Which of the following is NOT a trigger for reactive bone formation?

• A. Physical elevation of the periosteum from a tumor or inflammatory exudate
• B. Mechanical weakness (compensatory new bone formation)
• C. Fracture
• D. Nutritional deficiency causing osteolysis

Answer: (D)

Reactive bone formation happens when the periosteum is irritated or stress is placed on the bone, prompting osteoblasts to lay down new cortical bone along the outer surfaces. This periosteal response is seen when the periosteum is elevated or irritated by a subperiosteal mass or inflammatory exudate, creating a new bone layer as a protective or adaptive reaction. It also occurs with fracture, where the healing process involves new bone formation (callus) to bridge and stabilize the injured area, and with mechanical weakness that prompts compensatory reinforcement of the affected region.

In contrast, a nutritional deficiency that causes osteolysis leads to bone loss rather than a periosteal reaction. Osteolysis weakens bone structure through resorption, not by stimulating new bone formation on the periosteal surface. Therefore, the nutritional deficiency causing osteolysis is not a trigger for reactive bone formation.