Traumatic Brain Injuries (TBIs) are a pressing global public health issue, impacting tens of millions of individuals annually. Vulnerable road users (VRUs), such as pedestrians, are vastly overrepresented in the worldwide TBI statistics. To evaluate the effectiveness of injury prevention measures, researchers often employ Finite Element (FE) models of the human body to virtually simulate the human response to impact in real-world road traffic accident scenarios. However, VRU accidents occur in a highly uncontrolled environment and, in consequence, there is a large amount of variables (covariates), e.g. the vehicle impact speed and VRU body posture, that together dictate the injurious outcome of the collision. At the same time, since FE analysis is a computationally heavy task, researchers often need to apply extensive simplifications to FE models when attempting to predict real-world VRU head trauma. To help researchers make informed decisions when conducting FE accident reconstructions, this literature review aims to create an overarching summary of covariates that have been reported influential in literature. The review provides researchers with an overview of variables proven to have an influence on head injury predictions. The material could potentially be useful as a basis for choosing parameters to include when performing sensitivity analyses of car-to-pedestrian impact simulations.