Why is the diaphysis often the site of fractures?

• A. It has a poor blood supply and joint involvement
• B. It has a good blood supply and no joint involvement
• C. It is near a growth plate
• D. It contains mainly red marrow

Answer: (B)

Fracture location is influenced by how bone is stressed and how it heals. The diaphysis, the shaft of a long bone, bears a lot of bending and twisting forces, so midshaft breaks are common. Healing is efficient there because the cortical bone of the diaphysis has a robust blood supply from periosteal vessels and the nutrient artery, which supports rapid callus formation and repair. Being away from joints, a fracture in the diaphysis usually does not involve a joint surface, reducing the risk of intra-articular damage. That combination of good vascular support and no joint involvement makes diaphyseal fractures common and tends to heal well. The other options don’t fit: the diaphysis isn’t characterized by poor blood supply or joint involvement, in adults it mainly contains yellow marrow rather than red, and growth plates are located near the ends of long bones (metaphysis) in children, not in the diaphysis.