Bone anatomy

The human body consists over 200 bones.1-2 Bones are classified in long bones, short bones, flat bones and irregular bones. The femur and ulnae are examples of long bones. Long bones consist of epiphyses, the ends of the bone, and its diaphysis, the shaft of the bone. Short bones are cube shaped like the wrist and the ankle. Most of the skull bones and ribs are a bit curved, flattened and thin. These bones include the flat bones. Irregular bones include hipbones and vertebrae, these bones are complicated in shapes and not fit in the other classes.1-3 All bones consist of two different types of bone, compact bone and cancellous bone. Compact bone is dense and solid and found in the external bone surface and in the walls of the bone shaft. Compact bone looks like solid bone, however it has a porosity of 5 to 30% 3 due to osteons canals. Cancellous bone, also spongy bone, is present in de epiphysis and metaphysis of long bones. It looks like a poorly organized tissue. However, in spongy bone the trabeculae are aligned along the stress lines and it helps bones to resist stress.1,2,4 Spongy bone has a porosity of 30% to more than 90% 3 due to bone marrow intertrabecular and vascular space. Both cortical and trabecular bone are composed of osteons. Osteon in cortical bone called Haversian systems and are cylindrical in shape. The cylinder form is orientated parallel to the long axis of the bone. An osteon consists of layers of lamella around the central canal. The lamella consists of collagen with each different direction. These different directions of collagen fibers (anisotrophy) enable bone to resist torsion strength. The central canal consists of nerve fibers and small blood vessels. Osteons are connected to each other with vascular canals, Volksmann’s canals, which arise from endosteum and periosteum.1,4,5 The periosteum is a double layered membrane surrounds the external surface of the bone except for the joints surfaces.1-2