Criteria to restore the sagittal balance in deformity and degenerative spondylolisthesis

Abstract

Purpose To present in a single source the relevant information needed to assess spinopelvic balance and alignment, and to estimate the amount of correction needed in a patient during surgical treatment. Methods Narrative literature review Results Sagittal balance can be evaluated by global balance estimates (sagittal vertical axis and T1 tilt). Other important parameters are the relationship between pelvic incidence and lumbar lordosis (spinopelvic harmony), between pelvic incidence and difference of thoracic kyphosis and lumbar lordosis (spinopelvic balance), excess of pelvic tilt, knee flexion and thoracic compensatory hypokyphosis. Different methods to calculate the amount of surgical correction needed in patients with sagittal imbalance have been based on combinations of these parameters. Conclusions Relevant parameters of sagittal imbalance have been identified and correlated with clinical outcomes. Methods for calculation of surgical correction of imbalance have been proposed, but not validated in patients with midterm follow-up.

Classification of sagittal imbalance based on spinal alignment and compensatory mechanisms

“…By definition, this produces an imbalanced spine (the subject is not able to keep upright position with low muscle activity). This situation has been defined as compensated imbalance [1] or compensating imbalance [25]. We believe that the Fig.…”

“…Sagittal balance reflects a shape of the spine that allows it to keep the standing position with little muscle effort [1]. The shape of the spine is the result of the sum of the shapes of bony elements (the vertebrae) and discs.…”

“…Much of the research effort in this field has focused on calculation of the amount of correction needed in degenerative or postsurgical sagittal imbalance [1,[8][9][10] and identification of ideal fusion levels in thoracic kyphosis (TK) [11]. Some problems remain unsolved, such as the ideal proximal level to fuse in degenerative or postsurgical imbalance, or identification of patients at risk of proximal junctional kyphosis [12].…”

Compensatory mechanisms contributing to keep the sagittal balance of the spine

“…Recent studies support the idea that analysis of sagittal balance is a crucial keypoint to optimize the management of lumbar degenerative diseases, especially when spinal instrumentation is intended [7,13,15,16].…”

“…The compensatory mechanisms contribute to keep the sagittal balance of the spine above the pelvis, thus limiting the consequences of lumbar kyphosis in terms of sagittal anterior imbalance. They are observed in the spine, pelvis and/or lower limb areas and can be associated [15].…”