Infection

Infection occurs in 0.5-2% of total knee replacements.14 Diagnosis is frequently challenging, as there is no single clinical or lab test that is definitive for infection. The diagnosis is usually made using a combination of lab tests, clinical and radiographic findings.

  • Laboratory findings
    • Blood tests: generally have low sensitivity and specificity
      • Elevated peripheral blood leukocytes
      • Elevated erythrocyte sedimentation rate
      • Presence of C-reactive protein
    • Joint aspiration
      • Positive cultures useful in patients when infection suspected
      • Beware: unacceptably high rate of false positive results, therefore results must be considered in the appropriate clinical setting15
  • Clinical findings: often absent, these findings may also be seen in aseptic loosening
    • Joint pain and swelling
    • Redness
    • Effusion
  • Radiographic findings
    • 73% of cases have normal plain films or soft-tissue swelling only16
    • Effusion may or may not be evident, and this finding is non specific
    • When radiographic signs are present, they are similar to findings in loosening with progressive interface widening
    • Interfaces tend to be irregular and poorly marginated
    • There are no definitive radiographic signs to differentiate loosening from infection except for soft-tissue gas
    • Soft-tissue gas (ulcer or sinus tract)
    • Laminated periosteal reaction (rare)
  • Treatment
    • Acute, e.g. after dental surgery
      • Open surgical lavage
    • Sub-acute or chronic
      • Resection of hardware with flail knee. Revision arthroplasty after adequate intravenous antibiotic therapy
      • Resection of hardware and placement of cement spacer. Revision arthroplasty after adequate intravenous antibiotic therapy

Cement spacers are temporary prostheses made of antibiotic-impregnated methymethacralate. The cement is prepared in the surgical suite, mixed with antibiotics, and formed by the surgeon into a patty, cylinder or forms resembling the femoral and tibial components of a total knee replacement. The spacer allows for local dispersal of antibiotic to the infected joint area. Cement spacers have certain advantages because they:

  •  Provide local dispersal of antibiotics to the infected joint area
  • Maintain leg length
  • Minimize dead space
  • Preserve soft-tissue planes
  • Facilitate ease of revision arthroplasty

Infection. Note subtle irregular, progressive interface widening over 2-month period.

      July above left and below left; September above right and below right.

 

Gas (arrows) in neo capsule of total knee replacement secondary to sinus tract from joint to skin.

Gas producing soft-tissue infection in patient with diabetes.

Infect TKR with markedly widened and irregular interfaces of the femoral, tibial and patellar components.

Infected TKR with subtle periosteal reaction.

Cement spacer in place status post removal of infected prosthesis.

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