Which is the key feature of fracture callus outside-to-inside maturation?

• A. Presence of numerous mitoses
• B. Uniform woven bone throughout
• C. The zonal maturation sequence outside-to-inside replacement of cartilage by woven bone
• D. Lack of cartilaginous replacement

Answer: (C)

Fracture healing shows a distinct zonal maturation from the outer edges toward the center, with cartilage and other soft tissue at the periphery being progressively replaced by woven bone as healing proceeds inward. This outside-to-inside pattern reflects endochondral ossification forming a hard callus from the outside in. The periphery converts cartilage to woven bone first, while the center lags behind, creating a characteristic gradient of tissue maturation.

This is the best description because it directly captures the spatial-temporal sequence that defines how the callus matures. While mitotic activity can occur, it isn’t the defining feature of this pattern. The callus is not uniformly woven bone throughout during maturation, and cartilaginous replacement is a key part of the process, not something to be missing.