PHYSIOLOGY EXPLAINED: FRACTURE HEALING
When you break a bone, blood vessels in the bone marrow and periosteum rupture and cause a hematoma in the fractured area. Because the local blood vessels are severed, there is no sufficient delivery of nutrients to osteocytes at the ends of the broken bones and necrosis occurs. Within minutes after the injury, a hematoma forms, this is very important because it is a condition for entering the next stage of tissue repair.
Cytokines and tissue hormones that are released from the site of the injury signal monocytes and macrophages to clean up tissue debris and dead cells. (Small fractures that were initially missed on an x-ray can be seen later because of this “cleaning up”) This stage takes about two to five days, but bone splinters take longer to clean up.
After just a day bone forming cells start multiplying rapidly and a little later they start migrating to the site of the fracture. After two days blood vessels from the periosteum and the bone marrow can be seen entering the hematoma. Over the next couple of days, rapid multiplication of capillaries, fibroblasts, chondroblasts and osteoblasts occurs. From the fourth day small islands of chondroblasts and osteoblasts start forming a matrix. At the end of the first week a soft callus starts to form, this callus is made of matrix, collagen, blood vessels and an early stage of bone. Mineralization starts a little later, in one to three weeks bridges of bone between the fracture sites can be found, good perfusion facilitates this bridge formation. Mineralization continues until a hard callus is formed, this typically takes several weeks to months, depending on certain variables.
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