Which histologic feature supports fracture callus diagnosis?

• A. The zonal maturation sequence outside-to-inside replacement of cartilage by woven bone
• B. High cellular pleomorphism
• C. Numerous mitoses
• D. Uniform cartilage only

Answer: (A)

Fracture healing shows endochondral ossification with a distinct zonal pattern. In the healing callus, cartilage forms and is arranged in an outside layer that is progressively replaced by woven bone toward the center as the fracture is bridged. This outside-to-inside maturation sequence—cartilage transitioning to bone—is a hallmark of fracture callus and reflects the staged repair process. In contrast, features like high cellular pleomorphism or numerous mitoses suggest neoplastic or other aggressive processes, not normal repair, and uniform cartilage alone does not capture the progressive ossification seen in a true fracture callus.