Current concepts in level selection for fusion in the adolescent idiopathic scoliosis patient

Abstract

Over the past several decades, level selection for fusion in the patient with adolescent idiopathic scoliosis (AIS) has evolved alongside technique. Now, with the near ubiquitous use of pedicle screw fixation, selection criteria have changed to minimize the number of levels fused, especially distally in the lumbar spine. With each additional motion segment preserved, it has been suggested that postoperative function can be improved and the risk of degenerative disease down the line may be decreased. Currently, the Lenke classification for AIS is the most widely used system to describe AIS pathology. Understanding where the structural and nonstructural curves are may help determine the extent of fusion required distally. Proximally, shoulder balance is still considered a key consideration for upper instrumented vertebra (UIV) selection. In terms of the lowest instrumented vertebra (LIV), we focus on two key concepts to prevent serious complications such as distal junctional kyphosis (DJK) or adding-on phenomenon: the last touched vertebra (LTV) and the stable sagittal vertebra. In the AP radiograph, identifying the LTV as the LIV may allow the surgeon to save a fusion level without increasing risk of DJK or adding-on. However, one must also consider the sagittal plane; the authors identify the stable sagittal vertebra on the lateral radiograph to help determine the optimal LIV; of these two criteria, the more distal level will be selected to decrease the chance of adverse outcomes.