L05 I&I Infections of Bones and Joints (changed 28_2)

Infections of Bones and Joints (changed 28/2)

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Status: S1LectNotes Time: 2025-04-02 Tags: lecturenotes InfAndImm Links:

tasks:

Content:

Summary/things to note:

Objectives:

Learn the:

• Aetiology and risks of:
  • Osteomyelitis
  • Septic arthritis
• Laboratory diagnosis of bone and joint infections
• Treatment of bone and joint infections

Objective based questioning:

Content:

Osteomyelitis

infection of bone basically

• Inflammatory process of bone secondary to infection
  • may involve periosteum. medullary cavity, compact, cancellous bone
• methods of classification
  • Duration
    • Acute
    • Subacute
    • Chronic
  • Route of infection
    • Haematogenous (most common is children due to slow blood flow in the epiphyseal cartilage plate)
    • Exogenous
      • direct (injury)
      • contigous → spread from a local infectio
        • common in diabetics
      • polymicrobial
  • host response
    • Pyogenic
    • Granulomatous little balls of marcophags surrounding the bacteria

aetiology

Species of pathogens Staph aureus → 90% infection in children 30-50 infections adults

1. Haematogenous (Monomicrobial)
   1. Neonates (Premature)
      1. S aureus S agalactae, Ecoli
   2. Children 2. S. aureus S pyogenes, S pneumoniae, E coli
   3. Adults
      1. S aureus, streps/ enterococci, Gram negative
2. Exogenous (often polymicrobial) 4. s aureus 90% infection in children 50% in adults 5. streps/enterococci 6. gramnegatives 7. obligate anaerobe

Risk factors for osteomyelitis:

1. immunosuppression
2. age
3. PVD
4. IDu
5. chronic joint disease
6. recent bone surgery/jiont replacement/ bone trauma
7. lack of spleen (spleen removes opsonised bacteria) liver removes unopsonised bacteria
8. less bloodflow into limbs

clinical presentation

• children
  • metaphysis of long bones
  • sever pain oedema erthema
  • pseudoparalysis
  • fever malaside nausea vomiting
  • lass dramatic in infants
• adults
  • haematogenous
    • onser less acute
    • can present as backache when in that area
  • contiguous
    • diabetics (feet)

complication

Pathogenesis

• inflammation
  • increased pressure in bone
  • ischemia and necrosis
  • osteolysis
• suppuration
  • pus formation in bone
    • sinus formation in chronic infection
• sequestrum
  • dead bone
• involucurm
  • covers dead bone (new bone)
• resolustion or progression to complication

diagnosis

• get pus from the bone
  • try not to get pus from skin
• gram stain
• culture
• try to identify the bacteria before prescribing but sometimes empiric therapy is needed
• haematogenous osteomyelitis can do blood culture
• slinical diagnosis important
• leukocytosis
• raised CRP
• Imaging can help

  • 50% bone loss needs to occur to be seen

  • need illness to be present for >1week
• boncescans with radioisotopes

treatment

• medical
  • Iv empiric broadspectrum or combinations
    • S aureus streptococci pseudomonas ecoli
      • flucloxacillin vancomycin (saureus/MRSA/Sepidermis)
      • penicillin (streps)
      • cephalosporin/fluoroquinolones (ecoli)
      • B lactam Blactamase inhibitor / folouroquinolone/carbepenem (pseudomonas)
  • change to narrow spectrum when more precision is possible
  • prolonged antimicrobial therapy 4-6 iv 2-4 wk oral
• surgical
  • debridement
    • not really needead in kids
  • amputation

subacute osteomyelitis

• brodies abcess (localised abcess (s Aureus))
• few clinical signs
• diagnosis
• treatment
• surgical debrinement

chronic osteomyelitis

• complication of AOM
  • sequestrum can become an infectious reseviour
  • can arise denovo
  • postsurgical trauma diabetes
  • oftenpolymicrobial
  • grandulatomuous
• diagnosis
  • biopsy → culture and staining
  • imagins
    • xray
• treatment
  • surgical debridement
    • sequestectomy
  • long course antimicrobial

Septic arthritis invasion of the joint by a pathogen which produces arthritis

• Bacteria (more serious)
• viruses
• fungi

can be acute or chronic

• Focus of acute bacterial
  • most damagine and serous

disease is characterised by

• colonistion of the synovial fluid

• influx of inflammatory and immune cells

• effusion into joint space

• erosion of synovial membrane

• 60-80% s aureus

• s epidermisidis common in prosthetic joint replacements

• neisseria gonorrhoeae → following STI

  • 75% of cases in younger sexually active people

• gram negatives

  • immunocompromised people

• sometimes but not often polymicrobials anaerobes

  • found in trauma and metastatic infection

increasing incidence due to higher joint replacements clinical entity

• <3 mths post implant (early onset)
  • S. aureas probably originated probably from surgery (biofilm)
• 3-24 months post implant (late onset)
  • S epidermidis → biofilm
  • both aureus and epidermidis make biofilms on artificial joints and attach to layer of platelets and fibrin lain on the joint replacement by body

• 24 months

  • haematogenous spread risk factors
• damaged joints (OA, RA, GOUT)
• immunosuppression
• joint replacement
• age ~50% 0ver 65
• IDU clinical symptoms
• acute onset of inflammation swelling → joint effusion
  • loss of mobility → pseudoparalysis
• arthralgia
  • knee 40-50% (most common site in adults)
  • hip 20-25% (most common site in children)
  • ankle, shoulder, wrist, elbow fingers 10-15%
• monoarticular (polyarticular likely aureus or neisseria)
• few systemic signs
  • low grade fever

routes of entry

• direct inoculation
• infection of periarticular tissues
• haematogenous spread complications
• sepsis
• osteomyelitis
• joint destruction diagnosis
• aspiration of synovial fluid
  • turbid, yellow dicreased viscosity indicative of infection
• gram stain
  • direct empiric antimicrobial
• culture
  • non neisseria cases positive unless Ax
• blood culture
  • ~50% s Aureus cases positive
• imaging stidues
  • xray ultrasound

treatment

• rapid treatment required
• medical
  • iv empirical therapy
  • s aureua
    • flucloxacillin
  • MRSA
    • vancomysin
  • neisseria gonorrhoeae
    • cephalosporin
  • 2-4 wks iv 1-2 oral
• surgical
  • apiration/drainage
  • removal of prosthesis or debridement