A 60-year-old woman presents to the physician with a 2-day history of fever and painful swelling of the left knee. She was diagnosed with rheumatoid arthritis about 15 years ago and has a 7-year history of diabetes mellitus. Over the past year, she has been admitted to the hospital twice for acute, painful swelling of the knees and hands. She is on insulin therapy and takes methotrexate, metformin, aspirin, and prednisolone 5 mg/day. Her temperature is 38.5°C (101.3°F), pulse is 86/min, respirations are 14/min, and blood pressure is 125/70 mm Hg. A finger-stick glucose test shows 230 mg/dL. Her left knee is diffusely swollen, warm, and painful on both active and passive motion. There is evidence of deformity in several small joints of the hands and feet without any acute swelling or pain. Physical examination of the lungs, abdomen, and perineum shows no abnormalities. The synovial fluid analysis shows the following: Color turbid, purulent, gray Viscosity reduced WBC 25,000/µL–250,000/µL Neutrophils > 90% Crystals may be present (presence indicates coexistence, but does not rule out infection) Which of the following is the most appropriate initial pharmacotherapy in this patient?

Intra-articular triamcinolone acetonide

A 37-year-old man presents to the emergency department after he cut his hand while working on his car. The patient has a past medical history of antisocial personality disorder and has been incarcerated multiple times. His vitals are within normal limits. Physical exam is notable for a man covered in tattoos with many bruises over his face and torso. Inspection of the patient's right hand reveals 2 deep lacerations on the dorsal aspects of the second and third metacarpophalangeal (MCP) joints. The patient is given a tetanus vaccination, and the wound is irrigated. Which of the following is appropriate management for this patient?

Surgical irrigation, debridement, and amoxicillin-clavulanic acid

Closure of the wound with sutures

Clindamycin and topical erythromycin

Ciprofloxacin and topical erythromycin

No further management necessary

Bone and joint infections for USMLE Step 2 CK: High-Yield Surgery Lessons

🦠 Pathophysiology - How Bugs Invade

Hematogenous: Via bloodstream; common in children (metaphysis) & IV drug users.
Contiguous: Spread from adjacent soft-tissue infection (e.g., diabetic foot ulcer).
Direct Inoculation: Post-traumatic, iatrogenic (surgery), or from prosthetic joints.

⭐ In children, hematogenous osteomyelitis most commonly affects the metaphysis of long bones due to its rich but slow-flowing sinusoidal vascular network.

🏰 Clinical Manifestations - Signs of Siege

Acute (Osteomyelitis/Septic Arthritis):
- Systemic: Abrupt onset of fever, chills, malaise.
- Local: Cardinal signs of inflammation: severe localized pain, erythema, warmth, swelling.
- Infants: Pseudoparalysis (refusal to move limb), irritability.
Chronic Osteomyelitis:
- Insidious, with intermittent pain and swelling.
- Sinus tract drainage is a key finding.

⭐ A draining sinus tract is pathognomonic for chronic osteomyelitis.

🔬 Diagnosis - Finding the Foe

Labs: ↑ WBC, ↑ ESR, ↑ CRP (most sensitive for tracking treatment response). Blood cultures are often drawn.
Imaging:
- X-ray: Initial test; often normal for up to 2 weeks.
- MRI: Most sensitive and specific for early diagnosis.
- CT Scan: Best for guiding biopsy and viewing bony destruction/sequestra.
Definitive Diagnosis: Bone biopsy or joint/abscess aspiration for Gram stain and culture is the gold standard.
Septic Arthritis: Synovial fluid analysis shows WBC >50,000/μL.
- 📌 Kocher Criteria: For pediatric septic hip.

⭐ MRI is the most sensitive imaging for early osteomyelitis, detecting changes within 3-5 days of onset.

⚔️ Management - Evicting the Enemy

⭐ Surgical debridement is the cornerstone of treatment for chronic osteomyelitis and septic arthritis; antibiotics alone are often insufficient.

Antibiotics: Prolonged IV therapy (4-6 weeks).
- Empiric: Nafcillin/Oxacillin (MSSA) or Vancomycin (MRSA risk).
- Definitive: Culture-directed therapy.
Surgical:
- PMMA beads: Local antibiotic delivery post-debridement.
- Amputation: Last resort for uncontrolled infection.

⚔️ Complications - Lingering Battles

Sepsis: Acute, life-threatening systemic spread.
Local Destruction:
- Pathologic Fracture: Bone weakened by infection/sequestrum.
- Joint Destruction: Cartilage loss in septic arthritis → osteoarthritis.
- Avascular Necrosis (AVN): Compromised blood supply (e.g., femoral head).
Growth & Malignancy:
- Physeal Arrest: Growth plate damage in children → limb length discrepancy.
- Chronic Sinus Tract: Draining pus to skin.

⭐ Marjolin's Ulcer: Squamous cell carcinoma (SCC) arising in a chronic, non-healing wound, classically a draining sinus tract from osteomyelitis.

$X-ray series: Chronic osteomyelitis with pathologic fracture$

⚡ Biggest Takeaways

S. aureus is the most common cause of both osteomyelitis and septic arthritis.

Key osteomyelitis associations: Salmonella in sickle cell disease, Pseudomonas in IV drug users.

Suspect N. gonorrhoeae for septic arthritis in sexually active young adults.

MRI is the most sensitive imaging for early osteomyelitis; bone biopsy is the gold standard.

Septic arthritis is an emergency. Diagnose with arthrocentesis (WBC >50,000) and treat with surgical drainage.

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Bone and joint infections