Reproducibility of assessing rib cage mobility from computed tomography images.

Background: Rib cage mobility decreases in various health conditions, for example neuromuscular diseases. A decrease in rib cage mobility reduces respiratory function and therefore increases the risk of respiratory complications. To evaluate the effects of interventions aiming at increasing rib cage mobility, changes should be calculated from measurements before and after such interventions. Therefore, an accurate and easy to perform method is needed.

Objective: To assess rib cage mobility using computed tomography (CT).

Methods: We analysed single-image CT scans of the chest to assess its reproducibility at maximal inspiration and expiration in ten able-bodied individuals and ten subjects with tetraplegia. CT scans were taken twice in the supine position, with a repositioning of subjects in-between. At maximal inspiration and expiration, two images at the fourth and ninth vertebral body were recorded. Intra-costal areas, anterior-posterior distances from the sternum to the vertebral body as well as transversal distances of the chest were measured manually by three independent testers, each of them analysing all data twice. Intra-class correlation coefficients (ICCs) and Bland and Altman plots were calculated for intra-subject reproducibility at maximal inspiration and expiration as well as for intra- and inter-tester reproducibility.

Results: Mean differences between the two intra-subject measurements expressed as percentage of their mean were 2.3 ± 1.3% in able-bodied individuals and 2.1 ± 1.3% in subjects with tetraplegia. All ICCs were above 0.95 and thus showed very high reproducibility.

Conclusion: Assessing rib cage mobility by analysing CT scans of the chest is a simple and highly reproducible method.