Objective: In this literature review, the authors analyze data from previously published studies that evaluated neutral upright spinal alignment (NUSA) from the occiput to the pelvis in asymptomatic individuals. Based on the data for NUSA in asymptomatic volunteers, a new classification is proposed for spinal deformity.
Methods: A review of the English literature was conducted to identify studies evaluating NUSA from the occiput to the pelvis in asymptomatic juvenile, adolescent, adult, and geriatric volunteers. From the literature review, 17 angles and displacements were selected to depict neutral upright coronal and axial spinal alignment, and 21 angles and displacements were selected to depict neutral upright sagittal spinal alignment. Pooled estimates of the mean and variance were calculated for the angles and displacements from the articles that met inclusion criteria. A new classification of spinal deformity was then developed based on age-dependent NUSA; spinal abnormality; deformity curve location, pattern, magnitude, and flexibility; and global spinal alignment.
Results: Despite a wide variation in the regional curves from the occiput to the pelvis in asymptomatic volunteers, global spinal alignment is maintained in a narrow range for preservation of horizontal gaze and balance of the spine over the pelvis and femoral heads.
Conclusion: A new classification of spinal deformity is proposed that provides a structure for defining deformity of all patient ages and spinal abnormalities.