Analysis of Concave and Convex Rib-vertebral Angle, Angle Difference, and Angle Ratio in Patients With Lenke Type 1 Main Thoracic Adolescent Idiopathic Scoliosis Treated by Observation, Bracing or Posterior Fusion, and Instrumentation

Abstract

Retrospective review. The aim of this study is to describe the radiologic changes in rib-vertebral angles (RVAs), rib-vertebral angle differences (RVADs), and rib-vertebral angle ratios (RVARas) in patients with Lenke type 1 main thoracic adolescent idiopathic scoliosis treated by observation, bracing, or posterior fusion and instrumentation, and to compare these with normal individuals. The RVA measurement has been shown to be a valid and reproducible method and its asymmetries are related to age, sex, and laterality patterns of the curvature. However, studies of RVA and RVAD in patients with adolescent idiopathic scoliosis are scarce and there are no data regarding the assessment of the ratio between concave and convex RVA. A retrospective chart and radiograph review was carried out for 66 consecutive adolescent female patients with Lenke type 1 main thoracic idiopathic scoliosis and 14 normal counterparts. Patients were divided into 5 groups: normal individuals (group 1); scoliotic patients with Cobb angle <30 degrees (group 2A); scoliotic patients with Cobb angle more than 30 degrees (group 2B), scoliotic patients treated by bracing (group 3), and scoliotic patients treated by posterior fusion and instrumentation (group 4). Overall values (mean ± SD) of the RVAs on the concave side were 90.5 ± 17 degrees in group 1, 90.3 ± 15.8 degrees in group 2A, 88.8 ± 15.4 degrees in group 2B, 87.5 ± 13.3 degrees in group 3, and 86.7 ± 17 degrees in group 4. On the convex side, values were 90.0 ± 17.3 degrees in group 1, 86.3 ± 13.7 degrees in group 2A, 80.7 ± 14.4 degrees in group 2B, 82.9 ± 13.2 degrees in group 3, and 81.7 ± 16.2 degrees in group 4. Overall values (mean ± SD) of the RVADs at all levels were 0.5 ± 0.7 degrees in group 1, 4 ± 4.8 degrees in group 2A, 8 ± 4 degrees in group 2B, 4.7 ± 5.6 degrees in group 3, and 5.1 ± 5.2 degrees in group 4. The RVARa values (mean ± SD) at all levels were 1.008 ± 0.012 degrees in group 1, 1.041 ± 0.061 degrees in group 2A, 1.102 ± 0.151 degrees in group 2B, 1.056 ± 0.078 degrees in group 3, and 1.061 ± 0.071 degrees in group 4. Convex RVA was smaller than concave RVA between T1 and T10 in all groups of patients. RVAD and RVARa values in the scoliotic segment were greater in patients with untreated scoliosis more than 40 degrees than in patients with an untreated deformity of <25 degrees or in patients, treated by bracing or surgery, with a residual curve of <25 degrees. These measurements are a useful tool in the armamentarium of the surgeon treating spinal deformities and could be used to better characterize the deformity and/or to evaluate effects of brace or surgical treatment.