Axial plane analysis of Lenke 1A adolescent idiopathic scoliosis as an aid to identify curve characteristics.

Background Context: Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional (3D) deformity of the spine involving deviations in the frontal plane, modifications of the sagittal profile, and rotations in the transverse plane. Although Lenke classification system is based on 2D radiographs and includes sagittal thoracic and coronal lumbar modifiers, Lenke et al. suggested inclusion of axial thoracic and lumbar modifiers in the analysis.

Purpose: To analyze axial plane of Lenke 1A curves to identify curve characteristics.

Study Design: Retrospective study.

Patient Sample: Seventy patients (49 women, 21 men) with Lenke Type 1A idiopathic scoliosis were analyzed.

Outcome Measures: Coronal, sagittal, and axial parameters were measured from plain radiographs that were obtained at initial medical examination of the patients.

Methods: Coronal and sagittal plane and whole spine segmental vertebra rotations from thoracic 1 to lumbar 5 were evaluated in 70 AIS patients with Lenke 1A curves by using Drerup method. Three different subgroups were identified according to magnitude and direction of lower end vertebra (LEV) rotation.

Results: In Group 1 (Lenke 1A1), the direction of LEV rotation was same with other vertebrae in the main curve and the magnitude of the LEV rotation was less than -0.5°. In Group 2 (Lenke 1A2), the rotation of LEV was between -0.5° and 0.5° and so was accepted as neutral. In Group 3 (Lenke 1A3), the rotation of LEV had opposite direction with vertebrae in the main curve and the magnitude of LEV rotation was more than 0.5°. The mean thoracic Cobb angle of patients with Lenke 1A idiopathic scoliosis was 51.1° (range 37°-80°), whereas the mean lumbar Cobb angle was 16.4° (range 0°-32°). The mean angle of trunk rotation of the patients was 5.7° (range 1°-16°). In terms of maximum thoracic vertebra rotation, the mean rotation angle of Lenke 1A idiopathic curves was -18.9° (range -(9.8°-44.7°)). The mean maximum lumbar vertebra rotation was 4.5° (range -7.2° to 15.1°).

Conclusions: Addition of axial plane analysis to conventional coronal and sagittal evaluations in patients with Lenke 1A curves may reveal inherent structural differences that are not apparent in single planar radiographic assessments and may necessitate a different surgical strategy.