Are Thoracic Curves With a Low Apex (T11 or T11/T12) Really Thoracic Curves?

Study DesignMulticenter; review of prospectively collected data.ObjectivesTo determine whether curves with an apex at T11 or T11/T12 represent a combination of thoracic and thoracolumbar curves or constitute their own class of curves.Summary of Background DataCurves with an apex at T11 and T11/T12 are classified by the Scoliosis Research Society and Lenke classification as thoracic curves.MethodsWe reviewed 1,835 adolescent idiopathic scoliosis cases from a multicenter database. Based on the most common curve apex levels (thoracic [TH] curves, T9; thoracolumbar/lumbar [TL/L] curves, L1), we created 2 comparison groups that represented classic examples of TH and TL/L curves. We identified 66 cases with an apex at T11–T11/T12 and compared them with 320 cases with a T9 apex, and 126 cases with an L1 apex. We compared characteristics of these 3 groups (p < .05) and completed a radiographic review of the T11–T11/T12 group.ResultsThe curve direction of the 3 groups was significantly different (TL/L, 84% left; TH, 3% left; and T11–T11/T12, 16% left) (p < .001). The mean number of vertebrae in curves for the T11–T11/T12 group (7.1 ± 1.2) fell between the value for the TL/L (5.7 ± 0.8) and TH (7.3 ± 1.0) groups. The T11–T11/T12 curves had a greater trunk shift than TL/L (p = .002) and TH (p = .011) curves. There was no difference among the 3 groups in terms of major curve Cobb magnitude (p = .09) or age at surgery (p = .76). Radiographic review of the T11–T11/T12 curves revealed 3 curve patterns: 21 long single curves (32%), 28 short single curves (42%), and 17 double thoracic curves (26%).ConclusionsWe suggest caution in lumping curves with an apex at T11 or T11–12 disc together with other thoracic apices in studies involving primary thoracic curves, because some of these curves have features much more typical of thoracolumbar curves.