Sunday, November 19, 2017

The ABR Core Study Guide MSK - Soft Tissue Infection Notes

Soft Tissue Infection


  1. Etiology - many ways - inhalation, ingestion, direct inoculation, hematogenous, lymphatic, direct invasion
  2. Factors that increase risk of infection - host immune system, poor vascular supply, necrotic tissue, tissue injury, collections of blood or lymph, implanted devices, foreign bodies
  3. Tumors can become secondarily infected
  4. Systemic disorders or immune suppression may alter how infection presents
  5. Staphylococcus Aureus - most common etiology of soft tissue infection; Streptococcus A is number 2
  6. Some occupations predispose to certain infections - rice field workers and meliodosis; tropical fish enthusiasts - mycobacterium marinum
  7. Presentation dictated by type of infection
  8. Typical - early is erythematous, warm, increased blood flood and dilated capillaries - complain of pain, swelling an heat; Febrile; subsequently may have tissue destruction and necrosis; septic shock - hypotension, tachycardia
  9. Slow growth infections - local destruction and abscess formation; microcavities to larger cavities; may invade adjacent structures; sinus track to skin
  10. Invade joint - can cause early irreversible articular damage; low blood supply to joint naturally
  11. Chronic infections - stable or steady state; chronic reactive changes and acute infection changes; fibrous tissue adjacent an abscess; develop cloacae or sinus tracks lined by epithelium
  12. Chronic - may eventually have amyloid development or malignant transformation.
  13. X-ray - limited - may show nothing; may show soft tissue edema or secondary effects such as mass effect on adjacent structures, periosteal reaction in adjacent bone or bone changes from an adjacent abscess
  14. Ultrasound useful for abscess versus cellulitis.
  15. MRI - find abscesses, determine sinus tracks, determine involvement of adjacent bone
  16. Cellulitis - superficial; can involve tendons
  17. Abscesses - many sources - s. aureus, bowel flora etc; if sinus tracks can cause further spread and can be associated with Squamous Cell Carcinoma in long term skin infections
  18. Acute septic arthritis - in kids most are not infectious but transient synovitis - but they look the same - so aspirate; if transient - it will help pain; If infection - will help find source
  19. Acute septic arthritis - Adults - Diff Dx - acute arthropathy, gout, pseudogout, polyarthropathy and systemic arthropathies. Strep pyogenes, staph aureus, N. gonorrhea, Beta-hemolytic strep
  20. Chronic Septic Arthritis - Organism must be determined; prosthesis - often skin contaminates; 
  21. Pyomyositis - fever, pain with passive motion; elevated markers; A muscle or other muscles; gas gangrene is severe and often fatal; often fluid collections; staphylococcus and clostridial myonecrosis
  22. Necrotizing fasciitis - group A strep or polymicrobacterial; gas is possible; fascia will be thickened; muscles and muscle groups will have abnormal signal
  23. Tuberculosis - 3rd most common infection worldwide - "cold" abscess - may not have a pyrexial component; when invading bone can look like a malignancy; mycobacterium marinum - nodular lymphadenitis
  24. Fungal - often immunocompromised; variable presentation 
  25. Ultrasound - useful for determining if fluid collection or just soft tissue edema
  26. MRI - definitive study for both dx and progression
Reference: Thomas Pope et al Expert Consult Musculoskeletal Imaging 2nd Edition

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