Does Sacral Slanting Affect Distal Adding-on in Lenke Type 1A Adolescent Idiopathic Scoliosis?

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Study Design.A retrospective clinical study.Objective.The purpose of this study was to identify risk factors for postoperative distal adding-on in Lenke 1A adolescent idiopathic scoliosis.Summary of Background Data.Distal adding-on is a postoperative complication associated with the Lenke type 1A curve. Although various factors are known to cause postoperative adding-on, no study has reported a correlation between sacral slanting and adding-on.Methods.A total of 126 consecutive patients who underwent posterior correction and fusion surgery for Lenke type 1A adolescent idiopathic scoliosis were included in this study. Curve type was further categorized into L4-left (L4-L) or L4-right (L4-R), based on the direction of the L4 vertebral tilt. Several clinical and radiological parameters including sacral slanting were investigated to identify risk factors associated with postoperative distal adding-on.Results.A total of 36 patients (28.6%) exhibited sacral slanting. Nineteen out of 20 L4-L type patients had left-sided sacral slanting, whereas 12 out of 16 L4-R type patients had right-sided sacral slanting. The group with adding-on (n = 13) demonstrated a significantly lower age than the group without adding-on (n = 113). Preoperative lumbar Cobb angle (P = 0.022) was determined to be an independent factor for adding-on according to logistic regression analysis. In the L4-R type, the last touching vertebra (LTV) level and the gap difference in levels between lowest instrumented vertebra and LTV (lowest instrumented vertebra-LTV) comprised significant variables.Conclusion.Sacral slanting typically occurs to the left in the L4-L type and to the right in the L4-R type. The size of the preoperative lumbar curve was found to be an independent risk factor that caused adding-on in patients with Lenke type 1A scoliosis. In the L4-R type, right-sided sacral slanting tended to lower the LTV. Therefore, the fusion level might be shorter to save the motion segments resulting in distal adding-on.Level of Evidence: 4

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