Osteomyelitis and Infectious Diseases

Osteomyelitis: The Basics - Bone Under Siege

• Definition: Inflammation of bone & marrow, primarily infection-driven.
• Etiology:
  • Most common: Staphylococcus aureus.
  • Neonates: Group B Strep, E. coli.
  • Sickle cell: Salmonella spp. (📌 Sickle cell - Salmonella)
  • IVDU: Pseudomonas, S. aureus.
• Routes of Infection:
  • Hematogenous: Children (long bone metaphysis), adults (vertebrae).
  • Contiguous: Trauma, surgery, ulcers.
  • Direct: Open fractures.
• Classification (Duration):
  • Acute: < 2 weeks.
  • Chronic: > 6 weeks or relapse.
• Key Pathological Features:
  • Sequestrum: Necrotic bone.
  • Involucrum: New periosteal bone.
  • Cloaca: Sinus tract.
  • Brodie's Abscess: Chronic localized abscess. ⭐ > In children, hematogenous osteomyelitis typically targets long bone metaphysis due to its unique vascularity (sluggish sinusoidal flow).

Pathogens & Pathways - Invaders & Inroads

• Key Pathogens:
  • Staphylococcus aureus: Most frequent.
  • Neonates: Grp B Strep, E. coli.
  • Sickle Cell Disease: Salmonella spp.
  • IV Drug Users (IVDU): Pseudomonas aeruginosa, S. aureus.
  • Prosthetic Joints: S. epidermidis.
  • Puncture Wounds (foot): Pseudomonas aeruginosa.
  • Vertebral (Pott's Disease): Mycobacterium tuberculosis.
• Invasion Routes:
  • Hematogenous: Children (metaphysis), adult vertebrae. Via metaphyseal capillary loops.
  • Contiguous Spread: From adjacent infections (e.g., diabetic foot ulcers).
  • Direct Implantation: Trauma, open fractures, surgery.
• Pathogenesis Unveiled:
  • Bacterial invasion → Acute inflammation, suppuration.
  • → ↑Intraosseous pressure & vascular occlusion.
  • → Ischemic necrosis → Sequestrum (avascular bone fragment).
  • → Periosteal reaction → Involucrum (new bone surrounding sequestrum). 📌 Sequestrum (dead) 'sequestered' by Involucrum (new).
  • → Chronic: Draining sinus, Brodie's abscess.

⭐ Salmonella osteomyelitis is a classic association with Sickle Cell Disease due to factors like vaso-occlusion causing bone infarcts and impaired phagocytosis.

Signs, Symptoms & Sleuthing - Cracking the Case

• Clinical Picture:
  • Acute: Fever, intense localized bone pain, warmth, swelling, ↓ limb use.
  • Chronic: Persistent dull pain, sinus tract (pus discharge), recurrent flares.
• Lab Markers:
  • ↑ WBC, ↑ ESR (often >70 mm/hr), ↑ CRP (monitors therapy).
  • Blood cultures: Positive in ~50% acute cases.
• Imaging Insights:
  • X-ray: Early changes subtle (10-14 days); later: periosteal reaction, sequestrum.
  • MRI: Gold standard for early detection; shows marrow edema, abscess.
  • CT: Details cortical destruction, sequestra.
  • Bone Scan: Sensitive, not specific.
• Definitive Diagnosis:
  • Bone biopsy (histopathology & culture) is crucial.

⭐ Sequestrum (dead bone) and Involucrum (new bone formation around sequestrum) are hallmark radiological signs of chronic osteomyelitis.

Special Forms & Fixes - Variants & Victory

• Key Variants:
  • Brodie's Abscess: Chronic, localized intraosseous abscess. X-ray: lucent nidus, sclerotic rim. Tibia common.
  • Garré's Sclerosing Osteomyelitis: Chronic, non-suppurative, prominent periosteal reaction (onion-skin). Mandible.
  • Tuberculous Osteomyelitis (Pott's Disease): Spine common. Cold abscess. Phemister's triad (osteoporosis, erosions, ↓joint space).
  • Vertebral Osteomyelitis: S. aureus common. Back pain, fever, ↑ESR/CRP.
• Core Management:
  • Surgical debridement (sequestrectomy).
  • Targeted antibiotics: IV 4-6 weeks, then prolonged oral.
  • Stabilization.
• Outcomes & Pitfalls:
  • Chronic recurrence, pathological fractures, septic arthritis.
  • Growth disturbances (children).
  • Secondary Amyloidosis (AA).

⭐ Marjolin's Ulcer: SCC in chronic sinus. Biopsy non-healing ulcers highly suspicious, especially if >10 years history of osteomyelitis drainage.

High‑Yield Points - ⚡ Biggest Takeaways

• Most common cause of osteomyelitis is Staphylococcus aureus.
• Salmonella is characteristic in sickle cell disease patients.
• Pseudomonas aeruginosa is common in IV drug users and puncture wounds through shoes.
• Tuberculous osteomyelitis (Pott's disease) typically affects the spine, causing vertebral collapse and kyphosis.
• Brodie's abscess: chronic, localized osteomyelitis, often in metaphysis.
• Sequestrum (dead bone) & involucrum (new bone) are hallmarks of chronic osteomyelitis.
• MRI is most sensitive imaging for early diagnosis of acute osteomyelitis.