Hip Arthroplasty after Infection

Types of infection

Osteomyelitis

  • Organisms
    • S.aureus causes 90%
    • S. epidermidis & streptococci
  • If recurrence occurs after infection it is likely to do so within the year
  • THR after osteomyelitis
    • 20% chance of recurrence
      • Of the recurrences
        • 60% did so by 6 months
        • 80% by one year
    • In 50% of cases there was only one episode of recurrence.

Septic arthritis

  • Organisms
    • Most common organism is S.aureus
    • S.aureus in 77% of septic hips, g –ve in 16% & streptococci in 4%
  • Sequelae of septic arthritis in immature hips
    • trochanteric overgrowth
    • acetabular dysplasia including protrusio
  • Infection of the hip joint is particularly bad. Morrey found poor results in half of children with infected hip as opposed to 20% poor results in other joints

Tuberculosis

  • 400 cases of skeletal TB/year in USA. Infection with HIV leads to an ↑ in the reactivation rate of TB
  • main distinguishing fact of TB on plain XR is the marked bony destruction which can mimic a malignant tumour

Factors predisposing to recurrent infection

Intravenous drug abuse

Haemoglobinopathies

  • 20/70 patients with severe haemoglobinopathies followed for 10 years developed osteomyelitis
  • Gram-negative infections predominate, in particular Salmonella (8 of 10 fully documented cases).

Ongoing sources of infection

  • Risk is present but not overwhelming
  • distant infection resulted in a x 3 ­
    • organisms were not necessarily the same

Exclusion of active infection

Clinical

  • Rapid ↑ in pain, systemic symptoms

Investigations

Blood Tests

  • WCC – not particularly useful
  • CRP & ESR – Spangehl JBJSA1999 suggests that a normal ESR & CRP effectively rules out infection.

Plain radiographs

  • are not helpful

CT scans

  • may demonstrate soft tissue abscess or oedema

MRI

  • is very sensitive & may be quite useful
  • Sensitivity of 95% & specificity of 88% for active infection.
  • Active infection appears dark on T1 & bright on T2; with chronicity the bright T2 marrow signal becomes more heterogeneous.

Nuclear medicine

  • Best way of differentiating infection is with a sequential technetium bone scan followed by an Indium labeled white cell scan

Aspiration biopsy

  • Controversial
  • In the setting of revision arthroplasty for sepsis there was a sensitivity of 86% & a specificity of 94% in detecting sepsis.

Mantoux test

  • Performed if suspected TB infection

Links

Periprosthetic Infections