Lori Evert, age 11, of St. Paul, Minn., for her question:
HOW DOES A BROKEN BONE HEAL?
A healthy human body performs a multitude of large and small miracles every day. We are not surprised with a skin scratch that heals, or when a properly tended flesh wound repairs itself. But surely a broken bone must be a major disaster. Actually, the body does need some outside assistance, and the repair work takes a long time. But the final result is as good as new.
A hard, brittle bone is an active, growing part of the busy body and very much alive. It has a soft center stuffed with marrow and an outer sheath of double membrane. These portions contain nourishing blood vessels, and the marrow contains centers where various blood cells are manufactured for the entire body. This rich blood seeps into pores throughout the stiff bony substance. And such healthy blood supplies are needed in all healing
A bone also contains special cells called osteocytes that produce a tough protein called collagen. Throughout the body, collagen is used to build hair, tendons and a thin tough web that connects all the soft tissues. The collagen manufactured by osteocytes in the bone has a special quality. It can attract tough calcium phosphate to build durable fibers for bone mending cement.
When a bone is fractured, the broken edges must be set by an expert and the whole thing sealed in a cast during the mending operation. The blood that seeps from the broken edges soon clots and forms rubbery pads. Then the osteocytes build a rubbery wad called a callus, uniting the broken ends.
More and more collagen is produced to build tough fibers that weave through the callus. Gradually this rubbery wad is reinforced with calcified material and becomes a bridge of new bone material. When at last the repair work is completed, the rebuilt bone is as strong and sometimes stronger than the original.
As you can imagine, the broken ends must be held in place or the repair work may result in a crooked bone. This is why a fracture is set by an expert and sealed in a cast. And the victim must be extra patient because the complex mending miracle may take several months