Increased Pelvic Incidence is Associated With a More Coronal Facet Orientation in the Lower Lumbar Spine: A Cadaveric Study of 599 Lumbar Spines.

STUDY DESIGN An anatomic study of facet angle orientation and morphology of the lumbar spine was performed. OBJECTIVE The aim of this study was to determine how age, gender, race, and pelvic incidence (PI) correlate with facet orientation in the lumbar spine. SUMMARY OF BACKGROUND DATA Lumbar facet orientation has important implications in the development of numerous pathologies of the spine, including arthritis, spondylolisthesis, and adult spinal deformity. Preliminary reports have suggested that sagittal balance of the spine may contribute to facet joint orientation. We therefore designed an anatomic study to investigate the relationship between PI and facet orientation, within the context of age, gender, and race. METHODS Five hundred ninety-nine cadaveric lumbar spines were obtained from the Hamann-Todd osteological collection. It was determined that facet angle was most reliably assessed by measuring the angle between the superior articular facet and the spinous process. Facet angles were measured bilaterally at each level from T12-L1 through L5-S1 in every specimen. Multivariate regression analysis was used to determine independent predictors of facet angle at each level. RESULTS Facet angle increased rostrally to caudally, from 22.6 ± 8.3° at T12-L1 to 49.1 ± 12.4° at L5-S1. Cadaver age was an independent predictor of a more sagittal facet angle at lower spinal levels. Caucasian race was an independent predictor of increasing facet angle. Increased PI had no effect on facet angle at T12-L1, L1-L2, L2-L3, or L3-L4, although was a significant predictor of more coronally oriented facet joints at L4-L5 (standardized beta 0.096, P = 0.009) and L5-S1 (standardized beta 0.079, P = 0.032). CONCLUSION The results of this study provide important data regarding differences in facet angle that exists between individuals. Moreover, the results of this study suggest that facet joints do possess the ability to remodel over time, perhaps in response to perturbations of sagittal balance, osteophyte formation, or other yet to be determined factors. LEVEL OF EVIDENCE N/A.