Sagittal balance of the pelvis-spine complex and lumbar degenerative diseases. A comparative study about 85 cases

Retrospective analysis of the spino-pelvic alignment in a population of 85 patients with a lumbar degenerative disease. Several previous publications reported the analysis of spino-pelvic alignment in the normal and low back pain population. Data suggested that patients with lumbar diseases have variations of sagittal alignment such as less distal lordosis, more proximal lumbar lordosis and a more vertical sacrum. Nevertheless most of these variations have been reported without reference to the pelvis shape which is well-known to strongly influence spino-pelvic alignment. The objective of this study was to analyse spino-pelvic parameters, including pelvis shape, in a population of 85 patients with a lumbar degenerative disease and compare these patients with a control group of normal volunteers. We analysed three different lumbar degenerative diseases: disc herniation (DH), n = 25; degenerative disc disease (DDD), n = 32; degenerative spondylolisthesis (DSPL), n = 28. Spino-pelvic alignment was analysed pre-operatively on full spine radiographs. Spino-pelvic parameters were measured as following: pelvic incidence, sacral slope, pelvic tilt, lumbar lordosis, thoracic kyphosis, spino-sacral angle and positioning of C7 plumb line. For each group of patients the sagittal profile was compared with a control population of 154 asymptomatic adults that was the subject of a previous study. In order to understand variations of spino-pelvic parameters in the patients’ population a stratification (matching) according to the pelvic incidence was done between the control group and each group of patients. Concerning first the pelvis shape, patients with DH and those with DDD demonstrated to have a mean pelvic incidence equal to 49.8° and 51.6°, respectively, versus 52° for the control group (no significant difference). Only young patients, less than 45 years old, with a disc disease (DH or DDD) demonstrated to have a pelvic incidence significantly lower (48.3°) than the control group, P < 0.05. On the contrary, in the DSPL group the pelvic incidence was significantly greater (60°) than the control group (52°), P < 0.0005. Secondly the three groups of patients were characterized by significant variations in spino-pelvic alignment: anterior translation of the C7 plumb line (P < 0.005 for DH, P < 0.05 for DDD and P < 0.05 for DSPL); loss of lumbar lordosis after matching according to pelvic incidence (P < 0.0005 for DH, DDD and DSPL); decrease of sacral slope after matching according to pelvic incidence (P = 0.001 for DH, P < 0.0005 for DDD and P < 0.0005 for DSPL). Measurement of the pelvic incidence and matching according to this parameter between each group of patients and the control group permitted to understand variations of spino-pelvic parameters in a population of patients.