Postoperative Shoulder Imbalance (psi) and Adding-On Phenomenon

Abstract

Scoliosis is a three-dimensional spinal deformity involving axial-plane rotation, lateral curvature in the coronal plane, and alteration of the sagittal spinal profile. Surgical treatment is still considered the definitive treatment option for patients with severe scoliosis. Spine surgeons universally aim to fuse the smallest number of motion segments necessary to create a satisfactory balance of the trunk, shoulders, neck and pelvis. Several conditions militate in favor of fusing more segments, rather than fewer: we address two of them: post-operative shoulder imbalance (PSI), and the adding-on phenomenon (AO). The definition of PSI remains controversial. Cosmetic shoulder balance is a major concern for patients with scoliosis, although surgeons are commonly more concerned with radiological shoulder balance. No consensus exists on the incidence of, or risk factors for, PSI. Additional research is needed to reveal PSI risk factors and quantify its incidence. Although the clinical implications of AO remain unclear, decompensation of coronal balance can lead to unfavorable radiological and clinical outcomes, which may require revision surgery. Extension of the primary curve, disc wedging, and degenerative changes may necessitate extending the fusion distally. The radiological and clinical parameters mentioned throughout this chapter will help deformity surgeons to identify the onset of AO. Meticulous preoperative planning and adequate surgical technique is mandatory to achieve a balanced spine and prevent AO in high-risk patients with adolescent idiopathic scoliosis. If it occurs regardless, there are still treatment options available, and we will review some of these here. © 2018 Nova Science Publishers, Inc. All rights reserved.