Diagnosis

Septic Arthritis of Ankle

Case Discription

Septic arthritis is a destructive arthropathy caused by an intra-articular infection that is most commonly bacterial in etiology. Patients typically present with a red, hot, swollen joint that exhibits limited range of motion. Risk factors for a septic joint include bacteremia, immunocompromised status, prosthetic joints, and iatrogenic causes.

Although arthrocentesis with joint fluid analysis is considered the gold standard for diagnosing septic arthritis, MRI is both sensitive and specific and particularly useful in young patients as a means of excluding other diagnoses that don’t require invasive arthrocentesis. It has been reported in the literature that abnormal MRI findings may be present as early as 24 hours after the onset of infection.

MRI findings of septic arthritis include capsulosynival thickening and enhancement, joint effusion (may be complex), low signal subchondral bone on T1-weighted images, and perisynovial edema on T2-weighted images.

Erosions and Bone Destruction with progression to osteomyelitis is one important delayed sequela of Septic Arthritis. The most common organisms is neonates are streptococcus and gram negatives. In Infants and Children, it is Staphylococcus and Aureus, Haemophilus Influenzae, and Salmonella. In Adolescents, it is Staphylococcus Aureus and Neisseria Gonorrhoeae. In Adults, it is Staphylococcus Aureus, Streptococcus and Gram Negative Organisms. In IV Drug Abusers, always suspect pseudomonas and other atypical organisms.

Key Images

4-year-old patient with no known injury complaining of right ankle pain and inability to bear weight.

A. Sagittal T1 image of the right ankle shows marked hypointensity of the distal tibial epiphysis, with  loss of normal epiphyseal T1 hyperintensity (red arrow).  There is also stippled T1 signal within the talus, consistent with osteodema (yellow arrow).
B. Sagittal STIR image shows marked hyperintensity of the chondral epiphysis (red arrow) and an associated complex ankle joint effusion with capsulosynovial thickening and particulate micro-debris (yellow arrow).

References

  1. Karchevsky M, Schweitzer M, Morrison W, Parellada JA. MRI findings of septic arthritis and associated osteomyelitis in adults. American Journal of Roentgenology 2004; 182:119-122