Spinopelvic alignment of patients with degenerative spondylolisthesis.

OBJECTIVE: The main objectives of this study were to analyze and compare spinopelvic parameters, including the pelvis shape, in a population of 40 patients with degenerative spondylolisthesis (DSPL) and to compare these patients with a control group of asymptomatic volunteers.

METHODS: Forty patients with DSPL were included in this study. Spinopelvic parameters were analyzed on preoperative full spine x-rays in a standardized standing position. The following spinopelvic parameters were measured: pelvic incidence (PI), sacral slope, pelvic tilt, lumbar lordosis, thoracic kyphosis, and positioning of the C7 plumb line. The population of patients was compared with a control population of 154 normal and asymptomatic adults who were studied in a recently published study. In order to understand variations of spinopelvic parameters, a control group was matched according to the PI, which is a morphological parameter.

RESULTS: The PI was significantly greater for patients with DSPL (60.1 +/- 10.6 degrees) compared with the control group (52 +/- 10.7 degrees) (P < 0.0005). After matching according to the pelvic incidence, the DSPL population was characterized by an anterior translation of the C7 plumb line (P < 0.05), a loss of lumbar lordosis (P < 0.0005), and a decrease of the sacral slope (P < 0.0005). Retrolisthesis and/or segmental intervertebral hyperextension were observed in the upper lumbar spine in 30% of the cases.

CONCLUSION: Matching according to the PI between the patients in the study and the control group enabled us to understand variations of the spinopelvic parameters in a population of patients with DSPL. DSPL patients were characterized by a greater PI than the asymptomatic population; therefore, we suggest that a high PI may be a predisposing factor in developing DSPL. Finally, we observed significant variations in spinopelvic alignment, such as loss of lordosis and sagittal unbalance, which were partially compensated by pelvis back tilt and hyperextension in the upper lumbar spine.