Notching in the anterior femur with use of femoral stem: a finite element study

Abstract

Risk factors for the occurrence of distal femoral fracture after total knee arthroplasty include osteopaenia, osteoporosis, anterior femoral notching, total knee revision arthroplasty and severe neurological disorders. Some investigators suggest that patients who sustain inadvertent notching should have additional protection in the postoperative period, and that consideration should be given to the use of prophylactic femoral stem extensions as a way to bypass the stress-riser of the anterior notch. In this particular case, one question concerning the structural aspects of the use of prophylactic femoral stems in inadvertent notching can be raised, namely, what is the range of notch size where the use of a femoral stem can be useful to reduce fracture risk? The insight offered by the present study through the use of finite element models suggests an increase of risk of supracondylar fracture for notch depths greater than 4 mm. The use of a femoral stem reduces the peak strains within the notch region and consequently reduces the risk of bone fracture, however the use of a stem also reduces strains in the other bone regions, which can promote osteopaenia. The use of prophylactic stems for notch depths greater than 4 mm is helpful and should be considered in cases where the bone quality is good. In the cases of a notch deeper than 4 mm in patients with evident signs of osteopaenia, the use of a stem should be avoided and it seems to be prudent to protect such a patient’s implant from bearing weight.