Subclassification of Sanders Stage 7: The use of ulna physis can improve decision-making for brace weaning in adolescent idiopathic scoliosis

Abstract

Introduction: Adolescent idiopathic scoliosis(AIS) is a three-dimensional deformity which progresses rapidly during pubertal growth spurt and stablizes near skeletal maturity. Previous studies found that curve progression can occur if bracing is weaned at Sanders stage (SS) 7 which represents the early mature stage. A wide range of radiographic appearance occurs from open to fusion of the distal radius and ulna physis between SS7 and SS8. This warrants the investigation of whether subclassification of SS7 allows more accurate identification of skeletal maturity that can lead to an earlier and safe timing for brace weaning. The distal radius and ulna (DRU) classification utilizes the radiographic appearance of the distal radius and ulna comprehensively, and gradings are readily available for assessing decelerating growth and growth cessation. This study aims to investigate whether including the stages of ulnar physeal closure in SS7 aids in more accurate maturity assessment for brace weaning in AIS. Materials and Methods: This was a retrospective analysis of AIS patients at a specialist clinic from June 2016 to Decemeber 2018. Patients who weaned brace-wear at Risser stage ≥4, static standing body height and arm span for at least 6 months and ≥2 years post-menarche were included. Skeletal maturity at weaning was assessed using DRU classification and Sanders staging with SS7 subclassified into SS7a (all phalangeal physes are fused and only distal radial physes are open, with narrowing of medial physeal plate of the distal ulna) and SS7b (those with >50% fusion of the medial growth plate of distal ulna). The relationship of weaning maturity grading and any curve progression was analyzed using Fisher’s exact test, with Cramer’s V and Goodman and Kruskal’s tau. Results: A total of 179 AIS patients (83.2% females) were studied with mean age of 14.8 ± 1.1 years and Cobb angle of 34.6 ± 7.7° at weaning. Follow-up period was 3.4 ± 1.8 years. At post-weaning 6-months, curve progression rates for patients weaned at SS7a versus SS7b were 11.4% and 0% respectively for <40° curves. Similarly, curve progression rate for weaning at U7 was 13.5% vs 0% for weaning at U8. Skeletal maturity assessment at weaning using SS6, SS7a/b, SS8 strongly associated (Cramer’s V: .326, P = .016) with whether curve progressed at post-weaning 6 months. Weaning with SS7 subclassification allowed a significant 10.6% reduction of error in predicting curve progression. For curves ≥40°, post-weaning curve progression rate was not associated with any maturity grading at weaning. Conclusion: The use of SS7a and SS7b allows accurate maturity assessment for guiding brace weaning in patients with AIS. Weaning at SS7b or U8 is more appropriate without any curve progression cases immediately post-weaning for small curves <40°. This makes reaching full fusion of both distal radius and ulna physis (SS8) not necessary and brace weaning can be initiated approximately 9.0 months earlier. This study demonstrates the importance of accurate bone age assessment for more precise timing for weaning, avoiding the overuse of bracing while limiting the risk of curve progression. For large curves, curve progression can occur regardless of the skeletal maturity status at which weaning takes place.