Biomechanics of distal femoral fracture fixed with an angular stable LISS plate

Fractures of the distal end of the femur are infrequent and constitute less than 1% of all fractures. Only 3% to 6% of femoral fractures occur at the distal end. The two groups most at risk of the said fractures are young men and older women. The aim of treatment of fractures of the distal femur is to restore normal function of the knee joint. The authors asked themselves whether, following fixation of a 33-C2 fracture (according to the AO classification) with a LISS plate, a rehabilitation program can be undertaken immediately after surgery with the implementation of active movements in the knee joint of the operated limb. In order to answer this question, we created a digital model of a fractured femur fixed with the LISS method. The model was subjected to loads corresponding to the loads generated during active lifting of a limb extended in the knee joint and during flexing of a limb in the knee joint to the 90° angle. Interfragmentary movement (IFM) is one of the key parameters taken into account in the treatment of bone fractures. It allows classification of the treatment in terms of its quality both from the mechanical and histological points of view. We analyzed interfragmentary movement in all fracture gaps. The largest recorded displacement reached in our model was 243 μm, which, in the light of the literature data, should not interfere with bone consolidation, and thus implementation of active movement in the operated knee joint (keeping in mind the simplifications of the experimental method used) is possible in the early postoperative period.