7 Novel Nonfusion Growth-Modulating Techniques for Pediatric Scoliosis
Introduction
It is well understood that curve correction in the growing child′s spine does not always result in a healthy child due to the potentially life-threatening long-term side effects of early spinal fusion. Definitive fusion in a growing spine retards or halts longitudinal spinal growth, spinal canal formation, thoracic cage growth, and lung development. This results in a disproportionately short trunk, possible crankshafting and adding on, and respiratory insufficiency.
As the drawbacks of early fusion were better understood, the concept of “delaying tactics” was suggested. 1 These nonoperative and operative tactics aim to delay fusion for as long as possible, if not to totally avoid it. Nonoperative delaying tactics include traction, casting, and bracing. Operative delaying tactics intend to control the deformity while allowing growth of the spine, thoracic cage, and lungs. 2
Growth-modulating procedures such as vertebral body stapling and tethering may provide substantial advantages over both nonoperative and operative delaying tactics, and may lead to definitive spinal fusion in a selected group of patients. The purpose of growth-modulating methods is to harness the patient′s inherent spinal growth and redirect it to achieve correction, rather than progression, of the curve. 3 This is accomplished by applying compressive forces on convexity via an anterior approach.
Overview of Nonfusion Techniques
Nonfusion surgical techniques are employed to achieve deformity correction; to allow spinal, thoracic cage, and thus lung growth; to maintain correction during the growth period; and to postpone or avoid fusion. The most commonly used nonfusion techniques can be grouped in four categories ( Table 7.1 ). Growth preservation/stimulation, growth guidance, and growth modulation are the three main surgical philosophies. Combinations of these techniques with or without limited fusion are referred to as the fourth category of hybrid constructs. Growth modulation is discussed in detail later in this chapter. Detailed information on other growth-sparing techniques can be found in Chapter 5.
Growth preservation and stimulation techniques are distraction-based constructs in which a mobile spinal segment exists with anchor foundations at either end. They are named based on the location and type of the foundations. Regular lengthenings are applied to control or correct the curves while preserving and possibly reinforcing the spinal growth due to the effect of distraction on immature vertebral growth. 4 , 5 But observations of spinal fibrosis, ankylosis, and autofusion led to criticism of such techniques. 6 , 7 Additionally, these constructs were associated with numerous planned and unplanned reoperations with a high rate of complications, including anchor dislodgment or rod breakages, wound problems, and alignment issues. 8 Although the ideal has probably not yet been reached, more recently available magnetically controlled growing rods can be lengthened noninvasively, reducing the number of repetitive surgeries. 8
Growth guidance techniques include apical control to achieve a better correction and lessen the transitional stresses on the unfused spine while abandoning the effect of the use of distractive forces. These self-sliding assemblies preclude the need for many additional procedures and provide adequate maintenance of curve correction in most cases, although the spinal growth obtained may be less than expected. 9
Hybrid constructs may include convex growth arrest plus concave distraction, 10 limited fusion plus growing rods, and distraction-aided growth guidance. Maruyama et al 11 defined a fusionless procedure of noninstrumented multiple vertebral wedge osteotomies via open thoracotomy as a definitive surgical treatment of immature and mature adolescent idiopathic scoliosis (AIS).
Growth Modulation for Pediatric Scoliosis
Treatment options for skeletally immature idiopathic scoliosis patients with moderate curves have long been limited to observation and bracing. 12 , 13 Observation resulted in spinal fusion in 75% of pubertal onset curves between 21 and 30 degrees and 100% of curves > 30 degrees at the onset of puberty. 14 Observation entails taking periodic radiographs, and the patient and family can experience anxiety associated with the possibility of progression.
Bracing has therefore remained the standard of care, although clinical results widely varied. The recent Bracing in Adolescent Idiopathic Scoliosis Trial (BrAIST) found that appropriately prepared and worn braces reduced the need for surgical treatment by 50%. 13 Nevertheless, brace wear requires the child′s commitment for 16 to 23 hours per day. The brace is cumbersome and uncomfortable, especially in warm climates and during the summer. Brace treatment typically requires 3 to 5 years, and possibly even longer depending on when the child starts wearing one. As bracing requires significant compliance and can have social implications, the potential success of this treatment modality can be compromised. Furthermore, some patients experience psychosocial stress regarding their body image; they feel that their body asymmetry is worse than that of untreated scoliosis patients, despite similar curve sizes. 15 , 16
In a logical sense, patients bear the cumbersome bracing treatment not to avoid surgery but to avoid spinal fusion, which, to date, remains the most viable surgical option in scoliosis treatment. Yet fusion entails decreased spinal mobility, decreased range of motion, inhibition of growth over the length of the construct, and the possible development of adjacent segment degeneration. 17 – 19
Thus, growth- and motion-sparing strategies that modulate the growth of the spine, stabilize the curve, and avoid spinal fusion are alternatives to bracing for the treatment of progressive scoliosis. These growth-modulating techniques address the remaining spinal growth of the child and are generally referred to as tension-based or convexity compression methods. The logic behind applying compression to the convexity of the curve is based on the Hueter-Volkmann law that states that a growth plate under pressure will grow more slowly than one that is subjected to less pressure. 20
Vertebral Body Stapling
Vertebral body stapling is an alternative to bracing for the treatment of progressive scoliosis in late juvenile and immature AIS.
Interestingly, vertebral stapling originated in the 1950s, when wire staples were placed across the disk spaces. The Hueter-Volkmann principle was first tested in canines 21 and then applied in three humans. 22 When this attempt was unsuccessful due to implant migration, the procedure was abandoned until recently.
Implant design with shape-memory metals and use of video-assisted thoracoscopy have breathed new life into this procedure. 23 Nitinol (an acronym for the former Nickel Titanium Naval Ordnance Laboratory, White Oak, MD, where it was developed) is a biocompatible shape-memory metal alloy that is implanted in a cooled state. The prongs of the staple are perpendicular. Once the metal warms to body temperature, the prongs clamp down on the end plate, providing a gentle compressive force and diminishing the risk of pullout. 24
Surgical Technique
For thoracic curves, the child is placed in the lateral decubitus position, with the curve convexity facing up. 25 To enable slight correction of the curve, an axillary roll is placed underneath the concave side. Video-assisted thoracoscopy is used with single lung ventilation and carbon dioxide insufflation. Vertebral bodies are identified using biplanar fluoroscopy. Staples are first placed in ice.
The instrumentation is performed from end to end vertebrae. Care is taken to protect the segmental vessels because they are located in the middle of the body and not in the implantation site. A trial is used at every level to gauge the size. To help with the correction, the trial device can be used to push on the apex. Then the trial is removed and the staple is quickly inserted. Optimal staple placement requires that the prongs be close to the vertebral end plate. 25 The staple is placed anterior to the rib head in the sagittal plane. A more anterior position is desired in hypokyphotic curves. After the optimal position of the staple is fluoroscopically confirmed, the staple is impacted in the vertebral body. These steps are repeated at every level. At the end of the procedure, a chest tube drain is placed. 25
For lumbar curves, a direct lateral, retroperitoneal approach with a minimal open incision 26 is preferred. 25 The psoas muscle is retracted posteriorly or is separated longitudinally over the posterior half of the disk under electromyographic control. Staples are placed at three or four levels in the posterior half of the vertebral body. 25
It is important to maximize the intraoperative correction, because results are more favorable when curves are reduced to < 20 degrees in the first standing radiographs. 25
Results
Vertebral body stapling works by slowing the growth of the convexity of the curve using the same principle as hemiepiphysiodesis. Shape memory staples compress and bridge the growth plates to reversibly reduce or block growth. In theory, implants avoid the need for definitive asymmetric spinal fusion. Yet there are concerns regarding stiffening of the instrumented segments 27 that may lead to disk degeneration or spontaneous fusion. Betz et al 24 demonstrated the feasibility, safety, and utility of this technique in immature AIS.
To better interpret the results, thoracic and lumbar curves should be analyzed separately because they respond differently to stapling. Betz et al 28 reported results for stapling of 52 curves in 39 patients of ages 8 years and older, in whom progression was ♀ 10 degrees in 87% of the patients at a minimum 1-year follow-up. Longer follow-up revealed similar results of ♀ 10 degrees progression of ~ 78% in all lumbar curves and thoracic curves < 35 degrees. 25
Later, the same group compared the results of stapling versus bracing in moderate scoliotic patients with a high-risk of progression. 29 The success rate for 25- to 34-degree thoracic curves was 81%, versus 61% for stapling and bracing. For larger thoracic curves measuring 35 to 44 degrees the treatment success rate was 18% versus 50% for stapling and bracing. For lumbar curves of 25 to 34 degrees, the success rates for stapling and for bracing were similar, 80% and 81%; for larger lumbar curves, however, these success rates were 60% and 0%. Nonetheless, it is difficult to draw any conclusions for > 35- degree lumbar curves, because only five patients underwent stapling, and only two were braced. 29
Poor results were consistently reported in thoracic curves > 35 degrees. 25 , 28 , 29 In these curves, the general mode of failure was that the instrumented curve remained stable, but the curvature increased at the two ends of the construct, 30 subsequently necessitating fusion. In contrast, in a series of 12 children younger than 10 years of age with thoracic and lumbar scoliosis of 30 to 39 degrees, vertebral body stapling was found to be effective, as the chil dren either had no change in their curve or had curve improvement. 31
Complications associated with stapling, although infrequent, include dislodged or broken staples, curve overcorrection, pneumothorax, congenital diaphragmatic hernia rupture, contralateral pleural effusion, and superior mesenteric artery syndrome. 25 , 29 , 32 , 33
Related posts:
1 Early-Onset Scoliosis: Classification and Natural History
2 Adolescent Idiopathic Scoliosis: Classification and Natural History
8 Long-Term Outcomes of Operative Management in Adolescent Idiopathic Scoliosis
3 Preoperative Evaluation and Imaging Techniques in Adolescent Idiopathic Scoliosis
16 Safety and Complications in Pediatric Surgery
15 Spine Surgery in the Developing World
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