The Lower Leg Impactor (LLI) has been used since 2005 without any modification. However, this model lacks similitude with the human knee. This work analyzes the operation of a four-bar mechanism applied in LLI, as a movable element of the knee. In addition, Runover experimental tests were carried out using the LLI made with ultra-high molecular weight polyethylene (UHMWPE), to analyze the accuracy of movable knee implemented in the LLI under the European Enhanced Vehicle-Safety Committee/Working Group 17 (EEVC/WG17) standard. The results show the possible injuries suffered in the double four-bar mechanism and the different injuries developed in pedestrians.