The X Files: June 2009

Marshall Deltoff
June 17, 2009
Written by Marshall Deltoff
This 43-year-old construction worker presented with a painful, swollen, reddened foot and decreased ROM, a few days after stepping on a nail at a worksite.

footinfection1  
Figure 1
 

Here are a few points to remember about septic arthritis:
  • also known as pyogenic or infectious arthritis
  • most (90 per cent) are due to Staphylococcus aureus
  • in long bones, the organism lodges in the metaphysic, due to its high vascularity
  • organism spreads hematogenously to the vasculature of the synovial membrane
  • capsular distention ensues as a result of purulent exudate; the exudate interferes with cartilage nutrition, resulting in death of chondrocytes and causing a release of proteolytic enzymes; therefore, you get progressive destruction of cartilage and bone

On X-ray:
  • early on – soft tissue swelling, joint capsule distention, obliteration of anyjuxta-articular fat planes
  • abscess formation, as a result of pus accumulation, produces increased juxta-articular soft tissue density
  • local periarticular osteoporosis (due to regional hyperemia, proteolytic enzyme release and disuse), often in a moth-eaten pattern
  • destruction of the articular cartilages invariably results in joint space narrowing, followed by a blurring of intra-articular cortical margins (Figure 1)
  • if the infection subsides early enough, articular surfaces may be remodelled, but there is usually some degree of residual articular deformity
  • if infection is not halted, articular cartilage is eventually completely destroyed,leading to bony ankylosis.

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