Bone and Joint Infections

Osteomyelitis - Bone's Fiery Foe

Bone inflammation, typically infectious.

• Classification by Route:

  • Hematogenous (blood-borne)
  • Contiguous focus (spread from adjacent infection)
  • Direct inoculation (trauma, surgery)

• Common Pathogens:

  • Staphylococcus aureus: Most common overall.
  • Neonates: Group B Strep (GBS), E. coli.
  • IVDU, Puncture wounds (e.g., foot): Pseudomonas aeruginosa.

  • ⭐ In sickle cell disease, Salmonella species are a characteristic cause.

• Types:

  Feature	Acute Osteomyelitis	Chronic Osteomyelitis
  Onset	Sudden, < 2 weeks	Insidious, > 2 weeks
  Symptoms	Fever, intense pain, local inflammation	Draining sinus, recurrent pain, deformity
  X-ray (early)	Soft tissue swelling; normal bone	Sclerosis, sequestrum, involucrum
  Pathology	Acute inflammation, bone necrosis	Dead bone (sequestrum), new bone (involucrum)

• Diagnosis & Management:
  • Antibiotics: Typically 4-6 weeks IV; may be followed by oral.
  • Surgical debridement often for chronic cases/abscess.

Septic Arthritis - Joint Under Siege

Bacterial invasion of synovial joint space. A medical emergency requiring prompt diagnosis and treatment.

• Pathogens by Age Group:
  • Neonates: GBS, S. aureus, Gram-negative bacilli.
  • Children <5y: S. aureus, S. pyogenes.
  • Older children/Adults: S. aureus.
  • Sexually active: N. gonorrhoeae.
  • IVDU: Pseudomonas aeruginosa, S. aureus.
• Synovial Fluid Analysis: WBC >50,000/mm³ (often >100,000), PMNs >75%, ↓Glucose, Gram stain (+ in ~50-70%), Culture (+ in ~70-90%).
• 📌 Kocher's Criteria (Pediatric Septic Hip):
  • Fever >38.5°C
  • Non-weight bearing
  • ESR >40 mm/hr
  • WBC >12,000/mm³ (≥3 criteria suggest high probability)

⭐ Kocher criteria are highly useful for differentiating septic arthritis from transient synovitis in children with an irritable hip.

Prosthetic Joint Infections - Implant Invasion

• Infection involving a joint prosthesis and adjacent tissues; biofilm formation on implant is key.
• Classification by Onset & Common Pathogens:

⭐ Biofilm formation by bacteria like Staphylococcus epidermidis is a major challenge in prosthetic joint infections, often necessitating implant removal.

Specific Bone/Joint Infections - Unique Bone Invaders

• Tuberculous Spondylitis (Pott's Disease)
  • Site: Thoracolumbar spine.
  • Features: 'Cold abscess', psoas abscess, gibbus deformity.
  • Paradoxical reaction. ATT: 9-12 months.
  • 
• Brucellar Spondylitis
  • Key: Sacroiliitis.
  • Signs: 'Pedro Pons' sign' (vertebral erosion), undulant fever.
  • 
• Fungal Osteomyelitis
  • Agents: Candida, Aspergillus.
  • Risks: Immunocompromised, IVDU, TPN.

⭐ > Pott's disease (tuberculous spondylitis) most commonly affects the lower thoracic and upper lumbar vertebrae, and can lead to characteristic 'cold abscesses' and kyphotic deformity (gibbus).

High‑Yield Points - ⚡ Biggest Takeaways

• Staphylococcus aureus is the most common cause of osteomyelitis and septic arthritis.
• In neonates, consider Group B Streptococcus and E. coli.
• Salmonella is characteristic in sickle cell disease patients with osteomyelitis.
• Pseudomonas aeruginosa is common in puncture wounds and IV drug users.
• Kingella kingae is a key pathogen for septic arthritis in children < 4 years.
• Mycobacterium tuberculosis can cause Pott's disease (vertebral osteomyelitis).
• Brucellosis often involves the sacroiliac joints and spine (spondylitis).