Final answer:
The healing process of a fractured bone involves the formation of a fibrocartilaginous callus by osteoblasts and fibroblasts, which is replaced by trabecular bone through endochondral ossification, forming a bony callus. This callus is then remodeled over months to restore the bone to its original form.
Step-by-step explanation:
When a bone is fractured, the healing process involves the formation and replacement of a callus. Initial bleeding at the fracture site forms a hematoma, which is a clot that serves to seal severed blood vessels. Soon after, capillaries grow into the hematoma and phagocytes begin to remove dead cells. Fibroblasts produce collagen fibers that bridge the broken bone pieces, and osteoblasts generate spongy bone, creating a structure known as the fibrocartilaginous callus.
The internal fibrocartilaginous callus is a matrix that provides the framework for new trabecular bone. Osteoclasts resorb dead bone while osteogenic cells become active and differentiate into osteoblasts, which replace the callus with new bone through a process called endochondral ossification. This newly formed trabecular bone then gets remodelled into a bony callus.
The bony callus is reshaped by osteoclasts and osteoblasts, removing excess material from the bone exterior and medullary cavity, eventually forming compact bone. This bone remodeling process can extend over several months, with the bone's surface potentially staying uneven for years, but eventually leading to a structure remarkably similar to the original bone before the break.