The rib cage: a new element in the spinopelvic chain

Introduction: This study analyzes anatomical variations of the thoracic cage (TC) according to spinopelvic alignment, age and gender using stereoradiography in erect position. Methods: This retrospective multicentric study analyzed computed parameters collected from free-standing position bi-planar radiographs, among healthy subjects. Collected data were: age, gender, pelvic parameters (Pelvic Incidence, Pelvic Tilt (PT) and Sacral Slope), T1-T12 Kyphosis (TK), L1-S1 Lordosis (LL), curvilinear spinal length, global TC parameters (maximum thickness and width, rib cage volume, mean Spinal Penetration Index (SPI)), 1st–10th rib parameters (absolute and relative (to the corresponding vertebra) sagittal angles). Results: Totally, 256 subjects were included (140 females). Mean age was 34 (range: 8–83). Significant correlations were found between TK and TC thickness (0.3, p < 0.001) and with TC Volume (0.3, p = 0.04), as well as rib absolute sagittal angle for upper and middle ribs (0.2, p = 0.02). Conversely, a −0.3 correlation has been exhibited between SPI and TK. Similar correlations were found with LL. PT significantly correlated with TC thickness (0.4, p = 0.003), SPI (−0.3, p = 0.03), and all rib relative sagittal angles. Among global TC parameters, only thickness and SPI significantly changed after 20 years (respectively, 0.39 and −0.52, p < 0.001). Ribs relative sagittal angle showed negative correlation with age in skeletally mature subjects (p < 0.001). Conclusion: This study demonstrates the correlation between TC anatomy and spinopelvic parameters, confirming its part of the spinopelvic chain of balance. Indeed, higher spinal curvatures were associated with lower SPI and higher TC thickness, TC volume and rib absolute sagittal angles