The importance of femoral intramedullary entry point in knee arthroplasty

The purpose of this cadaveric study was to investigate how alignment of the femoral component in knee arthroplasty may be influenced by the entry site of the femoral intramedullary alignment rod. The angle between the rod and the distal femoral articular surface was measured in 20 non-arthritic cadaveric femurs using three different entry points. Entry points 10 mm anterior to the intercondylar notch and 8 mm medial to this point gave mean valgus angles of 8° (S.D. 1.0) and 10.2° (S.D. 1.0), respectively. Regression analysis showed no relationship between sex of the patient, body habitus, or leg length and valgus angulation of the distal femur. For total knee replacement in which the tibia is cut perpendicular to its axis in the coronal plane, thus eliminating 3° of tibial varus, we recommend using a femoral valgus angle of 5° with a hole anterior to the intercondylar notch and 7° with an anteromedial hole. Resecting the distal femur as recommended should enhance accuracy of component placement and survival of knee arthroplasties.