Is the Lumbar Modifier Useful in Surgical Decision Making? Defining Two Distinct Lenke 1A Curve Patterns

Study Design. Retrospective review of adolescent idiopathic scoliosis (AIS) patients. Objective. To investigate the clinical deformity and radiographic features of Lenke 1A and 1B curves to determine if the A and B lumbar modifiers actually describe 2 distinct curve patterns. Summary of Background Data. The Lenke classification system attempts to address some of the shortcomings of the King-Moe classification system by providing a more comprehensive, reliable, and treatment-based categorization of all AIS deformities. Although this classification is useful in determining which regions of the spine should be fused, it does not necessarily divide AIS curves into distinct patterns. Methods. A critical analysis of the clinical deformity, radiographic features, and surgical treatment of AIS patients with Lenke 1A and 1B right thoracic curves was performed. Lenke 1A curves were differentiated according to the L4 coronal plane tilt. Analysis of variance and Pearson chi(2) analysis were used to perform statistical comparisons between the individual curve patterns (P <= 0.05). Results. Ninety-three patients with preoperative and 2-year postoperative data were included in this analysis (65 Lenke 1A, and 28 Lenke 1B). Thirty-three patients were subdivided as 1A-L (L4 tilted to the left) and 32 patients were subdivided as 1A-R (L4 tilted to the right). The inter-observer reliability for determining the direction of L4 tilt was excellent (kappa = 0.94, P <= 0.001). Patients with 1A-L curves were similar to patients with 1B curves with respect to the L4 tilt and the location of the stable vertebra (most often in the thoracolumbar junction). In contrast, patients with 1A-R curves had a more distal stable vertebra (most often L3 or L4). The surgical treatment also differed between these 2 groups with regards to the lowest instrumented vertebra (LIV). 1A-L and 1B curves were similar with a median LIV of T12, whereas the 1A-R curves had a more distal median LIV of L2 (P = 0.01). Conclusion. Two Lenke 1A curve patterns can be described based on the direction of the L4 tilt. This distinction has ramifications regarding selection of fusion levels and assessing surgical outcomes. The A and B lumbar modifiers do not describe 2 distinct curve types within the Lenke 1 group; however, the tilt direction of L4 does allow subdivision of the Lenke 1A curves into 2 distinguishable patterns (1A-R and 1A-L). The 1A-L curves are similar to 1B curves and different in form and treatment from the 1A-R pattern.