What bones are made of

“Thank goodness it’s only a fracture. I thought it might be broken.” People often think that a fracture is less severe than a broken bone, but fractures are broken bones.

To understand why bones break, it helps to know what bones do and what they are made of. The bones of the body form the human frame, or skeleton, which supports and protects the softer parts of the body. Bones are living tissue. They grow rapidly during one’s early years, and renew themselves when they are broken.

Bones have a center called the marrow, which is softer than the outer part of the bone. Bone marrow has cells that develop into red blood cells that carry oxygen to all parts of the body and into white blood cells that help fight disease. Bones also contain the minerals calcium and phosphorus. These minerals are combined in a crystal-like or latticework structure. Because of their unique structure, bones can bear large amounts of weight.

How fractures occur

Bones are rigid, but they do bend, or “give” somewhat when an outside force is applied to them. When this force stops, bone returns to its original shape. For example, if you fall forward and land on your outstretched hand, there’s an impact on the bones and connective tissue of your wrist as you hit the ground. The bones of the hand, wrist and arm can usually absorb this shock by giving slightly and then returning to their original shape and position. If the force is too great, however, bones will break, just as a plastic ruler breaks after being bent too far.

Types of fractures

The severity of a fracture usually depends on the force that caused the fracture. If the bone’s breaking point has been exceeded only slightly, then the bone may crack rather than breaking all the way through. If the force is extreme, such as in an automobile collision or a gunshot, the bone may shatter. If the bone breaks in such a way that bone fragments stick out through the skin or a wound penetrates down to the broken bone, the fracture is called an “open” fracture. This type of fracture is particularly serious because once the skin is broken, infection in both the wound and the bone can occur.

See Casts & Splints