Osteoporosis is characterized by bone resorption outpacing deposition, with vertebral and hip fractures common; which part of bone is most susceptible?

• A. Spongy bone of spine and neck of femur
• B. Cortical bone of skull
• C. Compact bone of tibia
• D. Dense bone of the pelvis

Answer: (A)

The part of bone most affected is the spongy (trabecular) bone found in areas with high metabolic activity, especially the vertebral bodies and the neck of the femur. Spongy bone has a large surface area and a rapid remodeling rate, so when osteoporosis causes bone resorption to outpace deposition, the trabecular network thins and holes form quickly. This weakens the internal support where most of the load is transmitted and makes the spine prone to compression fractures and the hip region prone to fractures. In contrast, cortical bone (the dense outer layer) remodels more slowly and is less immediately affected, which is why the spine and hip are classic sites of osteoporotic fractures while other dense bones like the skull or pelvis are less commonly involved.