Abstract
Background
To compare the clinical outcomes of posterior spinal fusion (PSF) and traditional growing rod (TGR) surgery for neurofibromatosis type 1-associated dystrophic scoliosis (NF1-DS) in children aged 8–11 years. The aim is also to identify the factors that influence surgical selection and spinal growth.
Methods
Patients with NF1-DS and major thoracic curves involving at least five vertebral levels were enrolled and divided into PSF and TGR groups. Demographic, radiographic and surgical data were analyzed for both a 1:1 propensity score-matched cohort (n = 26) and the full cohort (n = 39). Logistic regression was used to identify factors influencing surgical selection, and Spearman correlation was used to analyze spinal growth predictors.
Results
PSF achieved greater initial curve correction than TGR (61.0% vs. 47.0%, p = 0.025; 58.0% vs. 52.0%, p = 0.015), though there was no difference at the final follow-up. TGR showed greater thoracic (5.2–5.6 cm vs. 3.4–3.5 cm) and spinal height gains (9.0–10.3 cm vs. 4.6–4.9 cm). TGR required more surgeries (5.0 vs. 1.0, p = 0.001), but complication rates were similar. Initial apical vertebra translation (AVT) independently guided surgical selection: PSF for AVT < 46.6 mm and TGR for AVT > 46.6 mm. In the TGR group, greater spinal growth positively correlated with initial curve magnitude, coronal balance, and AVT, while in the PSF group, it positively correlated with the initial main curve correction rate.
Conclusions
This study provides clinical evidence to guide surgical decision-making for 8-11-year-old patients with NF1-DS.
Keywords: Neurofibromatosis type 1, Scoliosis, Traditional growing rod, Posterior spinal fusion
Introduction
Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder that can affect multiple systems [1]. The overall population prevalence is approximately 1/3,164, and the prevalence among live births is 1/2,662 [2]. Spinal deformity, particularly scoliosis, occurs in 30% to 60% of patients with NF1 [3, 4]. The dystrophic type of NF1 scoliosis (NF1-DS) is more prevalent, characterized by spinal curvature accompanied by vertebral scalloping, elongated and attenuated pedicles, rib penciling, and a widened spinal canal and foramen [5]. NF1-DS may also lead to issues such as spinal pain, motor dysfunction, respiratory impairment, and spinal cord nerve injury. These consequences have a huge impact on the quality of life of NF1-DS patients [6, 7].
NF1-DS is characterized by rapid progression, poor response to nonoperative treatments like casting and bracing, and frequent need for surgical intervention [8]. Currently, surgical management for NF1-DS includes traditional growing rod (TGR) techniques and early posterior spinal fusion (PSF), both of which are recommended to prevent progression of the scoliosis [9, 10]. The TGR technique is a common growth-friendly surgery used to treat NF1-DS patients with younger age [11, 12]. The goal of TGR is to correct the curve and allow spinal growth by performing periodic surgical lengthening of the instrumentation until the patient reaches skeletal maturity, at which point a final PSF is usually performed [13, 14]. The advantages of TGR lies in its ability to replicate normal spinal growth, promoting greater spinal height and improved pulmonary function [15]. The limitations of TGR techniques include inadequate fixation strength, the high rate of implant-related complications, and high number of surgeries [16].
For older scoliosis patients with relatively mature skeletal development, PSF surgery is typically used [17, 18]. The PSF technique offers notable advantages by fusing all vertebrae within the main curve through a single surgical procedure, which aims to enhance local spinal internal fixation strength, improve spinal stability, and restore trunk balance [19, 20]. However, PSF surgery may have some limitations, including interference with further spinal height development and impairment of pulmonary function, which can lead to reduced long-term quality of life [21, 22].
However, it should be noted that the majority of the aforementioned findings were based on idiopathic or congenital aetiologies, whereas research on NF1-DS is lacking. In particular, there is no clear consensus on surgical approaches for patients with NF1-DS in the middle age group, such as those aged 8–11 years. Moreover, there is a lack of clarity regarding the factors influencing surgical selection and the impact of different surgical approaches.
Given the rarity of NF1, the present study represents a valuable clinical dataset collected at Beijing Children’s Hospital, Capital Medical University. Between June 2007 and June 2022, a total of 174 patients with NF1-DS underwent surgical treatment. After strict inclusion and exclusion criteria were applied, 39 patients aged 8 to 11 years at the time of surgery were eligible for analysis. The primary aims of this study were to: (1) evaluate and compare the impact of PSF and TGR surgery on spinal development and clinical outcomes; (2) identify preoperative indicators that guide the selection of surgical strategies; and (3) identify the factors that influence spinal growth in TGR and PSF.
Materials and methods
Patient selection and categorization
Between June 2007 and June 2022, patients diagnosed with NF1-associated dystrophic scoliosis (NF1-DS) who presented to Beijing Children’s Hospital for surgical treatment were screened for eligibility. A total of 174 patients with NF1-DS underwent surgical treatment. Inclusion criteria were as follows: (1) diagnosis of NF1-DS [23]; (2) age between 8 and 11 years at the time of initial surgery; (3) presence of a major thoracic curve; and (4) the major curve involving ≥ 5 vertebral levels. Exclusion criteria included: (1) presence of cervical deformities alone; (2) incomplete clinical or radiographic data; (3) follow-up duration of less than 2 years; and (4) patients who underwent TGR (traditional growing rod) but did not proceed to definitive PSF (posterior spinal fusion). After applying strict inclusion and exclusion criteria, 39 patients (22 males, 17 females) aged 8 to 11 years at surgery were eligible for analysis, defined as the full cohort. A propensity score-matched cohort comprising 13 pairs (26 patients, 17 males and 9 females) was constructed using a 1:1 matching method. The specific matching process is detailed in the Statistical Analysis section.
Patients were categorized into two groups according to their initial surgical procedure: the PSF group and the TGR group. The surgical plan for each patient was developed through the following three steps: (1) First, a comprehensive case discussion was conducted at the Department of Orthopedics, Beijing Children’s Hospital. The patient’s demographic information, clinical symptoms, physical examination findings, growth potential, and spinal imaging results were reviewed to formulate a preliminary surgical plan. (2) Second, the surgical plan was further evaluated and finalized by at least three spine surgeons, each with more than 10 years of surgical experience. This included determining the surgical approach, the placement of pedicle screws, the selection of upper and lower instrumented vertebrae, and the extent of spinal fusion. (3) Finally, detailed preoperative counseling was provided to the patient’s family, including a thorough explanation of the surgical objectives, techniques, expected benefits, and potential risks. The final surgical plan was confirmed after obtaining informed consent from the family.
This study was conducted in accordance with the principles of the Declaration of Helsinki. Ethical approval was obtained from the Institutional Review Board of Beijing Children’s Hospital (Code: 2022-E-083-R), and written informed consent was obtained from the parents or legal guardians of all participants.
Data collection
Firstly, we collected demographic information, including age at surgery, body mass index (BMI), status of the triradiate cartilage, Risser sign, and vertebrae involved in the main curve. Secondly, we collected radiographic data involved in main curve Cobb angle, apical vertebra translation, coronal and sagittal balance, thoracic height (measured from the superior endplate of T1 to the inferior endplate of T12 in the coronal plane), and spinal height (measured from the superior endplate of T1 to the superior endplate of S1 in the coronal plane). The vertebral dystrophic changes, dislocated ribs and pedicle thinning were recorded based on CT scans. The diagnostic criterion for vertebral dystrophic changes is a thoracic vertebral depression depth of ≥ 3 mm or a lumbar vertebral depression depth of ≥ 4 mm on the coronal or sagittal plane of CT images. For pedicle thinning, the diagnostic criterion is a narrowest pedicle width of ≤ 2 mm at the widest cross-section of the apical vertebral pedicle in CT scans. The presence of paravertebral NF-related tumors was documented based on MRI scans. Thirdly, surgical outcomes data were gathered, involving the number of surgeries, instrumented vertebral levels, main curve correction rate, ΔT1-T12 Height, ΔT1-S1 Height, ΔT1-T12% Gain, ΔT1-S1% Gain, and the incidence of surgery-related complications, which were defined as screw dislodgement, cap loosening, rod breakage, junctional kyphosis, adding-on phenomenon, pedicle cutting, curve progression, crankshaft phenomenon, or trunk shift. For patients who underwent TGR, additional data such as the number of distraction procedures, intervals between lengthening, and the final transition to PSF were also collected.
Follow-up protocol
At each visit, standing anteroposterior and lateral radiographs of the entire spine were obtained. PSF group: Follow-up at 3-, 6-, and 12-months post-surgery, then annually. TGR group: Follow-up evaluations every 6 months post-surgery, with lengthening intervals of 6–12 months. Indications for transitioning from TGR to definitive PSF include: (1) Age: ≥14 years for females and ≥ 16 years for males; (2) Risser sign 4–5 and closure of the triradiate cartilage; (3) Spinal growth rate < 1 cm/year and distraction gain < 1 cm per procedure; and (4) Cobb angle ≤ 20° with no progression observed during 6–12 months of follow-up.
Statistical analysis
Comparison of surgical outcomes between TGR and PSF surgeries
To compare intergroup differences in surgical outcomes, we employed two cohorts for analysis. The first cohort involved a case-matched outcome comparison (n = 26). To minimize selection bias and ensure baseline comparability, 1:1 propensity score matching was performed between the PSF and TGR groups. The matching criteria included: (1) preoperative age was matched within ± 18 months to synchronize skeletal maturity stages among patients; (2) major curve magnitude was aligned within ± 10° to balance the severity of spinal deformities; and (3) apical vertebra location was standardized within ± 2 vertebral levels to account for variations in curve topography. The second cohort comprised the full NF1-DS cohort outcome comparison (n = 39).
We compared intergroup differences in demographics, preoperative and postoperative parameters, final follow-up outcomes, surgical efficacy, number of surgeries, and surgery-related complications between children in the TGR and PSF groups. The Shapiro-Wilk test was employed to assess the normality of continuous data. Clinical and radiographic variables between groups were compared using the student t-test or Mann-Whitney U test for continuous data and the chi-square (χ2) test or Fisher’s exact test for categorical data. Categorical data were presented as frequencies, rates, or proportions. A significance level of p < 0.05 was considered statistically significant.
Indicators of surgical approach selection
A binary logistic regression model was developed within the full NF1-DS cohort (n = 39) to determine independent indicators for surgical approach selection. Univariate screening of preoperative variables was performed first. The variables included age, sex, number of vertebrae in the main curve, main curve Cobb angle, T1-T12 height, T1-S1 height, coronal balance, sagittal balance and AVT. Variables with limited clinical relevance or a p-value greater than 0.100 were excluded, and the remaining variables were then subjected to binary logistic regression.
The regression model was refined by iteratively incorporating significant predictors using the enter method. Model validation involved assessing goodness of fit using the Hosmer–Lemeshow test (where p > 0.05 indicates adequacy) and evaluating predictive efficacy through ROC curve analysis. An AUC of at least 0.7 was deemed clinically significant. Critical values for selecting a surgical approach were then derived by integrating the results of the regression equation and the ROC curve cutoffs.
Correlation analysis of spinal parameters in TGR and PSF
Finally, we conducted a Spearman correlation analysis to analyze the influencing factors associated with spinal parameters, and screened the related factors affecting spinal height increase and spinal height increase rate.
All statistical analyses were conducted using SPSS 26.0 for Windows (SPSS Inc., Chicago, IL).
Results
Comparison of surgical outcomes between TGR and PSF surgeries
Following 1:1 propensity score matching, 13 pairs of TGR and PSF patients were analyzed (Table 1). The PSF group achieved significantly greater initial curve correction than the TGR group (61.0% vs. 47.0%, p = 0.025). At the latest follow-up, no significant intergroup differences in curve correction were observed between the PSF and TGR groups (63.0% vs. 67.0%, p = 0.727). At the latest follow-up, the TGR group showed significantly greater thoracic height gain (5.2 cm vs. 3.4 cm, p = 0.026) and percentage of gain (29.0% vs. 17.0%, p = 0.019). Cumulative spinal height growth was also markedly higher in the TGR group (9.0 cm vs. 4.9 cm, p = 0.007), along with a significantly greater percentage of gain (32.0% vs. 14.0%, p = 0.007).
Table 1.
Radiographic data of 26 NF1-DS patients (One-to-one matched cohort)
| TGR Group(n = 13) | PSF Group(n = 13) | Z/χ2 Value | P | |
|---|---|---|---|---|
| Demographics | ||||
| Age (Years), M (Q1, Q3) | 9.1 (8.6, 9.4) | 9.0 (8.7, 10.0) | -0.839 | 0.401 |
| Sex (Male), N (%) | 9.0 (69.2%) | 8.0 (61.5%) | - | 1.000 |
| Triradiate Cartilage (Open), N (%) | 13.0 (100.0%) | 13.0 (100.0%) | - | - |
| Risser Sign (Grade 0), N (%) | 13.0 (100.0%) | 13.0 (100.0%) | - | - |
| Body Mass Index (kg/m²) | 15.9 (14.9, 16.7) | 16.0 (15.2, 17.4) | -0.669 | 0.503 |
| Vertebrae in Main Curve, N | 11.0 (9.5, 11.5) | 10.0 (9.5, 10.5) | -1.656 | 0.098 |
| Vertebral Dystrophic Changes, N (%) | 13.0 (100.0%) | 13.0 (100.0%) | - | - |
| Pedicle Thinning, N (%) | 12.0 (92.3%) | 11.0 (84.6%) | - | 1.000 |
| Dislocated Ribs, N (%) | 4.0 (30.1%) | 3.0 (23.1%) | - | 1.000 |
| Paravertebral Tumor, N (%) | 9.0 (69.2%) | 8.0 (61.5%) | - | 1.000 |
| Preoperative, M (Q1, Q3) | ||||
| Main Curve Cobb Angle (°) | 62.0 (55.0, 84.0) | 57.0 (53.5, 79.5) | -1.739 | 0.082 |
| T1-T12 Height (cm) | 17.5 (15.8, 20.6) | 19.9 (17.2, 21.8) | 1.573 | 0.116 |
| T1-S1 Height (cm) | 30.0 (27.5, 32.5) | 32.6 (29.7, 35.0) | 1.642 | 0.101 |
| Coronal Balance (mm) | 15.2 (8.5, 32.3) | 17.0 (10.5, 20.0) | 0.078 | 0.937 |
| Sagittal Balance (mm) | 24.0 (15.5, 40.5) | 30.0 (12.5, 46.0) | 0.734 | 0.463 |
| Apical Vertebra Translation (mm) | 51.0 (34.5, 81.0) | 35.0 (26.5 (45.0) | -2.132 | 0.033 * |
| Postoperative, M (Q1, Q3) | ||||
| Main Curve Cobb Angle (°) | 30.0 (22.0, 43.5) | 20.0 (9.5, 33.0) | -2.308 | 0.021 * |
| T1-T12 Height (cm) | 21.0 (19.0, 21.9) | 22.5 (19.5, 23.3) | 1.139 | 0.255 |
| T1-S1 Height (cm) | 33.2 (31.3, 36.1) | 36.5 (32.5, 38.3) | 1.060 | 0.289 |
| Coronal Balance (mm) | 9.0 (5.0, 15.0) | 10.0 (3.5, 16.5) | 0.245 | 0.806 |
| Sagittal Balance (mm) | 15.0 (8.0, 22.0) | 10.0 (9.0, 18.5) | -0.350 | 0.727 |
| Apical Vertebra Translation (mm) | 16.0 (14.5, 38.0) | 15.0 (8.5, 18.5) | -2.377 | 0.017 * |
| Latest Follow-up, M (Q1, Q3) | ||||
| Main Curve Cobb Angle (°) | 20.0 (16.5, 30.5) | 11.0 (8.5, 33.0) | -0.595 | 0.552 |
| T1-T12 Height (cm) | 24.0 (19.8, 25.6) | 23.4 (21.0, 24.4) | -0.392 | 0.695 |
| T1-S1 Height (cm) | 40.0 (36.0, 41.4) | 36.7 (34.7, 40.1) | -1.398 | 0.162 |
| Coronal Balance (mm) | 8.0 (5.0, 11.0) | 7.0 (2.0, 10.8) | -0.490 | 0.624 |
| Sagittal Balance (mm) | 18.0 (12.0, 22.0) | 10.0 (7.0, 15.5) | -1.414 | 0.157 |
| Apical Vertebra Translation (mm) | 10.0 (5.0, 22.0) | 15.0 (10.0, 25.5) | 1.504 | 0.133 |
*Indicates statistically significant comparison with P value less than or equal to 0.05. NF1-DS dystrophic scoliosis associated with neurofibromatosis type 1, TGR traditional growing rod, PSF posterior spinal fusion, M median, Q1 first quartile, Q3 third quartile, FU follow-up, Preop preoperative; Postop, postoperative
The TGR group required significantly more surgeries compared to the PSF group (5.0 vs. 1.0, p = 0.001). TGR patients had a total of 76 surgical procedures including initial surgeries (13), lengthenings (47), unplanned revisions (3), and final fusions (13). PSF patients had 15 surgical procedures, comprising 13 index fusion procedures and 2 unplanned revisions. In the TGR group, 3 cases of rod breakage occurred after surgery; in the PSF group, 2 cases of adding-on phenomenon occurred after surgery. No significant difference in complication rates was observed between the groups (Table 2).
Table 2.
Increased height of spine and surgical outcomes of 26 NF1-DS patients (One-to-one matched cohort)
| TGR Group(n = 13) | PSF Group(n = 13) | Z/χ2 Value | P | |
|---|---|---|---|---|
| Postoperative, M (Q1, Q3) | ||||
| Instrumented Vertebrae Levels, N | 13.0 (11.5, 13.5) | 12.0 (12.0, 12.5) | -1.127 | 0.260 |
| Initial Main Curve Correction (%) | 47.0 (45.0, 60.0) | 61.0 (53.5, 82.5) | 2.237 | 0.025 * |
| ΔT1-T12 Height (Postop - Preop) (cm) | 2.6 (1.4, 3.5) | 2.6 (0.7, 3.7) | 0.175 | 0.861 |
| ΔT1-S1 Height (Postop - Preop) (cm) | 3.1 (2.1, 4.1) | 4.2 (3.2, 4.5) | 1.364 | 0.173 |
| ΔT1-T12 % Gain (Postop - Preop) (%) | 9.5 (4.6, 16.0) | 13.1 (7.0, 20.3) | 0.734 | 0.463 |
| ΔT1-T12 % Gain (Postop - Preop) (%) | 8.3 (6.9, 13.4) | 12.7 (9.4, 17.0) | 1.503 | 0.133 |
| Latest Follow-up, M (Q1, Q3) | ||||
| Overall Main Curve Correction (%) | 67.0 (55.0, 77.5) | 63.0 (53.5, 86.0) | -0.350 | 0.727 |
| ΔT1-T12 Height (Last FU - Preop) (cm) | 5.2 (2.3, 7.7) | 3.4 (2.5, 4.0) | -2.225 | 0.026 * |
| ΔT1-S1 Height (Last FU - Preop) (cm) | 9.0 (5.6, 12.3) | 4.9 (3.5, 6.8) | -2.691 | 0.007 * |
| ΔT1-T12 % Gain (Last FU - Preop) (%) | 29.0 (13.0, 47.0) | 17.0 (13.5, 23.5) | -2.341 | 0.019 * |
| ΔT1-S1 % Gain (Last FU - Preop) (%) | 32.0 (17.5, 45.0) | 14.0 (11.0, 21.5) | -2.714 | 0.007 * |
| FU Duration (years), M (Q1, Q3) | 4.1 (3.9, 5.4) | 4.0 (3.4, 5.5) | -0.218 | 0.827 |
| Number of Surgeries, M (Q1, Q3) | 5.0 (4.0, 6.0) | 1.0 (1.0, 1.0) | -3.209 | 0.001 * |
| Number of Complications, N (%) | 3.0 (23.1%) | 2.0 (15.4%) | - | 1.000 |
*Indicates statistically significant comparison with P value less than or equal to 0.05. NF1-DS dystrophic scoliosis associated with neurofibromatosis type 1, TGR traditional growing rod, PSF posterior spinal fusion, M median, Q1 first quartile, Q3 third quartile, FU follow-up, Preop preoperative, Postop postoperative
To further enhance the statistical power, we performed analyses using the entire NF1-DS cohort (n = 39). There were 18 cases in the TGR group and 21 cases in the PSF group. In the TGR group, 4 cases of growing rod breakage and 1 case of cap loosening occurred after surgery; in the PSF group, 2 cases of adding-on phenomenon, 2 cases of junctional kyphosis, and 1 case of trunk shift occurred after surgery. Significantly, all outcome metrics showed full consistency with the results obtained from the 1:1 propensity score matching analysis (n = 26), as detailed in Tables 3 and 4.
Table 3.
Radiographic data of 39 NF1-DS patients (Full cohort)
| TGR Group(n = 18) | PSF Group(n = 21) | Z/χ2 Value | P | |
|---|---|---|---|---|
| Demographics | ||||
| Age (Years), M (Q1, Q3) | 9.2 (8.7, 9.8) | 9.7 (8.8, 10.5) | 0.923 | 0.364 |
| Sex (Male), N (%) | 12.0 (66.7%) | 10.0 (47.6%) | - | 1.000 |
| Triradiate Cartilage (Open), N (%) | 18.0 (100.0%) | 21.0 (100.0%) | - | - |
| Risser Sign (Grade 0), N (%) | 18.0 (100.0%) | 21.0 (100.0%) | - | - |
| Body Mass Index (kg/m²) | 15.6 (14.6, 16.4) | 16.0 (14.9, 17.0) | -0.591 | 0.555 |
| Vertebrae in Main Curve, N | 10.0 (8.0, 13.0) | 9.0 (7.0, 10.0) | -1.556 | 0.130 |
| Vertebral Dystrophic Changes, N (%) | 18.0 (100.0%) | 21.0 (100.0%) | - | - |
| Pedicle Thinning, N (%) | 16.0 (88.9%) | 18.0 (85.7%) | - | 1.000 |
| Dislocated Ribs, N (%) | 6.0 (33.3%) | 6.0 (28.6%) | 0.103 | 0.748 |
| Paravertebral Tumor, N (%) | 13.0 (72.2%) | 15.0 (71.4%) | 0.003 | 0.956 |
| Preoperative, M (Q1, Q3) | ||||
| Main Curve Cobb Angle (°) | 59.5 (51.3, 83.0) | 64.0 (54.5, 74.5) | 1.143 | 0.253 |
| T1-T12 Height (cm) | 19.4 (15.7, 20.5) | 20.0 (17.7, 22.0) | 1.295 | 0.200 |
| T1-S1 Height (cm) | 31.0 (27.8, 32.9) | 33.4 (29.4, 36.1) | 1.867 | 0.065 |
| Coronal Balance (mm) | 21.5 (9.0, 4.5) | 20.0 (10.5, 25.0) | -0.551 | 0.581 |
| Sagittal Balance (mm) | 18.5 (16.0, 30.3) | 23.0 (10.0, 40.0) | 0.085 | 0.932 |
| Apical Vertebra Translation (mm) | 55.0 (35.0, 79.0) | 38.0 (23.5, 44.0) | -3.147 | 0.002 * |
| Postoperative, M (Q1, Q3) | ||||
| Main Curve Cobb Angle (°) | 28.0 (21.0, 43.3) | 30.0 (10.5, 33.0) | 1.414 | 0.157 |
| T1-T12 Height (cm) | 21.1 (19.7, 22.0) | 22.8 (20.0, 23.3) | 1.324 | 0.198 |
| T1-S1 Height (cm) | 34.5 (31.8, 36.3) | 36.9 (32.5, 39.2) | 1.176 | 0.244 |
| Coronal Balance (mm) | 9.5 (5.8, 15.0) | 11.0 (3.5, 17.0) | 0.367 | 0.713 |
| Sagittal Balance (mm) | 12.0 (9.0, 20.0) | 15.0 (9.0, 19.5) | 0.099 | 0.921 |
| Apical Vertebra Translation (mm) | 21.5 (14.8, 32.0) | 16.0 (8.5, 23.0) | -1.936 | 0.053 |
| Latest Follow-up, M (Q1, Q3) | ||||
| Main Curve Cobb Angle (°) | 19.0 (9.0, 27.8) | 27.0 (8.5, 30.0) | 0.127 | 0.900 |
| T1-T12 Height (cm) | 24.0 (21.2, 25.7) | 23.4 (22.0, 24.6) | -0.834 | 0.372 |
| T1-S1 Height (cm) | 40.2 (36.9, 41.6) | 37.5 (35.0, 40.1) | -1.432 | 0.169 |
| Coronal Balance (mm) | 8.0 (5.0, 10.0) | 7.0 (2.0, 13.0) | -0.227 | 0.821 |
| Sagittal Balance (mm) | 14.5 (12.0, 20.0) | 10.0 (5.5, 16.0) | -0.621 | 0.534 |
| Apical Vertebra Translation (mm) | 15.0 (6.5, 24.3) | 16.0 (5.0, 21.0) | -1.886 | 0.051 |
* Indicates statistically significant comparison with P value less than or equal to 0.05. NF1-DS dystrophic scoliosis associated with neurofibromatosis type 1, TGR traditional growing rod, PSF posterior spinal fusion, M median, Q1 first quartile, Q3 third quartile, FU follow-up, Preop preoperative, Postop postoperative
Table 4.
Increased height of spine and surgical outcomes of 39 NF1-DS patients (Full cohort)
| TGR Group(n = 18) | PSF Group(n = 21) | Z/χ2 Value | P | |
|---|---|---|---|---|
| Postoperative, M (Q1, Q3) | ||||
| Instrumented Vertebrae Levels, N | 12.0 (10.0, 15.0) | 11.0 (10.0, 12.0) | -1.510 | 0.142 |
| Initial Main Curve Correction (%) | 52.0 (45.0, 59.0) | 58.0 (54.0, 80.5) | 2.432 | 0.015 * |
| ΔT1-T12 Height (Postop - Preop) (cm) | 3.0 (1.4, 4.6) | 3.1 (2.0, 3.8) | 0.522 | 0.601 |
| ΔT1-S1 Height (Postop - Preop) (cm) | 4.0 (2.6, 4.9) | 4.4 (3.3 ,5.2) | 0.635 | 0.525 |
| ΔT1-T12 % Gain (Postop - Preop) (%) | 16.2 (9.5, 20.6) | 19.0 (7.9, 24.2) | 0.080 | 0.933 |
| ΔT1-T12 % Gain (Postop - Preop) (%) | 12.5 (7.9, 16.4) | 15.5 (9.5,19.0) | 1.438 | 0.150 |
| Latest Follow-up, M (Q1, Q3) | ||||
| Overall Main Curve Correction (%) | 65.3 (55.0, 84.8) | 58.0 (55.0, 86.0) | -0.352 | 0.745 |
| ΔT1-T12 Height (Last FU - Preop) (cm) | 5.6 (3.0, 7.6) | 3.5 (2.2, 4.1) | -2.066 | 0.041 * |
| ΔT1-S1 Height (Last FU - Preop) (cm) | 10.3 (6.9, 11.7) | 4.6 (3.4, 6.6) | -3.167 | 0.001 * |
| ΔT1-T12 % Gain (Last FU - Preop) (%) | 32.1 (15.6, 42.7) | 17.0 (12.0, 22.1) | -2.622 | 0.009 * |
| ΔT1-S1 % Gain (Last FU - Preop) (%) | 32.0 (22.0, 43.5) | 14.0 (10.0, 21.0) | -3.071 | 0.002 * |
| FU Duration (years), M (Q1, Q3) | 4.0 (3.7, 5.3) | 4.0 (3.4, 5.7) | 0.372 | 0.710 |
| Number of Surgeries, M (Q1, Q3) | 5.0 (4.5, 6.5) | 1.0 (1.0, 1.5) | -4.657 | 0.001* |
| Number of Complications, N (%) | 5.0 (27.8%) | 5.0 (23.8%) | - | 1.000 |
*Indicates statistically significant comparison with P value less than or equal to 0.05. NF1-DS dystrophic scoliosis associated with neurofibromatosis type 1, TGR traditional growing rod, PSF posterior spinal fusion, M median, Q1 first quartile, Q3 third quartile, FU follow-up, Preop preoperative, Postop postoperative
Indicators of surgical approach selection
Following univariate screening, variables such as sex (p = 1.000), vertebrae in main curve (p = 0.130), main curve Cobb angle (p = 0.253), T1-T12 height (p = 0.200), coronal balance (p = 0.581), and sagittal balance (p = 0.932) were excluded due to significance levels far exceeding 0.100. Notably, T1-S1 height (p = 0.065) and AVT (p = 0.002) were included in the binary logistic regression analysis, with age (p = 0.364) serving as a covariate.
The binary logistic regression was overall significant (χ² = 16.335, df = 3, p = 0.001). The Hosmer-Lemeshow test indicated a good fit (χ² = 10.246, df = 7, p = 0.175). The − 2 log-likelihood value was 37.500, Cox & Snell R² was 0.342, Nagelkerke R² was 0.457, and the overall prediction accuracy of the model was 66.7%.
The model revealed that initial AVT was an effective indicator of spinal surgery approaches [B = -0.057, SE = 0.027, Wald = 4.437, p = 0.035, Exp (B) = 0.944]. Initial spinal height had no significant effect on the selection of surgical methods. Threshold analysis derived from the predictive model identified 46.6 mm as the critical AVT cutoff. PSF was preferred for cases with an AVT < 46.6 mm, while an AVT > 46.6 mm indicated a tendency toward TGR surgery.
Correlation analysis of spinal parameters in TGR and PSF
In the TGR group, the analysis revealed that the final spinal height increase was positively correlated with the main curve range (r = 0.553, p = 0.017), initial coronal balance (r = 0.569, p = 0.014), and initial AVT (r = 0.569, p = 0.014). Concurrently, the final spinal height increase rate showed a positive correlation with the main curve range (r = 0.744, p < 0.001), initial coronal balance (r = 0.515, p = 0.029), and initial AVT (r = 0.728, p < 0.001).
In the PSF group, correlation analysis indicated a positive association between the final spinal height increase and the main curve correction rate at final follow-up (r = 0.606, p = 0.004). Additionally, the final spinal height increase rate exhibited a comparable positive correlation with the main curve correction rate at final follow-up (r = 0.460, p = 0.036), as detailed in Table 5.
Table 5.
Correlation analysis of spinal parameters in TGR and PSF
The gray area represents the parameters of TGR surgery, and the blue represents the parameters of PSF surgery
TGR traditional growing rod, PSF posterior spinal fusion, AVT apical vertebra translation
* Indicates statistically significant comparison with P value less than or equal to 0.05
** Indicates statistically significant comparison with P value less than or equal to 0.01
*** Indicates statistically significant comparison with P value less than or equal to 0.001
Discussion
Previous studies have not reached a consensus on the optimal surgical approach for 8-11-year-old NF1-DS patients. This study showed that the PSF achieved higher immediate major curve correction than the TGR, though both groups showed similar correction rates (~ 60%) at the last follow-up. The TGR group demonstrated significantly greater spinal height gain (4 cm more) but required 4 additional surgical procedures, with no significant difference in complication rates between groups. AVT was identified as an effective indicator for surgical selection: PSF was preferred for AVT < 46.6 mm, while TGR was more suitable for AVT > 46.6 mm. In the TGR group, greater spinal growth positively correlated with initial curve magnitude, coronal balance, and AVT, while in the PSF group, it positively correlated with the initial main curve correction rate.
According to previous literature, the correction rate of the main curve Cobb angle for PSF ranges from 55% to 59%, whereas for TGR, it ranges from 37% to 42% [24–27]. The improved correction rate observed in PSF is primarily attributed to the increased density of internal fixation and the option for posterior column osteotomy during surgery [28–30]. In contrast, TGR achieves indirect correction of the primary curve deformity by exerting longitudinal distraction forces on the curve, leading to a comparatively lower correction rate [31, 32]. However, some studies had relatively short follow-up times, and not all patients receiving TGR underwent final fusion surgery, which could have influenced the reported correction rates. In our study, all children who underwent TGR had subsequently undergone PSF, which further improved the main curve correction rate. Patients with NF1-DS typically exhibit abnormal bone metabolism and impaired osteoblast function [33–35]. Spontaneous spinal fusion following TGR surgery is relatively uncommon, this ensures that each distraction surgery is effective. For patients undergoing TGR, regular and adequate distraction procedures combined with final fusion surgery contribute to sustained correction of spinal deformity and achieve satisfactory correction rates for NF1-DS patients [36, 37].
The TGR technique can control spinal deformity and maximize spinal height. Jain et al. reported a study involving 14 patients with NF1-associated scoliosis who underwent TGR at an average age of 6.8 years, these patients experienced an average annual increase in spinal height of 1.1 cm [38]. Cai et al. found that the annual increase in spinal height in the TGR group was higher than in the PSF group [(11.7 ± 2.6) mm/year vs. (5.6 ± 1.7) mm/year, p < 0.05] [39]. Similarly, Tauchi et al. reported that in NF1 spinal deformity patients, TGR achieved a 33.9% increase in spinal height, while PSF only achieved a 19% increase, which was statistically significant [40]. This study also found that the TGR group had greater increases in spinal height compared to the PSF group. This finding indicates that for NF1 scoliosis patients aged 8 to 11 with a main curve involving ≥ 5 vertebral levels, TGR can further increase spinal height, which is more conducive to spinal growth in this age group compared to PSF.
According to previous literature, the incidence of surgery-related complications and the number of surgeries is significantly lower in PSF compared to TGR. Carbone et al. reported on 7 cases of NF1 scoliosis patients undergoing TGR, with an average of 5.3 distraction surgeries, of which 4 cases (57%) experienced complications [27]. Bouthors et al. reported on 18 cases of NF1-DS treated with TGR, with an average of 3 distraction surgeries, and a surgery-related complications rate of 72%. Conversely, for patients undergoing PSF, the average surgical frequency ranges from 1.0 to 2.6 surgeries, with a surgery-related complications rate between 5.2% and 20.0% [26]. Additionally, Yao et al. identified the use of TGR as an independent risk factor for surgery-related complications [41]. TGR’s lower internal fixation density and frequent pre-fusion distractions may account for its higher complication rate. However, there were no significant differences in the incidence of complications between the TGR and PSF groups in our study. The TGR group is more prone to instrumentation-related complications, such as growing rod breakage and cap loosening, which may be attributed to lower internal fixation density and a greater number of surgical procedures. In contrast, the PSF group—due to earlier spinal fusion—is more likely to develop non-instrumentation-related complications, including adding-on phenomenon, junctional kyphosis, and trunk shift. The targeted therapies such as selumetinib are expected to improve bone quality and enhance comprehensive treatment outcomes for children with NF1-DS [35].
In previous clinical practice, In previous clinical practice, Pawelek JB et al. conducted a comparative study of TGR and SF surgeries in 22 patients with adolescent idiopathic scoliosis aged 9–11 years [42]. Keil LG et al. performed a comparative study of TGR and SF surgeries in 50 patients with early-onset scoliosis aged 7–11 years [43]. Despite these efforts, no clear consensus has been reached on surgical approaches for patients with NF1-DS in the middle age group. Instead, the choice relied more on the surgeon’s experience and the patient’s comprehensive conditions. Insufficient attention was paid to how specific indicators influence surgical approach selection. This study confirms that AVT is an independent predictive factor affecting the selection of surgical techniques. TGR surgery is preferred when AVT exceeds 46.6 mm, as a larger AVT often indicates more severe spinal deformities, such as significant trunk imbalance, increased apical vertebra rotation and spinal cord deviation towards the concave side [44, 45]. This leads to a significantly higher risk of screw placement in the apical vertebra region. The TGR technique reduces the risk of nerve injury and internal fixation failure during the initial surgery, while also regulating spinal growth to achieve satisfactory corrective outcomes [46, 47]. Conversely, a small AVT indicates relatively mild spinal deformity, accompanied by a lower risk of screw placement in the apical vertebra. The PSF procedure enables ideal three-dimensional correction in a single operation, while avoiding the complications of multiple surgeries and implant fractures associated with the TGR technique [48, 49]. It is worth noting that, although AVT provides a quantitative basis for surgical decision-making in NF1-DS, its critical value still needs to be verified in large, multi-center studies. In clinical practice, a comprehensive approach should be taken, combining factors such as the patient’s age, sex, height, skeletal maturity, overall health and family income.
The effect of TGR surgery on increasing spinal height is partially dependent on the preoperative anatomical structure of the spine. Preoperative evaluation of parameters including the main curve range, coronal balance, and AVT may provide a useful reference for estimating the extent of spinal height increase following TGR surgery [50, 51]. A larger main curve range is associated with more significant spinal height increase achieved through growing rod distraction surgery, possibly because a greater curve range indicates better flexibility of the spinal deformity, providing more space for longitudinal growth. Moreover, continuous distraction procedures gradually correct coronal balance and AVT, where a larger preoperative offset provides a structural basis for the gradual increase in spinal height. Unlike TGR, PSF surgery restricts spinal growth potential due to fusion and fixation, so the height increase relies more on immediate intraoperative orthopedic effects rather than postoperative growth [48, 52]. Therefore, improving the main curve correction rate during the PSF surgery is crucial for enhancing spinal height in 8-11-year-old NF1-DS patients.
Our findings have several limitations. First, although propensity score matching was used to reduce selection bias, the retrospective design of this study persists as a limitation. Non-randomized decision-making may introduce unmeasured confounders, thereby constraining causal inferences from the analysis. Second, the study included a relatively small sample size, particularly in the matched cohort (n = 26), which limits both statistical power and the generalizability of the findings. Third, only two growth and maturity indicators (Risser sign and status of the triradiate cartilage) were considered in our study. The Sanders Maturity Score (SMS) should have been included to improve comprehensiveness, and the lack of SMS also means we were unable to specifically address the “Tweener” population—a group with intermediate skeletal maturity that is clinically relevant but not captured by our current indicator set. Finally, the study focused primarily on radiographic and surgical outcomes; health-related quality of life measures and pulmonary function data were unavailable for comparative analysis. Future studies will incorporate quality of life scores and pulmonary function tests to enhance research depth and clinical relevance, while advocating for larger multi-center cohorts with expanded samples to validate and extend our findings. We will also explicitly integrate the SMS to better characterize skeletal maturity—including the “Tweener” subgroup—and strengthen the robustness of our analyses.
Conclusions
In 8-11-year-old NF1-DS patients, PSF and TGR demonstrated comparable main curve correction rates and complications, with TGR promoting approximately 4 cm more spinal height growth than PSF but requiring 4 additional surgeries. Initial AVT served as the independent indicator for surgical approach. In TGR, preoperative main curve range, coronal balance, and AVT influenced final spinal height gain, while in PSF, optimizing the initial main curve correction rate was key to spinal height enhancement. This study enhances clinical understanding and informs surgical management strategies for children aged 8 to 11 with NF1-DS.
Acknowledgements
We would like to thank Dr. Tianyuan Lei for her assistance in the statistical methods of this article.
Authors’ contributions
Haichong Li and Hanwen Zhang: conceptualization, writing–original draft, writing–review and editing, patient management and literature review; Ziming Yao and Xuejun Zhang: supervision, editing of the manuscript, critical appraisal, and final approval of the manuscript; Rongxuan Gao, Haonan Liu, Dong Guo and Jun Cao: writing–review and editing, patient management, and literature review. All authors have finally confirmed and reviewed the manuscript content.
Funding
This study was supported by Key R&D Program of Xinjiang (2023 B03018-2), National Key R&D Program of China (2023YFC2507701).
Data availability
The data used during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study was conducted in accordance with the principles of the Declaration of Helsinki. Ethical approval was obtained from the Institutional Review Board of Beijing Children’s Hospital, and written informed consent was obtained from the parents or legal guardians of all participants.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data used during the current study are available from the corresponding author on reasonable request.