A biomechanical enigma: Why are tibial fractures not more frequent in the elderly?

Epidemiology revealed that diaphyseal fractures of the tibia affect young p eople, particularly young men; no increase was noticed for the elderly. Thi s indicates that osteoporosis does not lead to increased bone fragility. Ob viously, this is a biomechanical enigma. Torque measurements were carried out on human cadaveric tibiae and revealed a great correlation between the polar moment of inertia of the cortical bo ne at the tibial isthmus and the ultimate torque at failure (r = 0.83) and a lesser correlation between the cross-sectional density at the isthmus and the torque at failure (r = 0.57). Therefore, the size is more important th an the degree of osteoporosis. We can speculate that endosteal resorption due to osteoporosis is compensat ed for by periosteal apposition and therefore does not lead to bone weaknes s.