Modern Concepts in Sagittal Curve Measurement: Comparison of Spline-based and Fixed Landmark Measurements in a Cohort of 1520 Healthy Subjects.

STUDY DESIGN:Retrospective multicenter study. OBJECTIVE:Our objective was to compare the spline-based measurement of sagittal spinal curvatures to fixed landmarks in a normative population. SUMMARY OF BACKGROUND DATA:Recent research has stressed the importance of considering sagittal curvature in their entirety using a spline reconstruction. To date, no data supports the superiority of this method in comparison to classic measurement methods. METHODS:Full spine biplanar radiographs of subjects over 20 years old who had normal radiographs were analyzed. Thoracic kyphosis (TK) and lumbar lordosis (LL) were measured following 2 modalities: either using predefined landmarks (TKT1T12, TKT5T12 and LLL1S1) or spline-based measurement (TKSpline and LLspline). RESULTS:1520 subjects were included (mean 54yo). The mean difference between TKspline and TKT1T12 was 1.4° and between TKspline and TKT5T12 was 11.7° (P<0.001). LLslpine was significantly larger than LLL1S1 (55° vs 54°, P<0.001). LLslpine and LLL1S1 were correlated (R=0.950, P<0.001). Pelvic incidence had no influence on the difference between LLslpine and LLL1S1 (R=-0.034, P=0.184). Using LLL1S1 measurements, LL was underestimated in 17% of the cases. The comparison of outlier distribution according to age groups (P=0.175), gender (P=0.937) or PI groups (P=0.662) found no difference. There were significantly more outliers in Roussouly type 1 compared to other types (56%, P<0.001). CONCLUSION:Our results suggest that the use of TKT1T12 and LLL1S1 is acceptable to assess spinal sagittal curvatures. However, TKT5T12 is not accurate for thoracic curve and should be used with caution. LLL1S1 can be used to accurately assess the lumbar curve, except in Roussouly type 1.