Curve Evolution During Bracing in Children with Scoliosis Secondary to Early-Onset Neurofibromatosis Type 1: Indicators of Rapid Curve Progression
Introduction
Scoliosis secondary to neurofibromatosis type 1 (NF1) in children under 10 years of age represents a significant subset of early-onset scoliosis (EOS). This condition poses substantial challenges due to its aggressive progression and limited treatment options. While non-fusion surgical techniques, such as growing rods, have been utilized to preserve spinal and pulmonary growth, their associated complications—including infections, implant failure, and repeated surgeries—highlight the need for alternative strategies. Bracing has traditionally been recommended for mild to moderate curves or as a conservative option for patients declining surgery. However, rapid curve progression remains a common issue in NF1-associated EOS, even with strict brace compliance, leading to high rates of treatment failure. This study investigates the natural history of curve evolution during bracing in NF1-associated EOS and identifies risk factors for rapid progression.
Methods
Patient Selection
A retrospective review was conducted on 28 children with NF1-associated EOS who underwent bracing treatment between 2010 and 2017. Inclusion criteria required a confirmed NF1 diagnosis based on Consensus Development Conference criteria, non-dystrophic scoliosis (≤2 dystrophic features) at initial presentation, age 75%, and ≥2 years of follow-up. Exclusion criteria included prior spinal surgery or abnormalities in maturation, height, or lower extremities.
Bracing Protocol
Patients were prescribed a custom thoracolumbosacral orthosis to be worn 22 hours/day. Follow-up visits occurred every 6 months, with adjustments to brace size, wearing time, or weaning decisions based on radiographic progression. Surgical intervention was recommended for curves exceeding 50° with anticipated rapid progression.
Radiographic and Clinical Evaluation
Full-spine radiographs were analyzed at each visit. Key measurements included the Cobb angle of the primary curve, deformity angular ratio (DAR), and dystrophic features (e.g., rib penciling, vertebral rotation, scalloping). Rapid curve progression was defined as an angle velocity (AV) >10°/year. Modulation change—defined as the acquisition of ≥1 dystrophic features during follow-up—was documented, and the age at modulation was recorded.
Statistical Analysis
SPSS software was used for comparisons between rapid progression (AV >10°/year, n=18) and non-rapid progression (n=10) groups. Independent t-tests, chi-square tests, and paired t-tests were applied to assess age, Cobb angle, DAR, and modulation incidence.
Results
Cohort Characteristics
The cohort included 18 females and 10 males with a mean age of 6.5±1.9 years at initial visit. The mean Cobb angle was 41.7°±2.4°, increasing to 67.1°±8.6° over a mean follow-up of 44.1±8.5 months. All patients exhibited curve progression >5°, with 71% (n=20) progressing >20°. Rapid progression (AV >10°/year) occurred in 64% (n=18).
Modulation and Dystrophic Changes
At baseline, 68% (n=19) had 1–2 dystrophic features, while 32% (n=9) had none. During follow-up, 75% (n=21) developed modulation change at a mean age of 8.9±2.1 years. Rib penciling (79%), vertebral wedging (71%), and rotation (68%) were the most common new dystrophic features. All patients with modulation ultimately developed dystrophic curves.
Risk Factors for Rapid Progression
Patients with rapid progression were younger at initial visit (5.6±1.9 vs. 8.1±2.7 years, P=0.008) and had higher modulation incidence (100% vs. 30%, P<0.001). No significant differences were observed in baseline Cobb angle, DAR, or curve type. Among patients with modulation, the AV increased from 4.4°±1.2°/year pre-modulation to 11.8°±2.7°/year post-modulation (P<0.01).
Surgical Outcomes
By the final follow-up, 79% (n=22) underwent posterior spinal fusion at a mean age of 10.3±1.3 years. The remaining six patients continued bracing.
Discussion
Age and Modulation as Critical Indicators
This study underscores the aggressive nature of NF1-associated EOS, with 64% of patients experiencing rapid progression despite bracing. Younger age at initial presentation emerged as a key risk factor, aligning with previous findings in idiopathic scoliosis where skeletal immaturity correlates with progression. Modulation change—particularly the development of rib penciling, vertebral wedging, and rotation—served as a critical marker for transitioning into rapid progression phases. The post-modulation AV of 11.8°/year highlights the clinical urgency to monitor dystrophic changes closely.
Pathophysiological Insights
The transition from non-dystrophic to dystrophic curves reflects underlying NF1 pathology, including osseous dysplasia and connective tissue abnormalities. Rib penciling, a hallmark of dystrophic progression, may destabilize the thoracic cage, exacerbating spinal deformity. Vertebral wedging and rotation further compound biomechanical stress, accelerating curve progression. These findings suggest that modulation is not merely a radiographic phenomenon but a pathophysiological tipping point in NF1-associated scoliosis.
Clinical Implications
Bracing demonstrated limited efficacy in halting progression, as all patients progressed >5°, and 71% exceeded 20°. While bracing may delay surgical intervention, clinicians must educate families about its limitations in NF1-associated EOS. Early surgical consultation is advisable, particularly for younger patients or those developing dystrophic features.
Limitations
The study’s retrospective design, small sample size, and lack of a control group limit generalizability. Additionally, dystrophic features assessed via radiography may underestimate soft tissue abnormalities (e.g., paraspinal tumors) detectable only on MRI or CT.
Conclusion
NF1-associated EOS exhibits aggressive progression during bracing, with younger age and modulation change serving as critical indicators of rapid deterioration. Clinicians should prioritize close monitoring for dystrophic features, as their emergence signals accelerated progression. While bracing remains a temporary measure, early surgical planning is essential to mitigate severe deformity and preserve quality of life.
doi.org/10.1097/CM9.0000000000001606
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