Final answer:
During the fibrocartilage stage of bone fracture healing, a soft callus rich in fibrous tissue is formed, which connects the broken bone ends. This callus is eventually converted into a bony callus of spongy bone, and then undergoes remodeling to create bone tissue similar to the original bone.
Step-by-step explanation:
During the fibrocartilage stage of a healing bone fracture, a soft callus rich in fibrous tissue is formed. Fibroblasts produce collagen fibers that connect the broken bone ends, while osteoblasts start to form spongy bone. This repair tissue between the broken bone ends is called the fibrocartilaginous callus. Eventually, the fibrocartilaginous callus is converted into a bony callus of spongy bone, which takes about two months for the broken bone ends to be firmly joined together after the fracture.
Additionally, the bony callus undergoes remodeling by osteoclasts and osteoblasts, where excess material on the exterior of the bone and within the medullary cavity is removed and compact bone is added to create bone tissue similar to the original bone. This remodeling process can take many months.