[Impact absorbing properties of the human knee joint]

A biomechanical study has been carried out on 20 cadaveric knee joints to investigate the load absorbing mechanism of the knee. The impact load was applied using a falling weight onto the transected proximal femur and the force transmitted through the knee joint was measured at the transected distal tibia using a load transducer. The transmitted peak force applied through the joint was first measured through the intact knee (100%). After the lateral and medial menisci were cut radially the transmitted peak force increased to 113% and it reached 121% after the meniscus and all the soft tissues had been removed. Next the articular cartilage and subchondral bone were removed and this resulted in the transmitted peak force increasing to 135%. When a knee joint replacement was then carried out, the peak transmission force was found to increase to 180%. These results show that the knee joint has an impact absorbing property in each segment and comparison of the results reveals that osteoarthritic joint is capable of less shock absorption than the normal knee. The high impact force in an implanted knee suggests micro-fractures of the cancellous bone might be expected and may produce long term loosening.