Mechanism and healing of a bone fracture

Mechanism and healing of a bone fracture

Bone is a living, cellular tissue capable of growth, self-repair and continuous remodeling in response to physical stress — in the adult skeleton, bone deposition and bone resorption occur side by side as part of normal maintenance. Repairing a simple fracture proceeds through four well-defined stages (Figure 9.15):

Step 1. Formation of haematoma. When a bone breaks, the blood vessels within the bone and the surrounding tissue tear, causing haemorrhage. The pooled, clotted blood forms a haematoma at the fracture site; the surrounding tissue becomes swollen, painful and inflamed, and some bone cells at the site die from the resulting loss of nutrition.

Step 2. Formation of fibrocartilaginous callus. Within a few days, capillaries grow into the haematoma and phagocytic cells move in to clear away debris, while fibroblasts and osteoblasts migrate in from the nearby periosteum and endosteum to begin reconstruction. Fibroblasts lay down connective fibres, and chondroblasts secrete a cartilage matrix; within this soft granulation tissue, osteoblasts also begin forming spongy bone. The cartilage matrix eventually calcifies, forming the soft fibrocartilaginous callus.

Step 3. Formation of bony callus. New spongy-bone trabeculae begin appearing within the fibrocartilaginous callus, gradually converting it into a harder bony callus made of spongy bone. This process continues until a firm union forms, typically taking about two months up to a year for complete bone re-formation. …