To determine the prevalence of the ultrasound findings indicating monosodium urate crystal deposits at the popliteal groove region in patients with gout; to evaluate the diagnostic accuracy of ultrasound in detecting monosodium urate crystal deposits at the popliteal groove region, patellar tendon and the knee hyaline cartilage; to investigate the correlation between the ultrasound findings at the popliteal groove region and the clinical features.

Bilateral ultrasound assessment of the popliteal groove region, patellar tendon and femoral condyles’ hyaline cartilage was performed on 47 consecutive patients with gout and 37 controls. The ultrasound findings indicating monosodium urate crystals (aggregates, tophi and “double-contour” sign) were identified according to the Outcome Measures in Rheumatology definitions.

One or more ultrasound abnormalities (aggregates and/or tophi) were found in at least one popliteal groove region in 23 out of 47 patients with gout (48.9%) and in 4 out of 37 controls (10.8%) (P < 0.001). Sensitivity, specificity and diagnostic odds ratio of the ultrasound findings at the popliteal groove region, patellar tendon and at the femoral condyles’ hyaline cartilage were 0.49/0.89/7.9, 0.62/0.81/6.9 and 0.30/1.0/32.0, respectively. There was a significant correlation between the ultrasound findings at the popliteal groove region and history of knee inflammatory involvement (P < 0.001, V = 0.644) and number of gouty “attacks” in the previous year (P = 0.012, V = 0.434).

This study provides new insights into the ultrasound assessment of patients with gout, highlighting the clinical relevance of the popliteal groove region as an area of collection of otherwise undetectable monosodium urate crystals.