Thoracolumbar Scoliosis (AIS) Posterior Surgery Complication

The distal adding-on phenomenon is a known complication after surgical treatment of adolescent idiopathic scoliosis (AIS) that can lead to loss of deformity correction, worsening pain, wedging, and degeneration of the adjacent intervertebral disc, as well as the need for revision surgery. Various factors have been associated with the adding-on phenomenon including age, skeletal maturity, direction of the L4 disc tilt, postoperative shoulder imbalance, and, perhaps most importantly, the selection of the lowest instrumented vertebra (LIV). This chapter provides a case illustration of the adding-on phenomenon along with discussion of various risk factors and a review of pertinent literature. Spinal deformity surgeons must recognize these risk factors for adding-on and choose the LIV carefully to optimize clinical outcomes and avoid the need for revision surgery.