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 MRI 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.