Notching of the anterior femoral cortex during primary total knee arthroplasty can occur when making an anterior femoral bone cut. To examine the increased stress caused by a notch, we used a validated 3-dimensional finite element model of the femur under gait loads. Three factors that affected the stress concentration were identified: First, larger notches associated with increased stress concentrations. Second, sharper notches led to increased local stresses. Third, the proximity of the notch to the prostheses affected the stress concentration. In summary, anterior femoral notches greater than 3 mm with sharp corners located directly at the proximal end of the prosthesis produced the highest stress concentrations and may lead to a significant risk of periprosthetic fracture.