Section through the lower (distal) end of the human femur or upper leg bone that forms part of the knee. The bone has been sectioned to show the trabeculae that form the internal supportive structure of long bones. The ends of long bones are filled with trabeculae and are called spongy or cancellous bone. In old age, the density of trabeculae decreases (osteoporosis) and the bones become vulnerable to fracture.