Normative spino-pelvic parameters in patients with the lumbarization of S1 compared to a normal asymptomatic population.

INTRODUCTION: Normal spino-pelvic values for patients with lumbarization of S1 have not been described in the literature. Presented are the normal values for this population group, the prevalence of S1 lumbarization, and the correlation between pelvic incidence (PI) and lumbar lordosis (LL) in this group.

METHODS: Two databases of asymptomatic patients were combined to identify 11 patients with the lumbarization of S1. The whole spine images were used to measure the true prevalence rate. Lumbar 3D EOS models were built to measure spino-pelvic parameters for the lumbarization group compared to the asymptomatic population. Seven patients appeared at first to have six lumbar vertebrae, but counting caudally from C2 showed this was not the case.

RESULTS: 11/268 patients demonstrated the lumbarization of S1 to give a true prevalence rate of 4.1 %. The lumbarization group demonstrated a statistically significant difference with regard to PI, PT, and SS, and total lordosis measured from superior endplate of L1 to the superior endplate of the first fixed sacral segment. L6I was not significantly correlated to lordosis; however, PI did have a significant correlation with lordosis. Lordosis could be estimated in this group by the equation: [Formula: see text].

CONCLUSION: Incomplete imaging of the spine may lead to false estimation of the prevalence of lumbarization. Patients with lumbarization have higher lordosis values and lordosis can now be estimated during pre-operative planning for this group.