Retrocalcaneal bursitis in spondyloarthropathy: Assessment by ultrasonography and magnetic resonance imaging

Objective. To establish by magnetic resonance imaging (MRI) and ultrasonography (US) the frequency of retrocalcaneal bursa involvement in Achilles enthesitis of spondyloarthropathy (SPA) and to compare the results of the 2 examinations. Methods. Nineteen Achilles tendons with severe enthesitis and 9 normal tendons of 14 patients meeting the Amor criteria for SpA were examined by MRI and US. Results. Both MR/and US showed a significant increase in the mean Achilles tendon thickness in the pathologic legs compared to the normal legs both at the superior calcaneal surface and 3 cm above. MRI showed retrocalcaneal bursitis in 14 (73.7%) of 19 pathologic legs and superficial bursitis in 2 (10.5%). US showed fluid collection only in 7 of 14 retrocalcaneal bursae positive on MRI, and failed to show fluid in the 2 superficial bursae involved. Using MRI as the gold standard, US showed 50% sensitivity and 100% specificity for retrocalcaneal bursa involvement and lacked sensitivity for superficial bursitis. Conclusion. Achilles tendon involvement in SpA is not only a disease of the enthesis but also of the adjacent bursae.