Knee radiographs are the first imaging modality performed in acute knee trauma, and in most of cases, the findings are obvious. Nevertheless, sometimes, only subtle clues can indicate a potentially more severe underlying abnormality, such as ligamentous, tendinous or meniscal tears. Knowledge of the origin of such signs and of the related underlying injury mechanism, might lead to additional imaging investigation, which may facilitate appropriate patient work-up and prevent consequences of delayed treatment.