Developing a new knee prosthesis requires thorough testing. Forward dynamics simulation can be valuable in the development process. It can reduce the need for intermediate prototypes and tests. Currently, there are 3D simulations of healthy walking and kinematic models of common prosthesis like the 3R60. However, they have not yet been combined. Such a model could function as a baseline for newly developed prostheses. It would also open possibilities for researchers to modify the prosthesis design by analyzing different scenarios in simulations. In this paper an existing 3D neuromuscular model of a healthy human is adjusted so that it represents a trans-femoral amputee with a 3R60. The model is simulated walking with an average velocity of 0.9 m/s and 1.2 m/s. The performance of the model is evaluated by comparing gait differences between the healthy and amputee model to findings from literature. The simulated amputee gait agrees well with literature, especially for a velocity of 1.2m/s. When walking 0.9 m/s the model oscillates in the coronal plane, suggesting it has difficulty maintaining balance. Furthermore, a case study was done on fall prevention using a control moment gyroscope embedded in the prosthetic shank. The control moment gyroscope increases the ability to flex and extend the prosthetic knee, which can help with fall prevention. With the added control moment gyroscope the gait at 1.2 m/s became more symmetric. A fall was prevented after a trip using a control moment gyroscope, however, this simulation is numerically too sensitive to draw conclusions.