What does the shape of our back tell us? Correlation between sacrum orientation and lumbar lordosis.

Abstract

Sacral slope and lumbar lordosis (LL) have been studied extensively in recent years via X-ray examinations and strongly correlate with each other. This raises, first, the question of the reproducibility of this correlation in multiple standing phases and, second, if this correlation can be achieved using non-radiological measurement tools. This study aimed (1) to determine the extent to which the back-shape measurements correspond to the correlations between the sacral slope and LL found in previous radiological investigations, (2) to identify a possible effect of age and gender on this correlation, and (3) to evaluate the extent to which this correlation is affected by repeated standing phases. This is an observational cohort study. A total of 410 asymptomatic subjects (non-athletes), 21 asymptomatic soccer players (athletes), and 176 patients with low back pain (LBP) were included. The correlation between sacrum orientation (SO) and LL was determined in six repetitive upright standing postures. A non-invasive strain-gauge based measuring system was used. Back-shape measurements yielded a similar correlation to that measured in previous X-ray examinations. The coefficient of determination (R²) between SO and LL ranged between 0.76 and 0.79 for the asymptomatic cohort. Athletes showed the strongest correlation (0.76≤R²≤0.84). For patients with LBP, the correlation substantially decreased (0.18≤R²≤0.39). R² was not strongly affected by repeated standing phases. The correlation between SO and LL can be assessed by surface measurements of the back shape and is not influenced by natural variations in the standing posture.