Whole-spine dynamic magnetic resonance study of contortionists: anatomy and pathology

Beyond the Bony Fragment: A Review of Limbus Vertebra

Vertebral limbus is a condition characterized by the intraspongious herniation of a portion of the nucleus pulposus. It is often asymptomatic, but it can sometimes cause nonspecific symptoms such as local pain and muscle spasm, or, in rare cases, radiculopathies, which is why it can be confused with vertebral fractures, spondyloarthropathies, infectious or tumoral processes. Early recognition of this pathology is preferable for a correct diagnosis and adequate treatment, the latter ranging from conservative approaches (such as personalized exercise programs and physical therapy) to surgical interventions reserved for severe cases with nerve compression.

Understanding the fluid mechanics behind transverse wall shear stress

The patchy distribution of atherosclerosis within arteries is widely attributed to local variation in haemodynamic wall shear stress (WSS). A recently-introduced metric, the transverse wall shear stress (transWSS), which is the average over the cardiac cycle of WSS components perpendicular to the temporal mean WSS vector, correlates particularly well with the pattern of lesions around aortic branch ostia. Here we use numerical methods to investigate the nature of the arterial flows captured by transWSS and the sensitivity of transWSS to inflow waveform and aortic geometry. TransWSS developed chiefly in the acceleration, peak systolic and deceleration phases of the cardiac cycle; the reverse flow phase was too short, and WSS in diastole was too low, for these periods to have a significant influence. Most of the spatial variation in transWSS arose from variation in the angle by which instantaneous WSS vectors deviated from the mean WSS vector rather than from variation in the magnitude of the vectors. The pattern of transWSS was insensitive to inflow waveform; only unphysiologically high Womersley numbers produced substantial changes. However, transWSS was sensitive to changes in geometry. The curvature of the arch and proximal descending aorta were responsible for the principal features, the non-planar nature of the aorta produced asymmetries in the location and position of streaks of high transWSS, and taper determined the persistence of the streaks down the aorta. These results reflect the importance of the fluctuating strength of Dean vortices in generating transWSS.