Predicting ideal spinopelvic balance in adult spinal deformity

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Spinopelvic balance is based on the theory that adjacent segments of the spine are related and influenced by one another. By understanding the correlation between the thoracolumbar spine and the pelvis, a concept of spinopelvic balance can be applied to adult deformity. The purpose of this study was to develop a mathematical relationship between the pelvis and spine and apply it to a population of adults who had undergone spinal deformity surgery to determine whether patients in spinopelvic balance have improved health measures.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Using values published in the literature, a mathematical relationship between the spine and pelvis was derived where pelvic incidence (PI) was divided by the sum of the lumbosacral lordosis (LL; T12–S1) plus the main thoracic kyphosis (TK; T4–12). The result was termed the spinopelvic constant (r): r = PI/(LL + TK). This was performed in patients in 2 age groups previously defined in the literature as “adult” (18–60 years of age) and “geriatric” (&gt; 60 years). The equation was then constructed to relate an individual's measured PI to his or her predicted thoracolumbar curvature (LL + TK)<jats:sub>p</jats:sub> based on the age-specific spinopelvic constant: (LL + TK)<jats:sub>p</jats:sub> = r/PI. A retrospective review was then performed using cases involving patients who had undergone spine deformity surgery and were enrolled in our spinal deformity database. Sagittal balance, PI, and the sum of the main thoracic and lumbar curves were measured. The difference between the predicted sum of the regional curves (LL + TK)<jats:sub>p</jats:sub>, based on the individual's measured PI and the age-specific spinopelvic constant, and the measured sum of the regional curves (LL + TK)<jats:sub>m</jats:sub> was then calculated to determine the degree of spinopelvic imbalance. Health status measures were then compared.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Using the formula r = PI/(TK = LL) and normative values in the literature, the adult spinopelvic constant was calculated to be −2.57, and the geriatric constant −5.45. For the second portion of the study, 41 patients met inclusion criteria (13 classified as nongeriatric adults and 28 as geriatric patients). Application of these constants found a statistically significant decline in almost all outcome categories when the spinopelvic balance showed at least 10° of kyphosis more than predicted. While not statistically significant, the trend was that better outcomes were associated with a spinopelvic balance within 0 to +10° of the predicted value. The final analysis compared and separated outcomes from sagittal balance and spinopelvic balance. For patients to be considered in sagittal balance, they must be within 50 mm (± 50 mm) of neutral. For patients to be considered in spinopelvic balance, they must be within ± 10° of predicted spinopelvic balance. Patients in both sagittal and spinopelvic balance have statistically significant better outcomes than those in neither sagittal nor spinopelvic balance. Except for the mean SF-12 PCS (12-Item Short-Form Health Survey Physical Component Summary), there were no significant differences between those that were either in sagittal or spinopelvic balance, but not the other.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Restoring a normative relationship between the spine and the pelvis during adult deformity correction may play an important role in determining surgical outcomes in these patients independent of sagittal balance.</jats:p></jats:sec>

Classification of sagittal imbalance based on spinal alignment and compensatory mechanisms

“…Previous papers have identified formulae that allow calculation of ideal lumbar lordosis and pelvic tilt from pelvic incidence [9,14]. Other provides data to calculate ideal thoracic kyphosis [15].…”

“…The following spinopelvic parameters were measured from the radiographs: pelvic incidence (PI), pelvic tilt (PT), lumbar lordosis (LL), L4-S1 lordosis (L L4-S1 ), thoracolumbar lordosis (L T11-L2 ), thoracic kyphosis, C7-S1 sagittal vertical axis (SVA) and C2-C7 sagittal vertical axis (C2-C7 SVA). Previously published formulae and data were used to estimate the ideal sagittal parameters based on pelvic incidence [9,14,15]. Two senior spinal surgeons evaluated all the films and after discussion defined eight deformity patterns (including normal sagittal alignment).…”

Criteria to restore the sagittal balance in deformity and degenerative spondylolisthesis

“…Recently, Neal et al [17] have suggested a new parameter to evaluate spinopelvic balance. They calculated from normative values in literature a spinopelvic constant, which is the quotient between pelvic incidence and the number of degrees that lumbar lordosis exceeds thoracic kyphosis.…”

Variations of cervical lordosis and head alignment after pedicle subtraction osteotomy surgery for sagittal imbalance

“…The correlation between the thoracic and lumbar spine and pelvic parameters is well known [2][3][4], and the rules that describe these connections are used by spinal surgeons to adequately plan surgery [8].…”

“…Different mathematical rules have been proposed to describe the correlation between pelvic and spinal parameters in asymptomatic and sagittally balanced patients. Their application to subjects with spinal deformity has shown how a correct harmony between the shape of the thoracolumbar spine and the pelvis is a crucial factor in maintaining a correct balance without increased muscle effort and consequently without increased pain and disability [2][3][4]. At the same time compensatory mechanisms that attempt to restore a vertical trunk alignment in patients with sagittal deformity, have been observed and described [5][6][7][8].…”