Which of the following is the most characteristic radiological finding in the early stage (first 7–10 days) of acute hematogenous osteomyelitis?

Explanation

## Radiological Findings in Acute Hematogenous Osteomyelitis: Timeline and Progression **Key Point:** In the early stage of acute osteomyelitis (first 7–10 days), plain radiographs are often **normal or show only soft tissue changes**; bone changes appear later as the infection progresses. ### Radiological Timeline | Stage | Time Frame | Plain Radiograph Findings | Advanced Imaging (MRI/CT) | |-------|-----------|---------------------------|---------------------------| | **Early/Acute** | 0–7 days | Soft tissue swelling, obliteration of tissue planes, loss of fat planes | Bone marrow edema, hyperintense T2 signal, early intramedullary involvement | | **Early subacute** | 7–14 days | Periosteal reaction begins, subtle metaphyseal lucency may appear | Abscess formation, cortical involvement | | **Established** | 2–4 weeks | Cortical thickening, periosteal new bone formation, metaphyseal lucency | Sequestrum (dead bone), involucrum (new bone shell) | | **Chronic** | >4 weeks | Sequestrum, involucrum, sinus tract, pathological fracture | Chronic abscess, cloaca, fistula tract | **High-Yield:** **Soft tissue swelling and obliteration of normal tissue planes** is the earliest and most consistent radiological sign in the first 7–10 days. This occurs because the infection spreads through the Haversian and Volkmann canals into the medullary cavity and then breaks through the cortex into the periosteum and surrounding soft tissues. ### Why Other Findings Appear Later **Cortical thickening and periosteal new bone formation** (option A): - Requires 10–14 days or more to become visible on plain radiographs - Represents the body's attempt to wall off the infection - Appears as a "sunburst" or "onion-skin" pattern **Pathological fracture** (option C): - Occurs only in advanced, destructive disease - Indicates significant cortical compromise - Not seen in early-stage acute osteomyelitis **Sequestrum and involucrum** (option D): - These are hallmarks of **chronic osteomyelitis** - Sequestrum = dead bone that has been separated from living bone - Involucrum = new bone shell formed around the sequestrum - Requires weeks to months to develop **Clinical Pearl:** MRI is far superior to plain radiographs in early osteomyelitis, showing bone marrow edema and intramedullary involvement within 24–48 hours, even before plain radiographs become abnormal. However, the question specifically asks about radiological findings in the early stage, and soft tissue changes are the earliest plain radiograph abnormality. **Mnemonic:** **SOFT FIRST** — In early acute osteomyelitis, **S**oft tissue swelling comes **F**irst, **I**nflammation spreads before **R**adiographic bone changes appear, **S**equestrum and involucrum come **T** later (chronic stage). [cite:Rockwood & Green's Fractures in Adults Ch 15]