A 28-year-old woman sustains a simple fracture of the radius. At 3 weeks post-injury, histological examination of the fracture callus would show all of the following EXCEPT:

Explanation

## Histology of Fracture Callus at 3 Weeks **Key Point:** At 3 weeks post-fracture, the patient is in the **soft callus (reparative) phase**. The callus is composed of cartilage and woven bone, NOT mature lamellar bone. Lamellar bone with Haversian systems appears much later, during the remodeling phase (weeks 6–months to years). ### Timeline & Histological Findings | Timepoint | Phase | Histology | |-----------|-------|----------| | **0–2 weeks** | Inflammatory | Fibrin clot, hematoma, granulation tissue, early fibroblast infiltration | | **2–6 weeks (3 weeks = here)** | Soft Callus | **Cartilage** (hyaline and fibrocartilage), **woven bone**, fibroblasts, collagen, active angiogenesis | | **6 weeks–months** | Hard Callus | Woven bone → lamellar bone conversion, callus resorption | | **Months to years** | Remodeling | **Mature lamellar bone**, Haversian systems, restoration of normal anatomy | ### What IS Present at 3 Weeks 1. **Cartilage Matrix** - Hyaline cartilage (central, avascular region) - Fibrocartilage (peripheral regions) - Chondrocytes in lacunae actively secreting matrix 2. **Woven Bone** - Irregular, poorly organized bone trabeculae - Osteocytes embedded in bone matrix - High vascularity and cellularity - Lacks organized Haversian systems 3. **Fibroblasts & Collagen** - Type I collagen predominates - Fibroblasts active in matrix synthesis - Part of the soft tissue callus 4. **Active Angiogenesis** - New blood vessels sprouting - Supports the high metabolic demand of healing ### What IS NOT Present at 3 Weeks **Mature Lamellar Bone** - Organized concentric lamellae - Haversian systems (osteons) with central canals - Lacunar-canalicular network - **Appears only after weeks 6–12 as woven bone is remodeled** **High-Yield:** The **remodeling phase** (weeks 6 onwards) is when woven bone is progressively replaced by mature lamellar bone. At 3 weeks, lamellar bone is absent or minimal. **Mnemonic:** **WCFL** = Woven bone, Cartilage, Fibroblasts, Lacunae at 3 weeks. **NOT** Lamellar bone or Haversian systems. **Clinical Pearl:** If you see a fracture callus with mature lamellar bone and Haversian systems on histology, the fracture is at least 8–12 weeks old, not 3 weeks.