Biomechanical behaviour at the distal third of the femur: Possible use of a medial metaphyseal plate

The incidence of fractures in the distal femur is becoming more frequent and they are often associated to complex lesions with potential complications. Operative treatment is mandatory for elderly people and several methods of internal fixation with appropriate implants have been developed, generally approaching the lateral aspect of femur. An alternative antero-medial access was proposed several years ago but the biochemical aspects of its application must be debated. The aim of the present study is to establish if adverse biomechanical effects should be expected when the plate is affixed at the medial site of the femur metaphysis, by analysing the strain pattern of a human cadaver femur submitted to loads simulated in different experimental conditions. Application of load resulted, as expected, in tension in the lateral aspect and compression in the medial aspect of the femur diaphysis, but it turned more and more toward the anterior aspect when the levels measured changed from proximal to distal. The plate was next to the neutral axis and produced a moderate stress protection effect (approx. 70 per cent). No biochemical disadvantages have been observed as a result of the plate being apposed at the medial aspect instead of the conventional lateral aspect of the distal femur.