A 34-year-old male construction worker from Delhi presents with a 3-week history of progressive pain and swelling over the right tibia. He recalls a puncture wound to the sole of his foot 6 weeks ago while working barefoot on a construction site. On examination, the right foot shows a small, painless scar on the plantar surface; the tibia is warm, tender, and swollen. X-ray of the tibia shows a mixed lytic and sclerotic lesion in the diaphysis with periosteal reaction. Blood culture and bone culture both grow Pseudomonas aeruginosa. What is the most likely diagnosis and the primary reason for this organism's involvement?

Explanation

## Clinical Diagnosis: Contiguous Osteomyelitis ### Key Features of This Case **Key Point:** The puncture wound to the plantar foot 6 weeks prior is the source of infection. Pseudomonas aeruginosa is the classic organism associated with puncture wounds, particularly those contaminated with soil or water. **High-Yield:** Puncture wounds to the foot (especially through rubber-soled shoes) are notorious for introducing Pseudomonas into deep tissues. The organism thrives in moist environments and can track along tissue planes to reach bone. ### Osteomyelitis Classification & Pathogenesis This case represents **contiguous osteomyelitis** (also called osteomyelitis secondary to soft tissue infection), not haematogenous spread. The infection originated from the puncture wound and spread locally to the tibia. ### Why Pseudomonas aeruginosa? | Feature | Pseudomonas aeruginosa | |---------|------------------------| | **Source** | Soil, water, moist environments | | **Common portal** | Puncture wounds, especially plantar foot | | **Virulence factor** | Produces exotoxins, biofilms; thrives in anaerobic environments | | **Bone tropism** | Not inherent; reaches bone via direct inoculation or contiguous spread | | **Antibiotic resistance** | Intrinsic resistance to many β-lactams; requires fluoroquinolones or anti-pseudomonal agents | **Clinical Pearl:** A plantar puncture wound with a small, often-overlooked scar is the classic presentation. The patient may not recall or report the injury if it was minor and painless initially. ### Diagnostic Confirmation 1. **Positive blood culture + bone culture** = confirms osteomyelitis (not just soft tissue infection) 2. **Imaging findings** (mixed lytic/sclerotic, periosteal reaction) = consistent with acute-to-subacute osteomyelitis 3. **Organism identification** (Pseudomonas) = confirms puncture wound source **Mnemonic: FOOT PUNCTURE PSEUDOMONAS** — Foot puncture wounds → Pseudomonas → Contiguous osteomyelitis ### Management Implications - **Antibiotic choice:** Fluoroquinolones (ciprofloxacin) or anti-pseudomonal penicillins (piperacillin-tazobactam) + aminoglycosides - **Duration:** 4–6 weeks IV, then oral step-down - **Surgical debridement:** May be needed if abscess or sequestrum present [cite:Rockwood & Green's Fractures in Adults Ch 37]