Survival characteristics of forty-three specimens of living human bone
and articular cartilage from the knees of eight renal-transplant donors
were studied, using a drop-tower device. Autoradiography and light and
scanning electron microscopy revealed no evidence of chondrocyte death or
structural damage until stress levels of twenty-five newtons per square
millimeter were reached, corresponding to strains on the order of 20 to 30
per cent and involving energy absorption of one millijoule per cubic
millimeter. The data for strain rates of 500 and 1000 s-1 suggest that
impact loads sufficient to fracture a femoral shaft of an automobile
occupant are nearly sufficient to cause chondrocyte death and fissuring in
the articular cartilage of either the knee or the hip if the load-bearing
areas measure less than 500 square millimeters.