Biomechanical Substantiation of Development and Progression of Structural Changes in Knee Joint
During kneehole surgeries after knee injury there are often determined structural changes of articular cartilage as areas of cartilage softening with its fluctuation. It is resulted by rapid water loss by collagen matrix and cartilage abruption from subchondrial bone. On the basis of imitating modeling by the finite elements method the mechanisms of destruction of a knee articulate cartilage in acute trauma and at further functional loading were studied. On a model of an articulate cartilage of the hip condyle the weakened site with a diameter of 10 mm with twice reduced mechanical properties, imitating a damage site, has been created. The maximum stress on a cartilage arise on the border of transition of different mechanical properties and on an articulate surface exceed levels in intact sites by 6.9 times, and on a subchondrial surface by 4.2 times. Stress concentrated in a zone of transition of properties on an intact site of a cartilage, whereas on a damaged site with the weakened properties the stress considerably lower though they are also located on the border of different properties. The maximum strain localized on the injured articulate cartilage with the changed mechanical properties. Because of it, on border of mechanical properties transition of the intact and injured cartilage there can be a pressed crack with further distribution of a zone of cartilage destructions. More considerable damaging influence occurs on mechanical properties transition area from an intact zone rather than a damage zone. The place of transition of intact cartillage to weakened one because of trauma becomes the concentrator of stress and a place of further destruction progressing of an articulate cartilage at cyclic loadings, with wide distribution of damaged area.