Radiographic features of the Lenke 1A curves to help to determine the optimum distal fusion level selection.

Study Design: Retrospective study.

Objective: Investigate the radiographic features of the subtypes of Lenke 1A curves to help to determine the optimum distal fusion level selection.

Summary Of Background Data: 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.

Methods: 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.

Conclusion: 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.