This article reports a case of the blunt open injury to the lower extremities resulting from the overextension of the knee joint that, despite it severity, turned out to be a mere accompanying event of a more serious condition. This case is of great interest in the context of forensic medical expertise by virtue of the apparent discrepancy between the extent of the injury and the circumstances of the accident. Clearly, such discrepancy may influence the reliability of the expert conclusion as regards the evaluation of such injury.