Classification of sagittal imbalance based on spinal alignment and compensatory mechanisms

Abstract

Introduction Sagittal balance is an independent predictor of clinical outcomes in spinal care. Surgical treatment is challenging and jeopardized by frequent complications. Guidelines for surgical treatment are currently not based on a classification of the disease. A comprehensive classification of sagittal balance based on regional deformities and compensatory mechanisms combined in deformity patterns is proposed. Though the sagittal shape of the spine can change due to degeneration or trauma, correlations between sagittal shape parameters and pelvic incidence (PI) have been described. Pelvic incidence is not changed by degeneration, thus representing a permanent source of information on the original sagittal shape of the spine. Methods One hundred and twenty-eight full-spine lateral standing radiographs of patients with different spinal conditions were evaluated and classified by one rater. One random subseries of 35 patients was evaluated by two raters for calculation of inter-rater agreement. Spinopelvic parameters were measured in all the radiographs. Internal validity of the classification system was evaluated comparing the values of regional sagittal parameters that distinguish one category from the others. Results Eight different patterns were identified regarding the site of the deformity and the presence of compensatory mechanisms: cervical, thoracic, thoracolumbar junction, lumbar, lower lumbar, global and pelvic kyphosis and normal sagittal alignment. Inter-rater agreement was almost perfect (j = 0.963). Statistically significant differences were found comparing the means of selected sagittal spinopelvic parameters that conceptually divide pairs or groups of categories: C2-C7 SVA for cervical kyphosis vs all other patients, TK-PI mismatch for thoracic kyphosis vs all other patients, T11-L2 kyphosis for thoracolumbar kyphosis vs all other patients, global alignment (LL?TK-PI) and SVA for lumbar kyphosis vs global kyphosis and pelvic tilt for pelvic kyphosis vs lumbar, lower lumbar and global kyphosis. Conclusion A comprehensive classification of sagittal imbalance is presented. This classification permits a better interpretation of the deformity and muscle forces acting on the spine, and helps surgical planning. Preliminary validation has been provided.

Pedicle subtraction osteotomies (PSO) in the lumbar spine for sagittal deformities

“…Recent classifications [4,5] of adult deformity take into account sagittal alignment as a major factor determining outcomes. Recently, a validated, comprehensive classification of sagittal deformities has improved the comprehension of the deformity, showing how sagittal misalignment in any region of the spine has an influence on the rest of the spine, with reciprocal compensatory changes that express as deformity patterns (regional deformity plus typical compensatory changes for each type of deformity are a deformity pattern), and assisting the surgical planning [6].…”

Sagittal Alignment in Spinal Deformity: Implications for the Non-Operative Care Practitioner

“…Compensatory mechanisms are changes in the sagittal alignment of spinal or non-spinal segments, different from those involved in regional deformity, to restore the alignment of the gravity line or the horizontal gaze. Compensatory mechanisms need active muscle contraction by the subject [24,25]. When the SS is high (>45°), a regional hyper-lordosis lumbar deformity along with compensatory thoracic hyper-kyphosis may commonly be observed [23].…”

“…A mean value PI was documented in 2011 to be 55 ± 10° [24], and a mean value of LL and thoracic kyphosis (TK) was documented in 1989 to be 44 and 36° [26]. These mean values do not imply ideal but simply a fixed angle providing anatomical characteristics of the pelvis and lumbar spine.…”

“…The most documented [24][25][26] types of mismatches in adolescent idiopathic scoliosis (AIS) and ASD include those with PI-LL >10° where the PI is high and the LL is low (Figure 9). …”

Osteotomies of the spine: “Technique of the Decade”?

“…Currently, we are able to assess and quantify the degree and type of the deformity based on spino-pelvic parameters with correlations, rules, and classifications [5]. This allows us to direct candidates to a surgical or non-surgical management, to establish a preoperative plan based on precise calculation of surgical goals, and intraoperatively measure the degree to which the objectives are being achieved.…”