Which site is NOT commonly associated with trabecular bone?

• A. Proximal femur
• B. End of long bones
• C. Cortical shaft
• D. Areas of low mechanical stress

Answer: (C)

Trabecular bone, also known as cancellous or spongy bone, is characterized by a porous structure that is typically found in areas of the skeleton where there is less mechanical stress and where bone can act more as a supportive framework. The proximal femur and the ends of long bones are well-known sites rich in trabecular bone, as they require the ability to absorb shocks and provide support to the joints.

The cortical shaft, in contrast, is primarily composed of cortical bone, which is dense and provides strength and structural support. Cortical bone is typically found in the outer layer of bones and is less porous than trabecular bone. It is associated with areas that withstand high mechanical loads due to its rigidity. This distinction makes the cortical shaft the correct answer since it is not a site commonly associated with trabecular bone. The other locations mentioned are all characterized by significant trabecular bone presence, highlighting the need to understand the structural distinctions and functions of bone types when considering bone density assessments.