The femur, or thigh bone, is the longest, heaviest, and strongest bone in the entire human body. All of the body’s weight is supported by the femurs during many activities, such as running, jumping, walking, and standing. Extreme forces also act upon the femur thanks to the strength of the muscles of the hip and thigh that act on the femur to move the leg. The femur is classified structurally as a long bone and is a major component of the appendicular skeleton.
Bone is living tissue and has a hard, relatively rigid matrix. The matrix contains numerous collagen fibres and is
impregnated with inorganic salts, primarily calcium phosphate. Compact bone is composed of numerous structural units called Haversian systems. Each Haversian system is seen as a nearly round area. The circular core of each system is the Haversian canal that runs lengthwise through the bone. Blood vessels and nerves run through the Haversian canals. Around the Haversian canal is a series of concentrically arranged hard lamellae, perforated by elongate dark areas, called lacunae, in which the bone cells (osteocytes) are located. The numerous very thin dark lines running radially from the central canal across the lamellae to the lacunae are the canaliculi. These channels connect the bone cells to one another and to the Haversian canal. They provide the "highways" through which tissue fluid, oxygen, and nutrients can reach the widely separated bone cells, imprisoned as they are in a desert of solid matrix.
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