Early-onset scoliosis (EOS) has been defined as scoliosis of any etiology developing before the age of 10 years.1–3 Untreated EOS may cause short stature and trunk deformity with limited thoracic development, which may significantly diminish pulmonary function as lung alveoli multiplication continues until the age of 8 years.4,5 On long-term, untreated, and progressive EOS causes cardiopulmonary disease, respiratory failure and, ultimately, higher rates of mortality as compared with the general population.6–8
Healthy children without scoliosis achieve 30% of chest volume and 65% to 70% of T1-S1 sitting height by the age of 5 years.9 The spine (coronal T1-S1 height) continues to grow at a slower rate (0.9 cm/y) between the age of 5 and 10 years and then increases (1.8 cm/y) between the age of 10 years and skeletal maturity.9 Spinal fusion is typically avoided in young children to avoid long-term complications related to limited spine growth and subsequently small thoracic volume.10,11 Alternatively, growth friendly procedures are now commonly used in an effort to limit the progression of scoliosis while maximizing thoracic growth. Posterior spine-based distraction devices (growing rods) and rib-based distraction devices [vertical expandable prosthetic titanium rib (VEPTR); Depuy Synthes Spine, Raynham, MA] have been developed to correct the scoliosis and to increase spine height.12–19
Despite these benefits, a concern has been raised that serial posterior distraction surgeries may progressively lead to less spine growth. Sankar et al20 presented his theory of the law of diminishing returns of T1-S1 spine length for children treated with growing rods. The authors demonstrated that most scoliosis correction and length gain was achieved at the time of initial implantation followed by lower gain with the subsequent lengthening surgeries. In addition, the authors suggested delaying surgical treatment to avoid this phenomena commonly with serial casting.21 Casting can be challenging and may not be applicable for all children with EOS, including those with associated significant pulmonary restriction.22
Rib-based distraction with VEPTR is a well known treatment for patients with pulmonary insufficiency.14,16 When used for patients with congenital scoliosis and ribs anomalies, VEPTR was successful in controlling the scoliosis curve and in increasing thoracic volume.14,16,23 Subsequently, VEPTR has been applied to other spine conditions including EOS without ribs anomalies.15,17
In 2007, the Children s Spine Study Group (formerly the Chest Wall and Spine Deformity Study Group) initiated a prospective, multicenter study to evaluate the efficacy of VEPTR in preventing further progression of scoliosis without impeding spinal growth in the treatment of children with progressive early onset scoliosis (EOS) without rib abnormalities. The hypothesis of this study was that the VEPTR device, when used in children with EOS without ribs abnormality, is an effective method to prevent further progression of scoliosis and allows for, or at least does not prevent, spinal growth.
This is a prospective, multicenter observational cohort study to examine the outcome of rib-based distraction (VEPTR) in patients with EOS without rib abnormality at 2-year follow-up. Study approval was obtained by the Institutional Review Board at each participating center.
Patients were enrolled if they had progressive EOS that measures >45 degrees at age between 18 months to 10 years. Patients were excluded if they met one of these criteria: Presence of fused ribs or ribs abnormalities, syndromes that cause thoracic dysplasia (ie, Jeune’s syndrome), prior spinal procedures, patients participating in another clinical trial, and patients or parents who are unwilling to sign an asset/consent form.
An orthopaedic research coordinator or clinic nurse explained the study objectives and process to potential subjects. Informed consent was documented and obtained before patient enrollment into the study. The study was structured to clinically follow the patients after the initial VEPTR insertion surgery on a yearly basis throughout the course of treatment. After 5 years from the index procedure, follow-up was scheduled every 2 years until the final planned procedure or the completion of spinal growth, whichever occurs first.
The study enrollment started in January, 2007 and ended in January, 2015. Total number of the enrolled patients was 103 patients from 11 North American centers. Of these subjects, 63 had completed 2-year follow-up at the time of data analysis.
Erect spine radiographs (standing or sitting) were performed at each clinic visit (preoperative, direct postoperative, and 2-year follow-up). Calibration markers were used in each image to allow accurate height/length measurement and avoid magnification errors. The radiographs were assessed centrally by the study group to measure the major and secondary curve scoliosis magnitude and maximum spine kyphosis. Thoracic (T1-T12) and spinal (T1-S1) coronal spine height and sagittal spine length (SSL) were measured on the posteroanterior and lateral spine radiographs, respectively.24 Some patients did not have clear lateral radiographs for accurate measurement of kyphosis and SSL; therefore, we only examined their posteroanterior radiographs.
The end point of our study was the radiographic findings at the 2-year follow-up after VEPTR implantation surgery. Distraction phase change was calculated as: 2 y value−immediate postoperative value. Percentage of change at 2 years was calculated as: (2 y value−preoperative value)×100/preoperative value, similarly for distraction phase. The expected coronal spine height growth was calculated for the total 2-year follow-up period and for the distraction phase based on Dimeglio’s reference numbers.9 The percentage of coronal spine growth was calculated as: amount of spine growth/expected spine growth during similar age match period.
The primary outcome measure was the major scoliosis curve magnitude and coronal T1-S1 spine height at 2 years. Successful result was defined if one of these 2 criteria was met:
- The patient’s scoliosis magnitude at 2-year follow-up was less than or equal to the patient’s preoperative scoliosis magnitude.
- The patient’s trunk height or spinal length at 2-year follow-up was greater than or equal to the patient’s immediate postoperative trunk height or spinal length.
In contrast, failure result was defined if none of these criteria was met.
The complications were identified based on the classification system that was described by Smith et al.25
The continuous variables were examined for normality using Kolmogorov-Smirnov test. Repeated measure analysis of variance was utilized to examine changes in the study variables over time. Comparison between study groups (Table 1) was done with one-way analysis of variance when variables were normal, and with Kruskal-Wallis test when the variables were not normal. The statistical significance level was determined as P<0.05. SPPS version 20 (SPSS Inc., Chicago, IL) was used for statistical analyses.
Sixty-three patients were examined in this study and included 35 males and 28 females (Table 1). Mean age at the time of VEPTR implantation was 6.1±2.4 years. Mean follow-up was 2.2±0.4 years.
Scoliosis major curve improved from (72±18 degrees) preoperatively to (47±17 degrees) after implantation surgery (P<0.0001) followed by slight increase after 2 years (57±18 degrees, P<0.0001) but remained smaller than the preoperative magnitude. Similar changes were found for the secondary scoliosis curve and for the maximum kyphosis measurements (Table 2). Both spine coronal height and SSL continued to grow after VEPTR implantation at years of follow-up (Table 2 and Fig. 1).
Patients with syndromic and neuromuscular EOS had a higher percentage of change of SSL and decrease in kyphosis after 2 years of follow-up. Otherwise, there was no significant difference based on the etiology of scoliosis (Table 3). Figure 2 presents a case example of 2.5-year-old female with progressive EOS treated with VEPTR and shows scoliosis correction at 2-year follow-up.
The severity of preimplantation scoliosis was not a factor that influenced percentage scoliosis correction of the major curve; however, there was a larger percentage correction of the secondary scoliosis curve in subjects with severe (>90 degrees) preoperative scoliosis. Patients with moderate (51 to 90 degrees) preoperative scoliosis had a lower percentage of change in coronal spine height compared with mild and severe preoperative curves. Patients with severe (>90 degrees) preoperative scoliosis had greater percentage of change in T1-S1 SSL and a trend toward greater percentage change in maximum kyphosis (Table 4).
Success of VEPTR treatment of major scoliosis curve was found in 54 patients (86%) (Table 5). Success based on improvement of coronal T1-T12 and T1-S1 spine height was found in 42 patients (86%) and 46 patients (93%), respectively. It was noted that SSL increased during the distraction phase in 82% and 84% of the patients for T1-T12 and T1-S1 SSL. Similarly, the instrumented segment SSL also increased in 82% of patients during the distraction phase (Table 5). Composite success of controlling the major scoliosis curve and improving the coronal spine height was found in 42 patients (79%).
Spine height growth during 2-year follow-up represented 144% of expected age-matched coronal T1-T12 growth and 193% of expected age-matched coronal T1-S1 growth. In an effort to exclude the height gained simply by the initial curve correction during implantation surgery, spine growth was also evaluated during distraction phase: 40% of expected age-matched coronal T1-T12 growth and 31% of expected age-matched coronal T1-S1 growth was achieved at 2-year follow-up.
Thirty-one patients had at least 1 complication (49%). Total number of complications was 58 (Table 6). On the basis of Smith classification: thirty-nine complications were device related (24 were grade 1 and 15 were grade 2). Nineteen were disease related (12 were grade 1 and 7 were grade 2).
The objective of this study was to evaluate the efficacy of VEPTR in preventing further progression of scoliosis without impeding spinal growth in children with progressive EOS without rib abnormalities. This prospective multicenter study has demonstrated that, at 2-year follow-up, VEPTR was effective in treating EOS without rib abnormalities. VEPTR allowed improvements of scoliosis curve with an ability to provide >100% of expected age-matched spine growth. The findings of our study were consistent with previous studies where VEPTR was found successful in preventing scoliosis progression and allowed spine growth.12–18,26 In addition, it was determined that the instrumented spine segment continued to grow during the distraction phase.
Thoracoplasty with VEPTR implantation allows expansion of the chest and gradually corrects the spinal curve with every VEPTR lengthening.15,17,18 This postulation was not yet fully supported in the literature. There is still a concern that implementing spine distraction at an early age could render spine growth and cause spine autofusion over time.20 Sankar et al20 examined patients with EOS who were treated with posterior spinal based distraction (growing rods) and observed decreases in spine height gain after each growing rod lengthening which was termed “the law of diminishing returns.” This law was also evaluated for rib-based distraction surgeries. The Children's Spine Study Group examined the outcome of rib-based distraction treatment in patients with a heterogeneous mix of scoliosis etiologies including congenital scoliosis associated with ribs fusion. In this study, 35 patients were treated with rib-based distraction which shown to be effective in controlling the scoliosis curve and in allowing the spine to continue to grow.15 The patients had an increase in total coronal spine height from 20 cm preimplantation to 28 cm by the 15th lengthening. They maintained >75% of expected age-matched spine growth until age 10 years and lengthening procedures did not appear to follow a law of diminishing returns. Similar findings were shown by Flynn et al17 who examined VEPTR implantation in patients with nonsyndromic EOS.
Our study presented comparative findings to other studies on growth friendly procedures and demonstrated effective improvement of scoliosis curvature at instrumentation with subsequent maintenance albeit with minor increase of curvature.15,20,23 Studies on spine distraction showed increased spine kyphosis following repeated lengthening.15,17,20,26,27 Because VEPTR causes increased spinal kyphosis with distraction, coronal spine height measurements can be an underestimate of what a “true” spine height would be.15,24 To take into account changes in the sagittal plane that may occur with repetitive posterior distraction surgeries, SSL was developed and validated.15,24 In addition to traditional coronal plane measurements of spine height (which can be normalized to expected age-matched growth), we also evaluated the SSL to ensure that the kyphogenic effects of repetitive posterior distraction surgeries were taken into account. In our study, we found that the coronal spine height and the SSL each increased during the first 2 years after implantation. This increase has 3 likely components: the effect of scoliosis correction during the initial insertion procedure, the effect of mechanical distraction during each lengthening surgery, and the actual spine growth by every vertebral segment. As expected, the effect of curve correction was maximum at the time of implantation surgery.17 We also found that the instrumented coronal spine height continued to increase by 40% of expected age-matched coronal T1-T12 growth and 31% of expected age-matched coronal T1-S1 growth during the distraction phase. This was also seen evident with SSL measurement of the instrumented spine segment increasing in 82% of subjects.
Our study reports a 49% complication rate that is comparable with what reported in the literature (41% to 55%).16,28 On the basis of Smith classification only 17% of the complications needed unplanned surgical intervention.
EOS is a heterogenous condition with different etiologies that created a heterogenous patient sample. We were limited by the number of enrolled patients in the study to examine outcome of treatment in 4 curve types based on EOS classification.3 The small sample size in each group limited the power of our study with possible type II error. The fact that the study was based in different institutions could be a confounder since different surgical indications and implantation techniques might have been implemented. In addition, although spine radiographs were taken using a standard fashion, we acknowledge that some patients’ posture and positioning might have been affected by their health status and ability to stand up for upright radiograph with possible measurement error. This error was not significant and was overcome by using appropriate statistical analysis methods. In addition, we acknowledge that comparing different instrumentations such as VEPTR and growing rods is valuable, however, this cannot be applied to our study. This study reports the short-term results of prospective multicenter study that only enrolled patients with EOS without ribs abnormality who were managed with VEPTR. Growing rods were not part of the study and therefore we were unable to do a comparative assessment. We think a consideration of such comparison study would be significant to better understand EOS treatment.
Despite these limitations, our study strength was driven by its prospective design. The primary outcome measures and hypothesis were developed a priori before other studies that have been published since the initiation of this study. A multicenter setting allowed increased sample size of this rare orthopaedic condition. We selectively included patients who had EOS without ribs anomalies or rib fusion to reduce heterogeneity and to evaluate the latest Food and Drug Administration indication for the VEPTR device.
At 2-year follow-up, this large prospective, multicenter study demonstrated the ability of VEPTR to effectively treat EOS without rib abnormalities. Goals of preventing further scoliosis progression and of maintaining spine growth were achieved. This study proved that spine continues to grow after VEPTR instrumentation during the distraction phase. This amount of growth represents about 40% for T1-T12 and 31% for T1-S1 spine of the expected age-matched growth based on Dimeglio reference numbers. We find this growth important as it proves continuous spine growth with VEPTR treatment.
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