Soft tissue, bone and joint infections

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  • Created by: z
  • Created on: 25-02-16 09:43

Defenses of skin and soft tissue

  • bacteria/viruses cannot penetrate intact skin
  • nonspecific defenses:
    • exfoliation- sloughing off of stratum corneum dislodges adherent bacteria
    • dryness- more infection in moist areas (groin etc)
    • acidic pH -pH 5.5 due to hydrolisis of sebum acids by skin flora
      • free fatty acids inhibit group A strep
    • low temperature
    • sweat glands- saltiness inhibits bacteria
    • normal flora- compete with pathogens for colonisation sites and nutrients
      • S. epidermidis (90% of peopole)
      • S. aureus (80% of people)
      • Micrococci
      • Diphtheroids


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Common causative agents

  • Staphylococcus aureus
    • Gram postitive cocci
    • coagulase positive
    • form distinctive  "golden colonies" on agar
  • Streptococcus pyogenes
    • AKA group A strep
    • gram positive cocci
    • beta haemolysis on agar
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Anatomical layers and related syndromes of infecti

  • Skin
    • epidermis>dermis
      • impetigo
      • folliculitis
      • furunculosis
      • carbunculosis
      • erysipelas
      • (cellulitis)
  • subcutaneous tissues
    • superficial fascia>subcut fat, nvs, art, vns>deep fascia
      • (cellulitis)
      • necrotising fascitis
  • muscle
    • myonecrosis
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Predisposing factors to skin infection

  • excessive moisture (induces breakdown of stratum corneum)
    • occlusive dressings
    • obesity-  intertriginous folds (NB intertriginous=where 2 areas of skin rub together)
  • minor abrasions
  • surgery
  • crush injuries (e.g. RTA)
  • burns
  • iatrogenic (hosiptal admission)
  • percutaneous (e.g. IV catheters)
  • bed sores
  • any condition that compromises blood supply
    • e.g. diabetics
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  • superficial infection
    • usually Staphylococcal
    • sometimes also S. pyogenes
  • friable golden crusts over erythematous skin
  • more common in children
  • highly infective
  • Rx
    • topical fucidin or mupirocin
    • oral flucloxacillin if widespread or unresponsive
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Folliculitis and other pyogenic infections

  • folliculitis
    • infection of hair follicles
      • follicle centred pustules
      • common sites:
        • scalp, groin, beard/moustache (moist areas w/ hair removal)
    • mostly (95%) S. aureus
  • furunculosis
    • deep inflammatory lesion progressing from follicultitis 
  • carbuncle
    • extends into subcut layer
    • multiple abcesses, seperated by CT
  • acute paronchia
    • skin infection arising form nail

Treatment for all: oral flucloxacillin

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  • acute, spreading infection of lower dermis and associated subcut layers
  • diffuse inflammation without necrosis or localisation of pus "red halo"
    • skin is hot, red and painful
  • causative organisms:
    • commonly S. aureus (CA-MRSA= community associated MRSA - NB less resistant)
    • less commonly S. pyogenes, C. perfringens
  • most commonly affects lower extremities
  • diagnosis
    • acute, tender, eythematous, swollen area of skin
    • fever and malaise
    • WCC and CRP
    • NB blood cultures not useful unless pt septic
  • treatment
    • rest and elevation, mark area of cellultits
    • oral penicilllin V & flucloxacillin (IV if severe)
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  • well demarcated cellulitis with fever and malaise
  • lesions raised above surrounding skin + clear line of demarcation
    • diagnosis through clinical appearance
  • S. pyogenes most common cause
  • legs or face most common sites
  • treatment: penicillin
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Staphylococcal scalded skin syndrome (SSSS)

  • infants, young children and the immunocompromised
  • mediated by production of exfoliative toxins A or B carried by ~3% S. aureus
    • released into blood stream from localised infection
  • causes widespread superficial exfoliation
  • treatment: flucloxacillin
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Necrotising fasciitis

  • caused by either single (eg Gp A) or multiple organisms
  • bacteria enter fascial plane (via trauma/surgery/occult bacteraemia) and spread rapidly
    • inflammatory response- vessel thrombosis- compromises blood supply and nerves to skin
      • skin over infected area: red/dusky red/grey and painless
  • 3 stages of symptoms
    • early (<24hr)
      • presence of skin trauma w/ pain disproportionate to injury
      • flu like symptoms and thirst
    • advanced
      • swelling of painful area
      • large violet blotches
      • mottled, flaky appearance at trauma site
    • critical symptoms
      • toxic shock, severe fall in BP, unconsciousness
  • Treatment: IV antibiotics and surgery
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Gas gangrene

  • Clostridium perfringens is most common cause
  • common in past wars with devitalised wounds contaminated by soil
  • can occur in synergistic infections
    • e.g. wound infected by coliforms which use up oxygen crfeating conditions for anaerobes
  • more common in pt w/ underlying blood vessel disease, DM or colon ca
  • treatment: urgenct surgery to remove dead tissue
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Surgical site infection (SSI)

  • "infections that affect the surgical wound or deeper tissues handled during the procedure resulting in local signs and clinical symtpoms" (within 30 days of surgery or 1 year if implant)
    • classified as incisional or organ/space infection
  • up to 20% of all healthcare associated infectioins- 5% of all surgeries
  • typical features of SSI:
    • incr exudate/swelling/erythema/pain/local temp,
    • change in granulation tissue- discolouration, prone to bleed, highly friable
  • factors that impact on SSI
    • pt- extremes of age, poor nutritional state, obesity, immunocompromised,smoking
    • procedural- scrub, pre-op shaving & skin prep, skin anti-sepsis, length of op, thearte ventilation, instrument sterilisation, foreign material in surgical site
    • microbial- level of contamination
  • prevention
    • pre-op: patient prep, hair removal, antibiotic prophylaxis, staff prep
    • intra-op: team prep, pt skin prep, pt homeostasis, wound dressings
    • post-op: dressing and wound cleaning, ab Rx, debridement, wound care services
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Septic arthritis

  • infection of joint space
  • S. aureus, Streptococci, Gram negatives
  • esp if Hx of RA or trauma
  • routes of bacterial entry:
    • haematogenous (most important)
    • direct inoculation via trauma
    • arthritis with assoc tendonitis
  • bacteria enter joint space>inflammatory response>neutrophil invasion
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Acute osteomyelitis

  • S. aureus, H. influenzae, E. coli, P. aeruginosa, Proteus mirabilis
    • via direct inoculation (trauma/surgery) or haematogenous route
  • pathology
    • bacteria in metaphysis results in: oedema, incr vascularity, influx polymononuclear L
    • blood supply to area decr: necrosis of infected bone- formation of sequestrium
    • residual dead bone acts as foreign body- hard to eradicate bacteria (chronic progresion)
  • acute clinical features:
    • adults- severe pain, decr mvmt, fever/malaise, backache, history of UTI or uro surg
    • infant- failure to thrive, drowsy, irritable, metaphyseal tenderness, decr ROM
  • acute osteomyelitis diagnosis:
    • Hx and exam
    • FBC, ESR, blood culture,aspiration (NB risk of introducing more infection)
    • XR (normal in first 10-14 days), USS, bone scan, MRI
  • treatment: flucloxacillin (clindamycin if allergic) or vancomycin if MRSA (+ fusidic acid, linezolid or rifampicin if prothesis present or life threatening condition) for 4-6/12 wk (ac/chr)
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Diabetic foot infections

  • cellultis > deep soft tissue infection > osteomyelitis
  • organisms
    • skin organisms: S. aureus, Gp A strep, diphtheroids
    • gram -ve bacilli: E. coli, K. pneumoniae, Pseudomonos spp
    • anaerobes
  • RFs
    • vascualr disease
    • peripheral neuropathy
    • poor foot care
  • Treatment:
    • mild
      • flucloxacillin (if MRSA- doxacycline/if pen allergy- clindamycin)
    • moderate
      • co-amoxiclav (if MRSA- add vancomycin/pen allergy- clindamycin)
    • severe
      • Tazosin (add vancomycin if MRSA/pen allergy- meropenem)
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Viruses and dermatophyte infections

  • viruses
    • HSV and VZV produce vesicular lesions
      • HSV normally only gentital/oral regions
      • both can persist in DRG- can reactive w/ dermatomal distribution
    • other V have characteristic skin rashes
      • rubella, measles, parvovirus, HSV6
  • dermatophyte infcetion (ringworm)
    • fungi that invade dead tissues or its appendages (nails/hair)
    • most common are Trichophton, Epidermophyton, MIcrosporum
      • hard to distinguish clinically
    • spread person-person or animal-person
    • diagnosis clinically acording to site:
      • tinea pedis (athletes foot)
      • tinea barbae (Barbers itch)
    • treatment: topical imidazoles/oral triazone if resistant or widespread
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