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.

Personalised gravitational loading of the cervical spine from biplanar X-rays for asymptomatic and clinical subjects in neutral standing position.

BACKGROUND: As a leading cause of disability with a high societal and economic cost, it is crucial to better understand risk factors of neck pain and surgical complications. Getting subject-specific external loading is essential for quantifying muscle forces and joint loads but it requires exertion trials and load cells which are uncommon in clinical settings. METHODS: This paper presents a method to compute the gravitational loading at four levels of the cervical spine (C3C4, C4C5, C5C6, C6C7) in neutral standing position from biplanar radiographs exclusively. The resulting load was decomposed in local disc frames and its components were used to compare different populations: 118 asymptomatic subjects and 46 patients before and after surgery (anterior cervical discectomy and fusion or total disc replacement). Comparisons were performed at C6C7 and the upper level adjacent to surgery. FINDINGS: Significant changes in gravitational loading were observed with age in healthy subjects as well as in patients after surgery and have been associated with changes in posture. INTERPRETATION: This approach quantifies the influence of postural changes on gravitational loading on the cervical spine. It represents a simple way to obtain necessary input for muscle force quantification models in clinical routine and to use them for patient evaluation. The study of the subsequent subject-specific spinal loading could help further the understanding of cervical spine biomechanics, degeneration mechanisms and complications following surgery.