A 32-year-old male labourer presents to the orthopaedic clinic 6 weeks after sustaining a closed fracture of the mid-shaft humerus. He reports progressive pain relief and has been advised to begin active range-of-motion exercises. On examination, there is mild swelling at the fracture site and the arm is still in a sling. Plain radiographs show bridging callus across the fracture site with some endosteal and periosteal new bone formation. Which phase of fracture healing is most likely occurring at this stage?

Explanation

## Phase Identification At 6 weeks post-fracture, the patient is in the **hard callus (bony callus) formation phase**, which typically spans weeks 3–12 depending on fracture type and location. ### Timeline of Fracture Healing | Phase | Duration | Key Features | Radiographic Findings | |-------|----------|--------------|----------------------| | **Inflammatory** | 0–2 weeks | Haematoma, fibrin clot, inflammatory cell infiltration, neovascularization | Fracture line visible, minimal callus | | **Soft Callus** | 2–6 weeks | Endochondral and intramembranous ossification, cartilage formation, woven bone deposition | Bridging callus, periosteal and endosteal new bone | | **Hard Callus** | 3–12 weeks | Mineralization of cartilaginous callus, replacement by lamellar bone, increased mechanical strength | Dense bridging callus, obliteration of fracture line | | **Remodelling** | 6 weeks–2 years | Restoration of medullary canal, conversion to compact bone, removal of excess callus | Fracture line disappears, normal bone contours restored | **Key Point:** At 6 weeks, bridging callus with endosteal and periosteal new bone formation indicates transition from soft to hard callus phase. The presence of mineralized bone (not just cartilage) and clinical bridging confirms hard callus formation. **Clinical Pearl:** The soft callus phase (weeks 2–6) provides relative stability; hard callus formation (weeks 3–12) provides mechanical strength sufficient for early mobilization and weight-bearing progression. **High-Yield:** Hard callus formation is when: - Bridging callus is visible on X-ray - Fracture line begins to obliterate - Patient can tolerate active ROM and early functional loading - Mineralization of the cartilaginous template occurs **Tip:** Remember that phases overlap — soft callus begins around week 2 and hard callus begins around week 3, so at week 6, hard callus formation is the dominant process.