Radiographic Features of the Lenke 1A Curves to Help to Determine the Optimum Distal Fusion Level Selection

Abstract

Retrospective study. Investigate the radiographic features of the subtypes of Lenke 1A curves to help to determine the optimum distal fusion level selection. The Lenke 1A was the most frequently evaluated curve type in adolescent idiopathic curves. Miyanji et al suggested that the lumbar modifier type A does not accurately define the behavior of the compensatory lumbar curve in Lenke 1A. The tilt of L3 and L4 in the coronal plane may have a significant role in determining distal fusion level. Thirty-six patients with Lenke type 1A idiopathic scoliosis treated by segmental posterior instrumentation with an average of 52.1-month follow-up were retrospectively analyzed. Four different curve types depending on L3-L4 vertebral tilt were described. The radiographic measurements including proximal and distal junctional kyphosis was obtained at latest follow-up. RESULTS.: Preoperative mean major curve Cobb angle of 47.6° was corrected to 12.9° showing a correction rate of 72.8% and maintained at 14.2°. Loss of correction at final follow-up was 2.7%. The mean compensatory curve Cobb angle of 24.4° was corrected to 8.2°. All patients balanced after surgery although seven had more than -5° clavicle angle before surgery. The mean preoperative and postoperative sagittal T5-T12 angles were 30.6° and 26.2°, respectively, and 29.1° at latest follow-up. The mean preoperative, postoperative, and latest follow-up T10-L2 sagittal Cobb angles were -0.2°, 2.0°, and 4.2°. Three patients diagnosed as distal junctional kyphosis at latest follow-up. Distal fusion level should be extended to at least lower end vertebra (LEV) -1 in type 1A-A and type 1A-D curves, while it might be necessary to go down to LEV in the type 1A-B and 1A-C. It seems that LEV might be a reliable guide to select ideal distal fusion level in Lenke type 1A curves.