A&P Bone Repair

Fracture Hematoma

First step in bone repair. Blood clots, due to blood vessels within the break being torn.

Bone Remodeling

Fourth step in bone repair. The hard callus persists for at least 3 to 4 months, as osteoclasts remove excess bony material from both exterior and interior surfaces. Compact bone replaces primary bone. The fracture usually leaves a slight thickening of the bone (as detected by x-ray); however, in some instances healing occurs with no persistent obvious thickening.

Fibrocartilaginous (Soft) Callus

Second step in bone repair. Regenerated blood capillaries infiltrate the fracture hematoma due to an increase in osteoblasts in both the periosteum and endosteum near the fracture site. First, the fracture hematoma is reorganized into an actively growing connective tissue called a procallus. Fibroblasts within the procallus produce collagen fibers that help connect the broken ends of the bones. Chondroblasts in the newly growing connective tissue form a dense regular connective tissue associated with the cartilage. Eventually, the procallus becomes a fibrocartilaginous (soft) callus (kal′ŭs; hard skin). The fibrocartilaginous callus stage lasts at least 3 weeks.

Hard (bony) Callus

Third step in bone repair. Within a week after the injury, osteoprogenitor cells in areas adjacent to the fibrocartilaginous callus become osteoblasts and produce trabeculae of primary bone. The fibrocartilaginous callus is then replaced by this bone, which forms a hard (bony) callus. The trabeculae of the hard callus continue to grow and thicken for several months

Salter-Harris fracture

This is a type of break that occurs in children and involves a break in the growth plate. The type of break is indicative of the prognosis. When the break is type 1 or 2 (across the plate directly or across most of the plate and into the metaphysis) the prognosis is good. However, type 3 or 4 have a poorer prognosis (both involve the epiphysis) and type 5 has the worst (damage is caused by crushing instead of a break). In cases where the proliferative and reserve zones are interrupted, the bone will not grow properly due to premature closure of the growth plate. Fortunately, the first two types of break are the most common by far and rarely cause problems.