Reassessment of two finite-element studies of infant head trauma: limits of the modelling evidence for shaking-induced bridging-vein rupture and protection by enlarged subarachnoid spaces.

Introduction: Finite-element (FE) models are often invoked to study infant head trauma where direct experimentation is impossible, but their evidentiary value depends on credible geometry, loading, constitutive assumptions, verification, and validation. We present a biomechanical reassessment of two influential FE studies published in 2007 and 2008 that concluded, respectively, that shaking without impact can produce bridging-vein loading comparable to impact and that benign enlargement of the subarachnoid space (BESS) protects against subdural hemorrhage. Methods: Treating these papers as modelling evidence, we re-examined their reported geometry, loading, vein representation, and inferential logic in light of later work on infant head kinematics, bridging-vein morphology and mechanics, and pediatric FE credibility. Results: Neither paper reported mesh or parameter sensitivity, validated brain motion or venous response, or demonstrated that the implemented loads reproduced the head kinematics of the surrogate experiments used to justify them. The shaking input was inherited from a worst-case surrogate with a resistance-free sagittal hinge neck, whereas the comparison impact was a lower-severity, non-rotational loading condition. Bridging veins were represented as straight linear springs, and the BESS analysis depended on a zero pre-strain assumption that is not biologically valid. Discussion: These limitations mean that the two studies do not provide robust modelling support for the claims that shaking alone produces impactequivalent bridging-vein loading or that enlarged subarachnoid spaces protect against subdural hemorrhage. We conclude by identifying minimum credibility requirements for pediatric FE studies used to support forensic or clinical inference.