the positive effects of VEPTR expansion thoracoplasty on the pulmonary function and volumes [16–18]. Interestingly, one study reported that, along with the improvement in pulmonary function, these children gained a significant amount of weight after the initiation of VEPTR treatment . This is an important finding, as failure to thrive can be a significant health problem in the majority of children with TIS and EOS. Additionally, despite the frequent presence of congenital vertebral and rib anomalies in children with TIS and EOS, multiple studies showed growth rates of the thoracic spine similar to normal growth [17,20,21]. Although initially the VEPTR device was developed to be used in children with TIS, the indications have been expanded over time. Various authors reported the use of the VEPTR device in treatment of EOS, older children with complex spine deformities, congenital scoliosis, myelomeningocele kyphosis, and neuromuscular scoliosis [21–25].
VEPTR treatment requires multiple recurrent surgical procedures to achieve expansion. Due to the nature of the technique and the recurrent surgeries, multiple implant-related and wound complications are associated with VEPTR treatment. Major complications are rare and most other complications can be addressed during expansion surgeries. Despite the number of complications and recurring surgeries, a study looking at the health-related quality of life (HRQL) reported that there were no significant differences in HRQL scores in children under VEPTR treatment before and after treatment .
Recently, some concerns have been raised associated with the use of VEPTR-type instrumentations that overlie the chest wall [27,28▪,29▪]. Specifically, the use of VEPTR has been associated with spontaneous rib and vertebral fusions that may worsen the spinal balance in addition to increasing the stiffness of the deformity and the chest wall [28▪,29▪]. Current evidence suggests that the risk of these ossifications may increase after 4 years of treatment with VEPTR. For children who have been treated for EOS associated with chest deformity, a final arthrodesis of the spine is often necessary once satisfactory growth has been achieved. Lattig et al. reported that the final arthrodesis of the spine may become very challenging and risky for the patients who had been treated with VEPTR secondary to development of high thoracic hyperkyphosis, autofusion of the ribs and vertebral bodies, and curve progression. VEPTR is still the most advanced surgical technique to address the underdeveloped chest wall in TIS and we utilize it for this specific indication. Currently, there are no better alternative treatment modalities for children with constricted, immobile chests and spinal curvatures that are caused by the tethering from the thoracic cage deformity. However, for the thoracic deformities secondary to the spinal curvature (i.e., primary spinal deformity), spinal implants should be preferred.
The first self-growing rod system is most likely the one that was introduced by Luque and Cardoso . The technique required extensive dissection since sublaminar wires were utilized to attach the spine to rods. The idea is that, as no fusion is attempted, the rod-wire system acts as an internal brace and the spine could grow over this system. However, on longer follow-up, spontaneous fusions and difficulty of revision surgery were reported . This method is of historical significance for growing spine surgery, as with the amount of dissection required the risk of spontaneous fusions is high and the possible growth is minimal. Although the Luque trolley method fell out of favor, there has been an increased interest in the self-lengthening concept [32,33]. However, the safety and efficacy of these systems need to be confirmed on larger patient series with longer follow-up. The most commonly known type is the ‘Shilla’ technique, which requires special vertebral anchors that allow gliding of the rod (Fig. 3) [34,35]. The 2-year follow-up clinical outcomes of the Shilla technique have recently become available . The common idea is to control the apex of the deformity by connecting the apical vertebrae to the most proximal and distal parts of the deformity. These systems theoretically allow self-lengthening of the construct through the gliding motion of the rods inside the proximal and distal anchors as the child grows. Therefore, these systems typically require multiple levels of anchor placement and limited fusions.
MAGNETICALLY CONTROLLED SYSTEMS
One of the most exciting developments in growing spine surgery is the introduction of magnetically controlled growing rod (MCGR) systems. In order to avert the need for recurrent lengthening surgeries, recent efforts have been directed at developing a remotely controlled growing rod system, and different systems have been reported [36,37▪▪]. The technique is similar to growing rods as pedicle screws and rods are utilized (Fig. 4). However, instead of the telescopic connector, a telescopic actuator that holds a small internal magnet is used. The interaction of this magnet with an external remote controller causes the rod to be lengthened or shortened [37▪▪]. In an animal study, MCGR was proved to provide distraction through noninvasive remote distraction without complications . A recent clinical study confirmed that distraction can be safely and effectively achieved in children with EOS in the short-term follow-up . Another recent clinical study involved five international centers and reported the good results of MCGR in 14 patients with EOS secondary to mixed etiologies [37▪▪]. This technology can potentially be applied to expansion thoracoplasty techniques.
This method is different from the aforementioned methods in that vertebral growth is modulated but not guided. Simply put, tethering and stapling methods aim to achieve a hemiepiphysiodesis effect in order to slow down the growth of the convex part of the deformity apex and allow the growth of the concave side. This is a relatively old concept  and there are many reports of vertebral hemiepiphysiodesis in the literature with mixed results. Most recent clinical reports show that vertebral stapling may be effective for idiopathic curves with moderate severity [41,42] and may not be effective in other complex scoliosis types such as congenital, syndromic, myelomeningocele, and neuromuscular . Although recent animal studies using anterolateral spinal tethering have been encouraging [44,45], very limited clinical experience is present (Fig. 5) . The most attractive feature of this technique is the possibility of a definitive correction without final fusion surgery. However, unless the indications could be extended to more severe curve patterns, we find it unlikely that this technique would be adopted by most.
Growth friendly (but not fusionless) scoliosis surgery is currently temporizing at its best, and the fusionless definitive treatment goal is still out of our reach. It appears that a combination of growth modulation and guidance with the least invasive intervention would be the optimal treatment method. The conquest of fusionless scoliosis treatment will most likely involve extensive laboratory studies in the hands of innovative minds.
Conflicts of interest
M.Y. is a paid consultant for Ellips Technologies and Depuy Synthes Spine. O.D. and G.D. do not have any conflict of interests to report.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
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A radiographic study demonstrating the effects of distraction on vertebral growth. This study supports the Hueter–Volkmann law in that distractive forces exerted upon growing physes stimulate growth. This study is important in that the results indicated that the growing rods treatment may not only preserve but also stimulate the growth of individual vertebral bodies within the instrumented segment.
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This study showed that spontaneous fusions between unexposed and uninstrumented vertebrae may occur after expansion thoracoplasty.
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This clinical report demonstrated the occurrence of ossifications over the thoracic wall and the spine after VEPTR treatment in children. This is important as a stiffer chest and spinal deformity may ensue.
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Multicentered study reporting very encouraging results with the use of a MCGR construct in EOS. Though encouraging, this study is one of the earliest reports and longer follow-up will be needed in order to define the use of this method in EOS.
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