A 35-year-old male presents with a closed fracture of the mid-shaft humerus sustained 6 weeks ago. Clinical examination shows good callus formation and minimal tenderness. The patient is keen to know the stage of fracture healing and the best investigation to confirm the presence of bridging callus and assess fracture union.

## Investigation of Choice for Assessing Fracture Healing Stages ### Why Plain Radiography is the Gold Standard **Key Point:** Plain radiography remains the investigation of choice for assessing fracture healing and identifying the stage of callus formation (soft callus, hard callus, and remodeling phases). **High-Yield:** At 6 weeks post-fracture, bridging callus formation is expected and is best visualized on plain radiographs. The presence of bridging callus (both endosteal and periosteal) indicates progression from the soft callus stage (weeks 2–3) to the hard callus stage (weeks 3–8). ### Stages of Fracture Healing and Radiographic Findings | Stage | Timeline | Radiographic Finding | Callus Type | |-------|----------|----------------------|--------------| | Inflammatory | 0–3 days | Fracture line, soft tissue swelling | None | | Soft Callus | 2–3 weeks | Fuzzy callus around fracture site | Periosteal + endosteal | | Hard Callus | 3–8 weeks | **Bridging callus** (continuous bone bridge) | Woven bone | | Remodeling | 8 weeks–1 year | Progressive mineralization, restoration of medullary canal | Lamellar bone | **Clinical Pearl:** Bridging callus on plain radiography is the clinical and radiological sign of fracture union. It indicates that the fracture has progressed beyond the soft callus stage and can now bear load. **Mnemonic: SHBR** — Soft callus → Hard callus → Bridging → Remodeling (stages in order of appearance). ### Why Other Investigations Are Inferior - **CT scan:** Unnecessary at this stage; reserved for complex fractures, intra-articular involvement, or when plain films are inconclusive. Adds radiation without additional diagnostic benefit for simple fracture healing assessment. - **MRI:** Not the investigation of choice for fracture healing; poor visualization of cortical bone and callus mineralization. Better suited for soft tissue injury assessment. - **Ultrasound:** Operator-dependent; less reliable for assessing bony callus maturity and bridging compared to radiography. [cite:Rockwood & Green's Fractures in Adults, Ch 1]