Final answer:
The fifth step in the fracture healing process is the remodeling phase, where osteoclasts and osteoblasts collaborate to refine the bone structure and improve the bone's strength to its pre-injury state.
Step-by-step explanation:
The fifth step in the fracture healing process is remodeling. Bone remodeling is a vital phase where the healed bone undergoes further transformation to refine its structure and improve its strength. Initially, after a bone fracture, a series of steps occurs: (a) formation of a fracture hematoma, (b) formation of internal and external calli, and (c) replacement of cartilage by trabecular bone. Once the bony callus has formed, remodeling begins. During this phase, osteoclasts and osteoblasts work together to remodel the callus into mature bone. Excess material on the exterior and within the medullary cavity is removed, while compact bone is laid down to restore the bone to its original shape. Over time, the bone adapts and becomes stronger to handle the stresses it encounters.
It is essential to recognize that this final phase may take several months and the bone's surface might remain slightly uneven for years, although often the region undergoes enough remodeling that no external evidence of the fracture remains.