In bone biology, growth on the outer surface that increases bone diameter is called?

• A. Endochondral ossification
• B. Osteogenesis
• C. Intramembranous ossification
• D. Appositional growth (bone remodeling)

Answer: (D)

Appositional growth is the process that increases bone diameter. It happens when osteoblasts in the periosteum lay down new bone on the outer surface, making the bone grow wider. Meanwhile, bone is often resorbed from the inner surfaces to keep the overall structure balanced, which is why the bone can thicken without just piling on inside. This widening by adding bone to the outside is what defines appositional growth. The other terms describe different bone-forming processes: lengthening via replacing cartilage with bone (endochondral ossification), forming bone directly from connective tissue (intramembranous ossification), or the general process of bone formation (osteogenesis).