Lowest Instrumented Vertebra Selection in AIS

Appropriate selection of the lowest instrumented vertebra (LIV) is crucial to ensure positive outcomes after surgical management of patients with adolescent idiopathic scoliosis. Failure to do so can lead to curve decompensation and "adding on" of additional vertebrae to the deformity. Correct identification of the stable, end, and neutral vertebra, whether the curve(s) is structural or nonstructural, and classifying the type of curve are essential aspects of preoperative planning. Evaluating curve flexibility using fulcrum, side bending, push-prone, and traction can be used to predict the amount of observed postoperative correction for both fused and unfused curves. In addition, these measures can be used to foresee potential residual LIV-tilt and disc wedging postoperatively. Intraoperative techniques such as fine tuning, derotation, wide release, and in situ contouring and instrumentation type used all influence the LIV selection and therefore, must be taken into account preoperatively. Surgical goals when treating adolescent idiopathic scoliosis include achieving a well-balanced spine in all planes while working to preserve segments and therefore, maintain mobility.