Which skeletal site is mostly composed of cortical bone?

• A. Proximal forearm
• B. Lumbar spine
• C. Hip
• D. Calcaneus

Answer: (A)

The proximal forearm is primarily composed of cortical bone, which is dense and forms the outer layer of bones. Cortical bone makes up about 80% of the total bone mass in the human skeleton, providing strength and rigidity. The structure of the proximal forearm, which includes the distal ends of the radius and ulna, signifies the predominant presence of cortical bone, suited for bearing loads and resisting bending.

In contrast, the lumbar spine and the hip contain a significant amount of trabecular or cancellous bone, which is found within the inner regions of bones and is responsible for the storage of marrow and minerals as well as energy metabolism. Trabecular bone has a higher surface area relative to its volume, allowing for quick remodeling but is less dense than cortical bone. The calcaneus, or heel bone, also has a substantial trabecular component, designed to absorb shock and support weight while providing stability in movement.

Thus, when identifying a skeletal site predominantly composed of cortical bone, the proximal forearm is the correct choice due to its structural characteristics and functional role in supporting mechanical loads.