The optimal assessment of the rheumatoid arthritis hindfoot: a comparative study of clinical examination, ultrasound and high field MRI

Objectives: The aim of this pilot study was to compare clinical examination (CE) and ultrasound (US) with high field MRI (as the reference standard) for the detection of rearfoot and midtarsal joint synovitis and secondly tenosynovitis of the ankle tendons in patients with established rheumatoid arthritis (RA). Methods: Patients with RA (as determined by the modified American College of Rheumatology (ACR) criteria) with symptoms of midfoot and rearfoot disease were recruited. Demographic data were collected. All underwent CE, US and high field MRI (with intravenous gadolinium contrast) of their right foot. Percentage exact agreement (PEA), sensitivity and specificity were calculated for CE and US when compared to MRI. Inter-reader reliability for CE and US was also assessed. Results: Compared to the gold standard of MRI, for CE (joint synovitis) the ranges for sensitivity, specificity and PEA were 55–83%, 23–46% and 46–60%, and for US were 64–89%, 60–80% and 64–78%, respectively. Compared to the gold standard of MRI, for CE (tenosynovitis) the ranges for sensitivity, specificity and PEA were 0–100%, 20–91% and 55–91%, and for US were 0–67%, 86–100% and 59–86%, respectively. Conclusion: CE was sensitive but US more specific in identifying hindfoot pathology in RA when compared to the reference standard of MRI. There was poor interobserver variability between ultrasonographers suggesting a need for standardisation of acquisition and interpretation of US images of the hindfoot.