Porth's Essentials of Pathophysiology, 4e

1086

Musculoskeletal Function

U N I T 1 2

U N D E R S T A N D I N G Fracture Healing A fracture, which is any break in a bone, undergoes a healing process to reestablish bone continuity and strength.The repair of simple fractures is commonly divided into four phases: (1) hematoma formation, (2) fibrocartilaginous callus formation, (3) bony callus formation, and (4) remodeling.

Hematoma Formation. When a bone breaks, blood vessels in the bone and surrounding tissues are torn and bleed into and around the fragments of the fractured bone, forming a blood clot, or hematoma. The hematoma facilitates the for- mation of the fibrin meshwork that seals off the fracture site and serves as a framework for the influx of inflammatory cells, the ingrowth of fibroblasts, and the development of new capillary buds (vessels). It is also the source of signaling molecules that initiate the cellular events that are critical to the healing process. 1 Callus Formation. As new capillaries infiltrate the hematoma at the frac- ture site, it becomes organized into a form of granulation tissue, called procallus . Fibroblasts from the peri- osteum, endosteum, and red bone marrow proliferate and invade the procallus. The fibroblasts produce a fibrocartilaginous soft callus bridge that connects the bone fragments. Although this repair tissue usually reaches its maximum girth at the end of the 2nd or 3rd week, it is not strong enough for weight bearing. 2 Fibrocartilaginous

Medullary cavity

Hematoma

Blood clot

Fibrin meshwork

Capillary buds

Compact bone

Fibrocartilaginous callus

Dead bone

Fibroblasts

New blood vessels

Collagen