Femoral neck fractures frequently occur in elderly patients and the treatment strategies for this are well documented. Revision knee arthroplasty using a long intra-medullary stem has recently been increasingly used for treating complications such as infection, aseptic loosening or instability. The current case had a femoral neck fracture with a well-fixed, long stem knee prosthesis, which reached to near the lesser trochanter of the femur. The authors performed the surgery using impaction of the modular hip segment; its inner diameter was fit to the outer diameter of the femoral stem of the knee prosthesis. At two years postoperative follow-up, the result was excellent without loosening or osteolysis.