Almost a decade ago, three-dimensional formulation for the dynamic modeling of an articulating human joint was introduced. Two-dimensional version of this fomulation was subsequently applied to the knee joint. However, because of the iterative nature of the solution technique, this model cannot handle impact conditions. In this paper, alternative solution methods are introduced which enable investigation of the response of the human knee to impact loading on the lower leg via an anatomically based model. In addition, the classical impact theory is applied to the same model and a closed-form solution is obtained. The shortcomings of the classical impact theory as applied to the impact problem of the knee joint are delineated.