Sensitivity and Specificity of Elliptical Modeling and Sagittal Lumbar Alignment Variables in Normal vs. Acute Low Back Pain Patients: Does Pelvic Morphology Explain Group Lordotic Differences?

Background/Objectives: The lumbar lordosis (LL) is influenced by pelvic morphology, the unique dimensional characteristics of the pelvis. We investigated the sensitivity and specificity of lumbar sagittal radiographic alignment variables to discriminate between normal controls and acute low back pain (ALBP) patients. Methods: A total of 50 normal controls (29 men; mean age of 27.7 ± 8.5 years) with no history of low back pain and 50 ALBP patients (29 men; 28.1 ± 8 years of age) were compared. Radiographic variables included three measures of LL, a b/a elliptical modeling ratio, sacral base angle (SBA), S1 posterior tangent to vertical (PTS1), two measures of pelvic morphology, as well as three relationships between morphology and LL. Descriptive statistics, linear correlations, and receiver operating characteristic (ROC) curves were calculated. Results: The SBA and Cobb T12-S1 LL were significantly greater in the ALBP group. The SBA showed a reasonable ability to discriminate between the normal and ALBP groups with ROC curve analysis (AUC = 0.67, optimal cut-off value = 41.2°, sensitivity = 0.70, and specificity = 0.62). Pelvic morphology was similar between sex and pain groups. Conclusions: Our sample of ALBP patients had similar pelvic morphology as compared to normal control participants; however, they also demonstrated an increased T12-S1 lordosis and sacral base angle, shown as a hyperlordosis.