Lateral impacts correlate with falx cerebri displacement and corpus callosum trauma in sports-related concussions

Abstract

Corpus callosum trauma has long been implicated in mild traumatic brain injury (mTBI), yet the mechanism by which forces penetrate this structure is unknown. We investigated the hypothesis that coronal and horizontal rotations produce motion of the falx cerebri that damages the corpus callosum. We analyzed previously published head kinematics of 115 sports impacts (2 diagnosed mTBI) measured with instrumented mouthguards and used finite element (FE) simulations to correlate falx displacement with corpus callosum deformation. Peak coronal accelerations were larger in impacts with mTBI (8592 rad/ s 2 avg.) than those without (1412 rad/s 2 avg.). From FE simulations, coronal acceleration was strongly correlated with deep lateral motion of the falx center (r = 0.85), while horizontal acceleration was correlated with deep lateral motion of the falx periphery (r > 0.78). Larger lateral displacement at the falx center and periphery was correlated with higher tract-oriented strains in the corpus callosum body (r = 0.91) and genu/splenium (r > 0.72), respectively. The relationship between the corpus callosum and falx was unique: removing the falx from the FE model halved peak strains in the corpus callosum from 35% to 17%. Consistent with model results, we found indications of corpus callosum trauma in diffusion tensor imaging of the mTBI athletes. For a measured alteration of consciousness, depressed fractional anisotropy and increased mean diffusivity indicated possible damage to the mid-posterior corpus callosum. Our results suggest that the corpus callosum may be sensitive to coronal and horizontal rotations because they drive lateral motion of a relatively stiff membrane, the falx, in the direction of commissural fibers below.

Influence of the corpus callosum anatomy on its mechanical behavior during a lateral impact. A finite element study

“…In other words, the Von Mises stress decreases the closer CC is to the free edge of the FC. This trend seems to contradict the conclusion of Hernandez et al (2019) who showed that the strain in the CC decreased (from 0.37 to 0.17) in simulations without taking the FC into account. Nevertheless, FC is a rigid element in the centre of the cranial cavity that limits lateral movement of the brain; without it, the CC is free to move and is then less stressed.…”

“…On impact, mechanical loading of the corpus callosum was shown to be strongly associated with the occurrence of concussion (Jang et al 2019). In addition, a recent study based on finite element simulation of lateral impacts on the head, has demonstrated the influence of the interaction between the falx cerebri and the corpus callosum on its mechanical loading (Hernandez et al 2019). However, the relationship between this local anatomy and these mechanical loads has not yet been analysed.…”

Novel strain analysis informs about injury susceptibility of the corpus callosum to repeated impacts

“…Existing literature from finite element modelling of head impacts support these findings in showing that the CC is relatively tethered by the anatomy of the falx cerebri ( Hernandez et al , 2019 ), which may affect the direct transfer of rotational forces to the tissues, and induce more shearing injury of the WM fibre tract. Although the central attachment of the falx may provide some structural stability, differences in fibre compositions (i.e.…”

“…In recent years, advances in computational modelling of head injuries have identified the corpus callosum (CC) as a fibre tract with high injury susceptibility ( McAllister et al , 2012 ; Stamm et al , 2015 ; Hernandez et al , 2019 ). As the largest commissural fibre tract in the brain, the density and fibre orientation of the CC appear to make this WM tract more vulnerable to diffuse axonal injury ( Johnson et al , 2012 ; McAllister et al , 2012 ; Beckwith et al , 2018 ; Hernandez et al , 2019 ), due to the increased shear forces transferred locally, upon exposure to external acceleration/deceleration forces. Preliminary evidence from impact biomechanics ( McAllister et al , 2012 ; Hernandez et al , 2019 ) suggests that differences in sub-structures within the anatomy of the CC, along with heterogeneity in the deformation fields induced from mechanical loading, may contribute to the increased susceptibility of the CC for changes in WM integrity.…”

“…As the largest commissural fibre tract in the brain, the density and fibre orientation of the CC appear to make this WM tract more vulnerable to diffuse axonal injury ( Johnson et al , 2012 ; McAllister et al , 2012 ; Beckwith et al , 2018 ; Hernandez et al , 2019 ), due to the increased shear forces transferred locally, upon exposure to external acceleration/deceleration forces. Preliminary evidence from impact biomechanics ( McAllister et al , 2012 ; Hernandez et al , 2019 ) suggests that differences in sub-structures within the anatomy of the CC, along with heterogeneity in the deformation fields induced from mechanical loading, may contribute to the increased susceptibility of the CC for changes in WM integrity. Despite these findings however, research combining both DTI and in vivo measurements of tissue material properties is currently limited, which has constrained our understanding of the relationship between changes in tissue integrity and geometry following exposure to repeated head impacts.…”