Septic Arthritis

Definition

  • Joint inflammation due to infection by micro-organisms

Incidence

  • All age groups
  • Usually children
  • 50% < age 3
  • M=F
  • Any joint
  • Knee is most common joint affected overall
    • Infants
      • Hip
    • Children
      • Knee
    • Adults
      • Large Joints
    • IVDU
      • SCJ & SIJ

Pathogenesis

  • Two Routes
    • Haematogenous
      • Distant focus
      • Seeds synovial membrane
    • Direct
      • Extension
        • Osteomyelitis
          • Neonates (70% have OM & septic joint) & children
          • From adjacent focus of OM
          • Intra-articular metaphysis
            • Proximal femur, humerus, elbow
    • Transphyseal vessels in neonates
    • Overlying Soft tissue Infection
      • Inoculation
      • Penetrating injury
      • Iatrogenic

Predisposition

  • Three factors
    • Host
      • Immunodeficiency from diabetes, alcohol, malnutrition, etc
    • Site
      • Previous joint trauma, RA, previous HCLA, etc
    • Bacteria

Aetiology

  • Bugs vary with age
    • Staphylococcus aureus most common
    • Unknown in 1/3
  • Community vs Hospital-acquired
  • Neonates
    • Hospital-acquired 60%
      • E coli & Candida
      • S aureus
      • Group B Streptococcus
      • Typically premature or unwell
    • Community-acquired
      • S aureus
      • Group B Streptococcus
      • Usually well
      • 2/3 Osteomelitis
  • Infants & Children < 3 years
    • Staphylococcus aureus > Haemophilus Influenzae
    • Streptococcus pyogenes
    • Streptococcus pneumoniae
    • E coli
    • Proteus
    • Pseudomonas
  • Children >3 years
    • Like adults
  • Adults
    • Staphylococcus aureus > Streptococcus (pyogenes & pneumoniae) > Gram negative (E coli, Proteus, Klebsiella, Pseudomonas)
    • IVDU – Gram negative
    • Sexually active – Neisseria gonorrhoeae
    • Prosthetic joint – Staph epidermidis

Patho>Pathology

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  • Synovium oedematous & hyperaemic
  • Increased cloudy synovial fluid
  • 2/7
    • Frank pus
    • Cartilage destruction
      • Starts at areas of joint contact
  • Synovial membrane replaced by granulation tissue
  • Adhesions wall off pockets of pus
  • Physis destroyed if intra-capsular
  • Fibrous ankylosis
  • Joint dislocation
  • AVN femoral head
  • Cartilage Destruction
    • First glycosaminoglycans of cartilage matrix, later collagen itself
      • Enzymes
        • From WC / Bugs / Cartilage itself
          • Lysosomal enzymes (PG)
          • Collagenases (collagen)
          • Metalloproteases (proteins)
    • Staphylokinase activates plasmin
    • Pressure
      • Unloading/ overloading with immobilisation » degrades cartilage
      • AVN
      • Dislocation
    • Mechanical
      • Immobilization » lack of cartilage nutrition
    • End result = Cartilage Fragmentation

    • Clinica>Clinical Features

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  • Infant
    • History prior infection
      • Eg. Umbilical sepsis
    • Irritability
    • Failure to thrive
    • Low fever ~ Beware
    • Most often affect Hip
    • Joint warm, swollen, & tender
    • Decreased active ROM
    • Decreased passive ROM
    • Muscle spasms
    • Intra-articular pressure
      • Hip abducted 45°/ Flexion 15°/ External Rotation 15°
      • Knee flexion 20°
  • Child
    • As above, but more localized
    • Most often affect Knee
    • 10% involve more than one joint
  • Adult
    • 50% have pre-existing arthritis
    • 30% have Hx of trauma
    • RA may have multiple joint involvement

    • Investigati>Investigations

    s="wp-block-heading">ESR >ESRs="wp-block-list">
  • Usually > 100
  • Not reliable in
    • First 48/24
    • Neonate
    • Steroids
  • Takes weeks to drop
    • Lags behind resolution

    • WCC

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  • Often normal
  • Neutrophils +++
  • PMN leukocytosis

    • Blood Cultu>Blood Culture

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  • Positive 60%

    • Aspiration<>Aspiration

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  • Essential investigation Knee/ Elbow / GHJ
  • ASAP
  • Except Neonate Hip
    • Drain ASAP
    • As aspiration difficult & need GA
  • MCS & Cell count

    • Synovial Fl>Synovial Fluid

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  • Yellow / Grey / Opaque
  • WCC > 50 000 x 10e6/L (usually > 100 000/mm3)
  • Neutrophil usually > 75%
  • Glucose < BSL
  • Protein up usually 6-8g/dL
  • ± Crystals as acid pH decreases solubility
  • Bugs in 30%
  • Culture positive 60%

    • XR

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  • Soft tissue swelling
  • Narrow joint space if > 1/52
  • Later subchondral osteoporosis
  • End-stage bone destruction seen

    • Te99 ScanTe99 Scan

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  • Can differentiate from OM
  • Excellent screen

    • USS

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  • Zarwin Radiology 1993
    • 96 patients with painful hips
    • None of 40 infected hips had normal USS

    • Neonate Hip<>Neonate Hip

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  • Wide joint space ± Subluxed on XR
  • Primary OM in metaphysis
  • Metaphyseal rarefaction
  • Periosteal new bone formation
  • ± Erosion of proximal epiphysis
  • Fluid in joint on USS
  • Te Scan differentiate focal metaphyseal OM
    • Also cold if head dead

    • Differential D>Differential Diagnoses

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  • Acute OM
    • Usually less ↓ ROM
    • Can get symptomatic effusion
    • 70% both
  • Transient Synovitis
    • More ROM
    • Afebrile
    • ESR normal
  • JRA
    • Gradual onset
    • Less systemic features
    • More ROM
  • Perthes
  • Trauma
  • Haemophilia
  • Cellulitis

    • Adults

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  • Gout
    • Especially in knee
    • Peri-articular punched-out lesions
  • Pseudogout
    • Meniscal & articular calcium
  • RA

    • Management

    >Management-block-heading">Antibiotics>Antibiotics-block-list">
  • Start after M/C/S
  • Start broad-spectrum bacteriocidal
    • Gram stain as guide
    • Flucloxacillin & Gentamicin in Adults
    • Flucloxacillin & Ceftriaxone 40mg/kg/dose q24h IV in Children
  • IVAB until systemic toxicity & local swelling subside & CRP normal
    • ~ 2/52
  • Then 6/52 oral AB

    • Drainage

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  • Surgical emergency
  • Arthrotomy or Arthroscopy
    • Small capsulectomy
    • Washout pus
    • ± Synovectomy
  • Close skin only
  • Splint joint in position of function
    • Pain relief
  • Mobilize as pain allows
    • Traditional to immobilize joint to relieve pain in acute phase of disease
    • Salter et al 1981 advocates early passive ROM (via CPM) based on rabbit studies which show that this
    • Improves cartilage nutrition
    • Stimulates chondrocytes to synthesize matrix components
    • Prevents adhesions
    • Helps clear lysosomal enzymes & purulent exudate

    • Prognosis

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  • Worse if
    • Treatment delayed (most important)
    • Hip
    • Associated OM
    • Staphylococcus aureus or multiple organism
    • Neonate as diagnosis delayed & usually hip

    • Outcomes of Septi>Outcomes of Septic Arthritis (of hip)

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  • Normal
  • Growth disturbance
    • Coxa magna
    • Coxa breva
    • LLD
  • Subluxation
  • Dislocation
  • Destroyed epiphysis
    • Secondary Osteoarthritis
  • Ankylosis
  • “Tom Smith arthritis”
    • Arthritis of the hip following neonatal septic arthritis
    • From umbilical manipulation ?
    • Due to delayed diagnosis