Patient-Reported Outcomes Are Equivalent in Patients Who Receive Vertebral Body Tethering ... .




Scoliosis is the most common spinal disorder in pediatric patients, characterized by curvature of the spine and typically rotation of the vertebrae. The overall prevalence found in the literature ranges from 0.47% to 5.2%, with a female to male ratio ranging from 1.5:1 to 3:1 and increasing with age and curve severity.1 Juvenile idiopathic scoliosis and adolescent idiopathic scoliosis (AIS) present in otherwise healthy children with age of onset between 3 and 10 years and 11 and 18 years, respectively.1,2 Both diagnoses pose a possibility to progress the need for surgical intervention.

Posterior spinal fusion is the standard of care for curves at or near 50° in AIS and juvenile idiopathic scoliosis and has been shown to achieve reliable deformity correction with a low rate of complication.3 Anterior vertebral body tethering (AVBT), or spinal growth tethering, is an emerging technology that has recently received Food and Drug Administration (FDA) approval through a humanitarian device exemption designation to treat idiopathic scoliosis patients with remaining growth. Because of the novelty of the technique, little has been published prospectively on the subset of the patient population seeking this alternative treatment. It is conceivable that those seeking a new treatment differ from those treated with the gold standard and thus the results of any comparison of the treatments could be confounded. For evaluating outcomes, it is important to recognize whether any distinction lies in the clinical, radiological, or patient-perceived quality-of-life characteristics between those who undergo spinal fusion vs tethering. The purpose of this study was to examine these patient populations to determine whether there are inherent differences in patients and families who seek vertebral tether.

Materials and Methods

Following institutional review board approval, the authors reviewed 62 patients from a prospective multicenter database of idiopathic scoliosis patients who underwent posterior spinal fusion (PSF) treatment and 20 patients from an FDA-approved investigational device exemption clinical trial who received the AVBT intervention. Study data for the investigational device exemption trial were prospectively collected from 2017 to 2020 and managed using REDCap electronic data capture tools.4,5 Patients in the multicenter database were from 15 different institutions and treated from 2000 to 2018. Surgical patients were included if, preoperatively, they had a curve type classified as either Lenke type 1 or type 2 with a thoracic curve between 35° and 60°, a lumbar curve less than 35°, and a skeletal maturity score of either Risser sign 0 or Sanders bone age of 4 or less. Selection criteria were based off curve severity and skeletal maturity parameters defined in the tether investigational device exemption trial eligibility criteria.

The authors examined demographics, clinical variables, radiographic measures, and health-related quality of life (HRQOL) scores from patients' preoperative visit for comparison between the two cohorts. These included sex, age, race, height, weight, pulmonary function, rib hump, flexion, anteroposterior/lateral/bending curve degrees, and Scoliosis Research Society Questionnaire Version 22 (SRS-22) scores.

The Kolmogorov–Smirnov test was used to assess the normality of distributions. The Mann–Whitney–Wilcoxon test was used to compare nonparametric variables. A two-tailed independent t test was used for parametric variables after determining equality of variances using Levene's test. Fisher's exact test was used to compare categorical variables. Statistical significance was set at P<.05. The data were analyzed using Stata, version 15.1, software (StataCorp LLC).


A total of 82 skeletally immature patients (70 female and 12 male) were recommended for surgical intervention for their scoliosis. Patients had a mean age of 11.7 years (SD, 1.2 years; range, 8–16 years) at the time of surgery, and a mean thoracic curve of 50.4° (95% CI, 49.1–51.7) and lumbar curve of 27.0° (95% CI, 25.6–28.4) at their preoperative visit. The majority of patients (n=78; 95%) had a right thoracic curve.

The patients were divided into groups depending on the surgical treatment received: PSF (n=62) or AVBT (n=20). There was a similar distribution of sex (P=.47) and race (P=.50) as well as similarity in age (P=.83) between the cohorts. Of 31 fusion patients who reported their home location, only approximately 10% lived out of town, with the rest being local to the institution they visited for surgical treatment. Conversely, approximately 40% of the AVBT cohort were not local when seeking treatment. There was also no difference in mean patient height (153.2 cm vs 155.5 cm, P=.43) or weight (47.2 kg vs 46.4 kg, P=.82). Adam's forward-bending test was used to measure rib hump degrees, and the forward/lateral flexion test was used to assess bending flexibility. No statistically significant differences were seen between the groups (Table 1). The forced expiratory volume in 1 second (FEV) and forced vital capacity (FVC) data were available for all patients in the tether cohort (n=20). The mean FEV was 2.15 L (range, 1.13–3.07 L), with predicted FEV of 78% (range, 47%–150%). The mean FVC was 2.63 L (range, 1.24–3.76 L), with predicted FVC of 82% (range, 56%–141%). Data were available for 28 PSF patients. The mean FEV was 2.01 L (range, 1.24–2.62 L), with predicted FEV of 78% (range, 47%–111%). The mean FVC was 2.37 L (range, 1.50–2.88 L), with predicted FVC of 83% (range, 56%–109%).

Demographics and Clinical Factors

Table 1:

Demographics and Clinical Factors

Among the tether patients, 90% were classified with a Lenke type 1 curve, while 10% had a Lenke type 2 curve. Similarly, 71% and 29% of fusion patients were type 1 and type 2, respectively (P=.21). Lumbar and sagittal thoracic modifiers were not different (P=.44), with most patients classified as type 1AN. The thoracic apex ranged from vertebral levels T6 to T11 for fusion patients and from T8 to T11 for tether patients. The apex was most commonly at T9 (26%) and the disk space between T8 and T9 (30%) for fusion and tether patients, respectively (Figure 1). Patients identified for surgery presented with a mean thoracic curve of 50.2° for fusion and 51.1° for tethering (P=.56); lumbar curves were a mean of 27.0° for both groups (P=.78). Thoracic kyphosis and lumbar lordosis measures were similar (P=.95 and P=.60). Tether patients tended to bend and correct their thoracic curve better than fusion patients (21.3° with 59% correction vs 29.6° with 43% correction; P=.01 and P=.005). This, however, did not hold for lumbar curves (P=.12 and P=.24; Table 2).

Location of thoracic curve apex.

Figure 1:

Location of thoracic curve apex.

Radiographic Measures

Table 2:

Radiographic Measures

Patient-reported outcomes from the SRS-22 questionnaire were compared by total score and scores across the 5 domains—pain, self-image, function, mental health, and satisfaction with management. The two groups scored similarly overall (P=.70) and within each domain (Figure 2). Examining the proportion of patients who scored below 4.0 between those who eventually underwent fusion or tether also revealed a statistically insignificant difference. For example, 30% of tether patients scored less than 4.0 in mental health compared with 43% of fusion patients (P=.42).

Scoliosis Research Society Questionnaire Version 22 scores across each domain. Abbreviations: AVBT, anterior vertebral body tethering; PSF, posterior spinal fusion.

Figure 2:

Scoliosis Research Society Questionnaire Version 22 scores across each domain. Abbreviations: AVBT, anterior vertebral body tethering; PSF, posterior spinal fusion.


Vertebral body tethering has become more familiar to both patient families and physicians alike; analogously, the technique has also been increasing in use and popularity. At the same time, research efforts are needed to keep up with the pace of clinical innovation. Risks and benefits of the technique need to be compared with outcomes from interventions such as PSF, which has the advantage of a large body of historical data describing it.6,7 This study is an initial step toward this goal, as the authors prospectively examined the epidemiology of idiopathic scoliosis patients who received AVBT compared with PSF to determine whether there are differences in these groups recommended for surgical intervention.

It is important to collect and report on a comprehensive dataset of relevant baseline variables in both treatment and control groups to understand the comparability of the cohorts, as such differences may confound comparisons of treatment outcomes, particularly when discussing non-randomized trials. These quasi-experimental designs are particularly common in surgical intervention studies.8 Baseline data can be useful in subgroup analyses and covariate-adjusted analyses.9 For example, several studies that compared spinal implants and interventions had noted variations in preoperative characteristics such as age, sex distribution, Cobb angle, and/or HRQOL scores between groups that would have affected the interpretation of results and therefore required strategies such as matching or controlling for confounders.10–12

In the current study, the patients who sought and received tether treatment generally resembled those who underwent PSF and had demographic characteristics similar to those of the AIS population.1,13 The female to male ratio for tether patients was 4:1 in the current study, reflecting the higher prevalence of severe curves in females.1 Almost half of the tether patients did not come from the authors' immediate catchment area, as the technique has limited availability compared with spinal fusion. In this study, the mean age at surgery was approximately 11.8 years, which is before the maximum spinal growth velocity supported in the literature of between the ages of 11.5 and 12.5 years for females and approximately 15 years for males, particularly important to ensure that growth modulation is achieved.14 Relatedly, all tether patients had a Sanders bone age of 4 or less, and the mean Sanders bone age of 3.3 was similar to the 3.2 of the cohort of 32 patients studied by Samdani et al.15 The mean preoperative major curve that the tether patients presented with, 50.2°, is considered to be severe. This is comparable to the fusion patients in the current study as well as the tether cohorts reported by Newton et al,16 Crawford and Lenke,17 Samdani et al,18 Samdani et al,15 and Boudissa et al,19 who had mean major curves ranging from 40° to 52°. Thoracic curves were also more flexible in tether patients than in fusion patients, as measured on bending radiographs. Likewise, other studies have published average flexibility rates ranging from 48% to 60%.15,16,19 Ideally, patients who undergo tethering will have high flexibility before treatment and be able to maintain their degree of motion following intervention.20

To the best of the authors' knowledge, no studies have prospectively described tether patients' self-evaluation of their health status. In this study, tether patients and fusion patients were alike in their self-reported quality of life when assessing SRS-22 scores, across all domains. Unlike originally hypothesized, patients who seek tether treatment may not necessarily be different from their peers in how they perceive aspects of daily living such as pain, level of functioning, self-image, mental health, or satisfaction with disease management. A review of other studies of AIS patients who underwent fusion surgery showed variable SRS results as well as methods of reporting the data. Total scores ranged from 3.6 to 3.9.21–23 Therewere no clear trends when comparing between the domains, but typically self-image tended to score relatively lower, ranging from 3.0 to 3.6, as in the current study.21–23

The limitations of this study included a methodology that compared a multicenter database of fusion patients with a single-center perspective of tether patients. To address this concern, an analogous multicenter registry of tether patients is currently being planned. At the same time, it will be essential that as many data points for predefined variables be collected as possible. For example, the fusion cohort in the current analysis had incomplete pulmonary function test results, limiting the authors' ability to analyze patients' respiratory function. Finally, this study did not report on outcomes between the treatment options due to lack of sufficient follow-up. Such efforts are ongoing and in the future will help contribute to the preliminary body of work reported on growth modulation in patients.


The authors described patient cohorts treated with either PSF or AVBT. On comparisons of the two groups, they found that, other than thoracic flexibility, there were no significant differences in demographics, clinical or radiographic parameters, or patient-reported outcomes preoperatively. These results establish a baseline for future work analyzing the outcomes of tether patients and how they compare with the current standard-of-care surgical treatment under a diversity of patient factors with the goal of optimizing care and minimizing risks.


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Demographics and Clinical Factors

VariablePosterior spinal fusion (n=62)Anterior vertebral body tethering (n=20)P
Sex, No..47
  Male8 (13%)4 (20%)
  Female54 (87%)16 (80%)
Race, No..50
  White41 (66%)14 (70%)
  Black8 (13%)4 (20%)
  Other13 (21%)2 (10%)
Age at surgery, mean±SD, y11.7±0.911.8±1.9.83
Height, mean±SD, cm153.2±7.7155.5±12.4.43
Weight, mean±SD, kg47.2±14.246.4±13.8.82
Rib hump thoracic, mean±SD14.7°±4.5°13.8°±4.6°.43
Rib hump lumbar, mean±SD7.3°±4.6°6.1°±2.7°.49
Thoracic/lumbar flexion forward bending, mean±SD, cm10.1±3.39.2±3.4.28
Thoracic/lumbar flexion right bending, mean±SD, cm14.8±5.713.2±4.8.29
Thoracic/lumbar flexion left bending, mean±SD, cm15.5±5.913.8±4.8.25

Radiographic Measures

VariablePosterior spinal fusion (n=62)Anterior vertebral body tethering (n=20)P
Lenke classification curve, No..13
  Type 144 (71%)18 (90%)
  Type 218 (29%)2 (10%)
Lenke classification modifier, No..62
  A49 (79%)18 (90%)
  B12 (19%)2 (10%)
  C1 (2%)0 (0%)
Lenke classification profile, No.a
  Hypo14 (23%)8 (40%).22
  Normal45 (74%)11 (55%)
  Hyper2 (3%)1 (5%)
Thoracic curve, mean±SD50.2°±5.7°51.1°±7.2°.56
Lumbar curve, mean±SD27.0°±6.4°27.0°±6.8°.78
Kyphosis curve, mean±SD18.6°±12.2°18.5°±14.2°.95
Lordosis curve, mean±SD−59.2°±10.5°−57.1°±17.4°.60
Thoracic bend, mean±SD29.6°±12.9°21.3°±10.6°.01
Lumbar bend, mean±SD6.6°±5.4°2.6°±10.3°.12