Assessment of spino-pelvic morphometry, a predictor of lumbosacral instability

Background: Spino-pelvic malalignment may be responsible for accelerated degeneration of the lumbar spine and consequent instability. Previous studies have documented the high degree of variability in the sagittal alignment of the lumbar spine and specific parameters have been identified.Objectives: To evaluate correlations between sagittal spino-pelvic parameters and development of lumbosacral degeneration and instability.Design: Case-series radiographic study.Methods: In the course of this study, consecutive anteroposterior and lateral radiographs of 197 symptomatic individuals (low back pain) were analyzed between January 2012 and December 2014. One hundred and twenty four plain X-ray films of these patients were selected for the study after undergoing MRI scanning. Parameters measurements on the lateral plain films were lumbar lordosis, sacral slope, pelvic tilt, pelvic incidence and sacral overhang.Results: A total of 124 patients (mean age 43.8 years, SD 13.1) were enrolled. There were 56 males and 68 females. Patients were grouped as having instability (Group1) and those without instability (Group 2). The two groups were compared. Group 1 patients were found to be younger (58 vs. 45 years, P < 0.0543), had greater sacral inclination (41.3° vs. 33.8°, P < 0.0232), and a larger pelvic incidence (66.4° vs. 55.2°, P < 0.00038). The differences in pelvic tilt (24.3° vs. 21.6°, P < 0.4503) and sacral overhang (45.3mm vs. 39.8 mm, P < 0.3670) were not statistically significant. There was an increased pelvic incidence/lumbar lordosis mismatch in group compared to Group 2 (PI-LL; 29 vs. 18; P < 0.0899).Conclusions: Sagittal spinopelvic morphometry, particularly a decreased sacral slope and an increased pelvic incidence are useful guide for identifying instability in patients with chronic low back pain. This will assist in planning operative management