Which description matches fast-growing endosteal bone formation?

• A. Woven bone deposited perpendicular to trabecular surfaces, forming a web in intertrabecular space
• B. Lamellar bone deposited on preexisting surfaces
• C. Periosteal reaction along cortex
• D. Cartilage formation within the marrow

Answer: (A)

Rapid endosteal bone formation is typically composed of woven bone laid down quickly on inner bone surfaces. Woven bone has disorganized, randomly oriented collagen fibers and forms a dense, web-like network. When this occurs in trabecular bone, the new bone tends to be deposited perpendicular to existing surfaces, filling the intertrabecular spaces as a mesh. This rapid, scaffolding-like bone is then usually remodeled over time into the more organized lamellar bone.

In contrast, lamellar bone is laid down in orderly, parallel layers on preexisting surfaces and represents slower, mature remodeling. A periosteal reaction occurs on the outer bone surface along the cortex, not endosteally. Cartilage formation within the marrow points to endochondral ossification, where a cartilage template is replaced by bone rather than direct endosteal deposition of bone tissue.

So the description of woven bone forming a web in intertrabecular space on endosteal surfaces aligns with fast-growing endosteal bone formation.