The change in lumbar lordosis from the standing to the lateral position: implications for lateral interbody fusion

Purpose The purpose of this cross-sectional, observational study was to establish the relationship between standing lumbar lordosis (LL) and lateral decubitus LL. Methods Forty-nine subjects, 24 male and 25 female, were prospectively enrolled. Patients with pre-existing spinopelvic pathology were excluded. Standing, relaxed-seated, and lateral decubitus lateral radiographs were obtained. Radiographic variables measured included LL and lordosis change at each lumbar level (e.g. L1-L2). The change in LL when going from a standing to a lateral decubitus position (Delta LL), the correlation between standing and sitting LL compared to lateral decubitus LL, and the correlation between Delta LL and standing pelvic incidence (PI), pelvic tilt (PT), PI-LL mismatch, pelvic femoral angle (PFA), and sacral slope (SS) were calculated. Results Subjects had an average age of 25.7 +/- 2.3 years and body mass index of 24.1 +/- 3.0 kg/m2. On average, 11.9 degrees +/- 8.2 degrees (range - 7 degrees to 29 degrees) of LL was lost when transitioning from a standing to the lateral decubitus position. Lateral decubitus LL had a higher correlation with standing LL (R = 0.725, p < 0.001) than with relaxed-seated LL (R = 0.434, p < 0.001). Standing PT and PI-LL mismatch had moderately negative correlations with Delta LL (R=-0.58 and R=-0.59, respectively, both p < 0.05). Standing PI and standing PFA had a low negative correlation with Delta LL (R=-0.31 and R=-0.44, respectively, both p < 0.05) Standing SS and LL had no correlation with Delta LL. Conclusions Standing LL was strongly correlated to lateral decubitus LL, although subjects lost an average of 11.9 degrees from the standing to the lateral decubitus position. This has important implications for fusion in the lateral position.