Although MRI and ultrasound offer additional information about disease activity and joint damage, plain radiography is still probably the most used imaging method, and are used in the previous, 1987, grading system for RA (Arnett 1988). Standing radiographs of the foot and ankle can be supplemented by an oblique foot view (not a substitute for a standing lateral) and a standing hindfoot alignment view (Saltzman 1994) to assess the alignment of the ankle and subtalar joint.
Bone destructive lesions in a plain radiograph
E - erosion G - geode
Note that the 2nd and 3rd MTP joints are dislocated
Typical abnormalities on plain radiographs include:
- periarticular erosions
- geodes (areas of osteopenia in the subarticular bone)
- joint space narrowing
There are a number of common scoring systems for plain radiographs. Two of the most popular are the Sharp score, focusing on joint space narrowing in the hand and wrist (subsequently modified by van der Heijde (1999) to include the foot), and the Larsen (1995) score, which includes the hand, wrist and foot and focuses on erosions. Boini (2001) reviewed the evidence on plain radiographic scoring. The Sharp and Sharp/van der Heijde methods were more reproducible than the Larsen method, but took longer to score. Most scores showed similar sensitivity to change in disease.
However, the sensitivity of plain radiography is much lower than MRI, especially in early disease (Nissila 1983). The specificity of all investigations is about 90%, but while the sensitivity of plain radiography is 77% in established disease (Arnett 1988) it falls to 10-20% in early disease (Nissila 1983), compared with over 60% for MRI (Cohen 2011). Combining MRI with serology increases sensitivity to over 80% (Tan 2011). However, not all studies have reported such high sensitivity (Suter 2010). Tan’s review also noted that MRI has been a useful monitor of disease activity in some drug trials.
MRI can demonstrate
- bone oedema
Ultrasound can also detect
- synovial hypertrophy and (especially with the use of colour Doppler) synovitis
(Tan 2011). Grey scale ultrasound is more sensitive than plain radiography in detecting erosions (Wakefield 2000) but less sensitive than MRI (Wakefield 2007). Ultrasound can also be useful in evaluating early arthritis, monitoring treatment and detecting risk of early relapse (summarized in Tan 2011).
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