COPYRIGHT © 2005 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Radiographic Analysis of the Sagittal Alignment and Balance of the Spine in Asymptomatic Subjects

Background: There is an increasing recognition of the clinical importance of the sagittal plane alignment of the spine. A prospective study of several radiographic parameters of the sagittal profile of the spine was conducted to de-termine the physiological values of these parameters, to calculate the variations of these parameters according to epidemiological and morphological data, and to study the relationships among all of these parameters. Methods: Sagittal radiographs of the head, spine, and pelvis of 300 asymptomatic volunteers, made with the sub-ject standing, were evaluated. The following parameters were measured: lumbar lordosis, thoracic kyphosis, T9 sagit-tal offset, sacral slope, pelvic incidence, pelvic tilt, intervertebral angulation, and vertebral wedging angle from T9 to S1. The radiographs were digitized, and all measurements were performed with use of a software program. Two differ-ent analyses, a descriptive analysis characterizing these parameters and a multivariate analysis, were performed in order to study the relationships among all of them. Results: The mean values (and standard deviations) were 60 ° ± 10 ° for maximum lumbar lordosis, 41 ° ± 8.4 ° for sacral slope, 13 ° ± 6 ° for pelvic tilt, 55 ° ± 10.6 ° for pelvic incidence, and 10.3 ° ± 3.1 ° for T9 sagittal offset. A strong correlation was found between the sacral slope and the pelvic incidence (r = 0.8); between maximum lumbar lordosis and sacral slope (r = 0.86); between pelvic incidence and pelvic tilt (r = 0.66); between maximum lumbar lordosis and pelvic incidence, pelvic tilt, and maximum thoracic kyphosis (r = 0.9); and, finally, between pelvic incidence an