Study design: A global and segmental study on standing lateral radiographs of 100 volunteers and 100 patients who had low back pain was undertaken to further define sagittal plane alignment and balance. The volunteer control group and the patient group were matched for age, sex, and size.
Methods: Measurements and determinations made on the standing radiographs included the following: segmental and total lordosis L1-S1 (Cobb method); thoracic kyphosis; thoracic apex; plumbline dropped from the center of C7; and sacral inclination measured between the plumbline and a line drawn along the back of the proximal sacrum.
Results: Segmental lordoses were significantly different between each motion segment in both groups. Approximately two-thirds of total lordosis occurred at the bottom two discs, i.e., L4-5 and L5-S1. Total lordosis was significantly less in the patients and was not age- or sex-related in either group. Patients tended to stand with less distal segmental lordosis, but more proximal lumbar lordosis, a more vertical sacrum and, therefore, more hip extension. This may be related to compensation as C7 sagittal plumb lines were comparable in both groups. Both groups had similar thoracic kyphosis. A much higher percentage of smokers was found in the low back pain patient population studied. Because of the significant amount of angulation in the lower lumbar spine, measurement of lordosis should include the L5-S1 motion segment and be done standing to better assess balance. Sacral inclination is a determinate of both standing pelvic rotation and hip extension. It is strongly correlated with segmental and total lordosis in both volunteers and patients.
Conclusions: Definitions of sagittal balance are provided as well as additional sagittal plane data by which to compare corrections and fusions for different spinal disorders.