期刊正文

The spine literature has been inundated with a myriad of alphabet soup acronyms in an attempt to better evaluate and treat spinal deformity. In many ways, this is a very positive step as surgeons have become increasingly aware of the three-dimensional nature of spinal deformity and that the coronal Cobb angle is only part of the puzzle. The literature on adolescent idiopathic scoliosis has produced no less than seven different measurements to evaluate shoulder balance, none of which has been universally agreed upon. This leaves clinicians wondering how many measurements are really necessary to evaluate radiographic outcomes. However, adult spinal deformity certainly differs from adolescent idiopathic scoliosis. Adult spinal deformity surgery is typically less about fine-tuning appearance and more often focuses on reducing pain and disability. The adult spinal deformity research forum has more recently focused its efforts primarily on the sagittal plane and spinopelvic parameters after the publication of a landmark study by Glassman et al. that centered on the direct impact of global sagittal imbalance on health-related quality-of-life measures. This harkens back to the term “pelvic vertebra” that Jean Dubousset has used for many years to highlight the major influence of pelvic morphology, obliquity, and version in spinal deformity.

Schwab et al. validated the sagittal and spinopelvic parameters of sagittal vertical axis of >40 mm, pelvic tilt of >20°, and a pelvic incidence minus lumbar lordosis mismatch of >10° as primary influences of lower health-related quality-of-life measures and increased Oswestry Disability Index scores in adult spinal deformity. This has been a large step forward as a means of assessing radiographic parameters that can potentially predict disability and assist the surgeon with proper patient selection and goals for surgery.

Smith et al. demonstrated that surgical correction of the above sagittal modifiers led to significant improvements in the minimum clinically important difference threshold in all health-related quality-of-life measures evaluated. No significant improvements were seen in the nonoperative group of the study. Rose et al. incorporated thoracic kyphosis (TK) and pelvic incidence (PI) to predict the lumbar lordosis (LL) necessary to achieve ideal sagittal balance after pedicle subtraction osteotomy with 91% sensitivity using the formula: LL ≤ 45° – TK – PI. Schwab et al. reported that a significant pelvic incidence minus lumbar lordosis mismatch was the strongest direct correlation with disability and poor health-related quality-of-life measures. Sagittal vertical axis and pelvic tilt are not intrinsic components of adult spinal deformity but, rather, are consequences of the deformity as the patient can compensate for sagittal imbalance with pelvic retroversion (improving pelvic tilt) and knee flexion (improving the sagittal vertical axis), while pelvic incidence is a fixed measurement. This supported the theory that correction of pelvic incidence minus lumbar lordosis should be the primary objective in surgical management of adult spinal deformity as it can lead to the concurrent improvement in sagittal vertical axis and pelvic tilt.