骨折：骨の修復

Bone fracture repair occurs in three stages: reactive, reparative, and remodeling. The reactive phase seals damaged blood vessels, forming a fracture hematoma that triggers inflammation and recruits immune cells. The reparative phase involves fibroblasts and chondroblasts forming soft callus tissue, while osteoblasts create spongy bone trabeculae. Finally, the remodeling phase replaces peripheral spongy bone with compact bone, restoring the bone's structural integrity.

During the reactive phase, damaged blood vessels form a blood clot called fracture hematoma. This disrupts circulation, causing bone cells near the fracture to die. The resulting cell debris triggers swelling and inflammation, recruiting phagocytes and osteoclasts to the injury site. As debris is cleared, new blood vessels extend into the hematoma, initiating the reparative phase.

During the reparative phase, fibroblasts and chondroblasts migrate from undamaged bone regions into the fractured gap. These cells form collagen fibers and fibrocartilage, creating soft callus tissue that bridges the broken ends. This temporary repair tissue provides structural support while osteoprogenitor cells differentiate into osteoblasts to begin forming spongy bone trabeculae at the fracture margins.

Closed reduction involves manual positioning of fractured bone ends without surgery, while open reduction surgically aligns and secures fractured bone ends using devices like screws, wires, rods, and plates. The choice depends on fracture type, bone affected, and patient age. After reduction, bones are immobilized using casts, splints, slings, bandages, or external fixation devices for proper healing.

Epiphyseal fractures involve the growth plate and require prompt treatment to prevent premature closure. If untreated, the growth plate may close prematurely, stopping bone growth. For example, a tibial growth plate fracture in a child can cause skeletal deformities, resulting in the affected leg being shorter than the healthy leg as the child grows.

During the remodeling phase, osteoclasts and osteoblasts work together to reshape the fracture site. Osteoclasts remove peripheral spongy bone while osteoblasts replace it with compact bone, restoring the bone shaft wall. This coordinated remodeling process, similar to bone formation endochondral ossification, gradually replaces the hard callus with mature bone tissue, fully restoring structural integrity.

Open fractures that penetrate the skin require urgent medical care to prevent excessive bleeding and infection. These fractures demand immediate intervention beyond standard immobilization. In contrast, minor fractures with no bone displacement are simply immobilized using a cast or splint. The severity and type of fracture determine whether closed reduction, open reduction, or emergency intervention is necessary.