The Importance of Apex Location and Proximal Hemi-Curve Morphology for the Surgical Tactic of Significant Convex Coronal Imbalance in Patients with Dystrophic Scoliosis Secondary to Type I Neurofibromatosis: Classification and Management

Abstract Background. There was a paucity of valid information on how to discriminate between different patterns of convex coronal imbalance (CCI>3cm) in dystrophic scoliosis secondary to Type I neurofibromatosis (DS-NF1), while aggravated postoperative CCI occurred regularly with the causes being insufficiently investigated. We aimed to develop a new classification of CCI in DS-NF1, and to optimize the coronal rebalancing strategies.Methods. NF1-related scoliosis database was reviewed and different types of CCI were identified, and the outcomes of coronal rebalance were analyzed. Results. Two main CCI patterns were defined: thoracic CCI (Type 1) and thoracolumbar/lumbar CCI (Type 2), and were further subtyped by the compensatory behavior of the upper hemi-curve (straight or curved morphology). The incidence of immediate post-op CCI was 0.0% and 63.6% for Type1 and Type 2 groups, respectively. Mismatch of both translation and inclination correction between the upper and lower hemi-curve was significant in the post-op coronal imbalanced group (△Upper Arc Translation/△Lower Arc Translation: 109.6±60.0% vs. 31.8±34.4%, p=0.008; △Upper Arc Inclination/△Lower Arc Inclination: 89.8±36.6% vs. 33.5±37.3%, p=0.012). Multiple linear regression analysis revealed that △UAT/△LAT significantly correlated with the correction of coronal balance distance (β=-21.567; p=0.018). A surgical rebalancing algorithm was proposed to treat each subtype.Conclusion. Thoracolumbar/lumbar CCI in dystrophic scoliosis was prone to suffer high risk of persistent post-op CCI. Satisfying coronal rebalance should rely on maximal translational correction of lower hemi-curve, while the upper hemi-curve played the role of fine-tuning for coronal realignment rather than radical Cobb correction, straight morphology in particular.