Head Rotational Kinematics, Tissue Deformations, and Their Relationships to the Acute Traumatic Axonal Injury

Abstract

Head rotational kinematics and tissue deformation metrics obtained from finite element models (FEM) have the potential to be used as traumatic axonal injury (TAI) assessment criteria and headgear evaluation standards. These metrics have been used to predict the likelihood of TAI occurrence; however, their ability in the assessment of the extent of TAI has not been explored. In this study, a pig model of TAI was used to examine a wide range of head loading conditions in two directions. The extent of TAI was quantified through histopathology and correlated to the FEM-derived tissue deformations and the head rotational kinematics. Peak angular acceleration and maximum strain rate of axonal fiber and brain tissue showed relatively good correlation to the volume of axonal injury, with similar correlation trends for both directions separately or combined. These rotational kinematics and tissue deformations can estimate the extent of acute TAI. The relationships between the head kinematics and the tissue strain, strain rate, and strain times strain rate were determined over the experimental range examined herein, and beyond that through parametric simulations. These relationships demonstrate that peak angular velocity and acceleration affect the underlying tissue deformations and the knowledge of both help to predict TAI risk. These relationships were combined with the injury thresholds, extracted from the TAI risk curves, and the kinematic-based risk curves representing overall axonal and brain tissue strain and strain rate were determined for predicting TAI. After scaling to humans, these curves can be used for real-time TAI assessment.

Reproducibility and Characterization of Head Kinematics During a Large Animal Acceleration Model of Traumatic Brain Injury

“…Although heterogeneous in nature, most human traumatic brain injuries (TBI) are caused by the transmission of energy from an external force to the head that subsequently results in rapid acceleration/deceleration of the brain with or without deformation of the skull (1). Head kinematics have therefore been used to predict TBI pathology in both human and animal models, design safety equipment, and assess the risk of brain injury (2)(3)(4). However, to our knowledge, there have only been a handful of large animal studies that have used sensors (5)(6)(7)(8)(9) and/or high-speed cameras [see Table 1; (8,10,11)] to directly measure the magnitude of head kinematics during acceleration models of injury.…”

“…However, to our knowledge, there have been no large animal acceleration studies (see Table 1) establishing the reproducibility of head kinematics by either directly mounting a sensor to the animal's head or using high-speed video capture. The majority of previous studies have instead quantified kinematics from the machine used to produce the initial biomechanical forces and assumed a direct correspondence to subsequent head kinematics [e.g., (4)]. The five large animal studies to date that directly measured head kinematics with skull-mounted sensors varied the initial injury load conditions with no repeat tests (5)(6)(7)(8)(9).…”

“…Head kinematics are routinely used to drive finite element models of head impacts in both animal and human trauma scenarios. Finite element analyses indicate that the magnitude of axonal strains correlates with the velocity and direction of head rotation, moment of inertia, age, and brain size during acceleration ( 2 , 4 ). Therefore, having accurate measurements of the magnitude of head kinematics is a critical boundary condition for finite element analyses.…”

<p>Physiological Vibration Acceleration (Phybrata) Sensor Assessment of Multi-System Physiological Impairments and Sensory Reweighting Following Concussion</p>

“…This wide range of potential impairments arises from the corresponding wide range of potential impact-induced tissue damage locations, volumes, topologies, and affected CNS, PNS, sensory, vascular, and musculoskeletal structures. 2 A comprehensive objective assessment of these impairments is difficult to obtain, presenting significant challenges for concussion risk prediction, diagnosis, treatment, and rehabilitation. Although a variety of instrumented concussion assessment tools are available, there is no gold standard assessment tool and diagnosis of concussion remains a clinical decision.…”

“…123,124 The second factor is the relationship between displacement, velocity, and acceleration power spectral densities. Mathematically, displacement (d), velocity (v), and acceleration (a) all share the same spectral structure but with frequency-dependent scaling 125 2 . As a result, COP displacement spectra show significantly higher 1/f noise at lower frequencies and much steeper roll-off at higher frequencies than the corresponding velocity 85,126 and acceleration 31 spectra.…”