Weakest part of a normal bone is along what?

• A. Diaphysis
• B. Epiphysis
• C. Metaphysis
• D. Periosteum

Answer: (A)

The main idea here is where a long bone tends to fail first under typical loads: the midshaft region, or the diaphysis, is the weakest link. The diaphysis is a hollow cylinder of dense cortical bone that carries the bulk of bending and torsional stresses along the bone’s length. When forces are applied, this central shaft bears high moments of bending with relatively less reinforcement from the ends, which are shaped by articular surfaces and a different internal architecture. The ends (epiphyses) are protected by articular cartilage and have more cancellated bone that helps distribute stress, while the metaphysis sits at a transition with a different lattice structure. The periosteum, while important for growth and repair, isn’t a primary contributor to structural strength. For these reasons, the diaphysis is typically considered the weakest part of a normal bone.