Which skeletal site is primarily made up of cortical bone?

• A. Spine
• B. Throacic spine
• C. Distal forearm
• D. Shaft of long bones

Answer: (D)

The shaft of long bones is primarily made up of cortical bone, which is dense and forms the outer layer of the bone structure. Cortical bone, also known as compact bone, provides strength and stiffness to long bones, allowing them to support weight and resist bending and torsion. This type of bone is crucial for the structural integrity of the skeleton, particularly in load-bearing situations.

In contrast, the other options involve sites with a significant composition of trabecular or spongy bone. The spine and thoracic spine consist of vertebral bodies made primarily of trabecular bone, which is well-suited for shock absorption and energy dissipation. The distal forearm contains both cortical and trabecular bone, but the trabecular component is more pronounced in this region, especially in areas prone to fracture.

Understanding the composition and distribution of cortical versus trabecular bone is essential for evaluating bone health and assessing fracture risk in various skeletal sites. For examinations in bone densitometry, recognizing these differences in bone structure is key to proper diagnosis and treatment planning.