In the Netherlands, 34% of all major lower limb amputations are at the trans-femoral level. Information and consensus is lacking on the optimal length of the residual length of the femur following the amputation. HYPOTHESIS: We hypothesize that femur length should be kept as long as possible considering construction of the knee unit beneath the socket. Evaluation of the hypothesis: Providing a comprehensive overview of considerations involved in choosing the optimal femur length in a trans-femoral amputation. This explorative study includes a scoping review, interviews with surgeons and certified prosthetists (expert opinions), and a biomechanical analysis. The scoping review resulted in 396 articles reduced to 6 articles after reviewing. All articles, the outcomes of the interviews with the experts and the biomechanical analysis suggest that it is important to maximize the length of the residual femur. CONCLUSION: A longer residual limb length is more beneficial for gait parameters, prevention of contractures, and providing lever arm. Furthermore, the femur should be transected sufficiently proximal to the medial knee joint in order to fit a prosthetic knee at the same height as the contralateral knee. However, it remains unclear what the minimum length of the residual limb should be. This will require further research.