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 with 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. Material and Methods A total of 128 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 interrater agreement. Spinopelvic parameters were measured in all the radiographs. The 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. Interrater 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 versus all other patients, TK-PI mismatch for thoracic kyphosis versus all other patients, T11-L2 kyphosis for thoracolumbar kyphosis versus all other patients, global alignment (LL? TK-PI) and SVA for lumbar kyphosis versus global kyphosis, and pelvic tilt for pelvic kyphosis versus 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.

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

“…The compensatory mechanisms that present at the thoracic and lumbar spine, the pelvis and lower limbs have been described [5][6][7]9], and their variations after surgical correction of sagittal malalignment and the correlation of these variations with clinical improvement have been studied. In fact, the presence of compensatory mechanisms is one of the main criteria in a recently described comprehensive classification of sagittal imbalance [9].…”

“…In fact, the presence of compensatory mechanisms is one of the main criteria in a recently described comprehensive classification of sagittal imbalance [9]. The variation of cervical alignment after surgery for sagittal imbalance has received less attention in the scientific literature.…”

“…The inclusion criteria were the following: adult patients, with sagittal imbalance (defined as a SVA [ 50 mm) or hidden imbalance (defined as SVA \ 50 mm in a patient with increased pelvic tilt or knee flexion and lumbar hypolordosis or thoracic hyperkyphosis) [9], treated with a PSO at the thoracic or lumbar spine. Patients with a history of tumor, infection or with incomplete data were excluded from the study.…”

“…These variations in the alignment of the different regions responding to a localized kyphosis or loss of lordosis have been described in the thoracic and lumbar spine and in the pelvis, but also in the cervical spine and the knee joints. As summarized in a recent classification of sagittal deformities by Lamartina and Berjano [9], a thoracic hypokyphosis or lordosis represents the compensation to a lumbar kyphosis, while pelvic retroversion and knee flexion occur as an extreme attempt to restore a sufficient sagittal alignment when kyphosing deformities are present. Lumbar hyperlordosis is a mechanism to keep a normal C7 plumbline when hyperkyphosis is present in the thoracic area or, more frequently at the thoracolumbar junction.…”

Sagittal balance of the spine in patients with osteoporotic vertebral fractures

“…Thus, these postural adjustment strategies affect the environment of the spine and all of them should be assessed to get a comprehensive evaluation of biomechanical conditions of the spine. This has been shown in studies in children and adults with scoliosis, and adults with spinal deformities, and degenerative spondylolisthesis [20][21][22]. There are few studies conducted in postmenopausal women dedicated to the influence of vertebral fractures on global sagittal balance of the spine.…”