Power Doppler ultrasonography of painful Achilles tendons and entheses in patients with and without spondyloarthropathy—a comparison with clinical examination and contrast-enhanced MRI

The objective of this study was to describe ultrasonography (US) and magnetic resonance imaging (MRI) findings at painful Achilles tendons and entheses in patients with and without spondyloarthropathy (SpA and non-SpA) and healthy control persons (CTRLs). Particularly, we aimed to investigate if any changes differentiate SpA from non-SpA. Finally, we investigated the reliability of US compared to clinical examination of Achilles tendinopathy, using MRI as gold standard reference. Twelve SpA patients and 15 non-SpA patients with pain and tenderness at at least one Achilles tendon and/or enthesis due to sports-related causes and 10 CTRLs were examined at the Achilles tendons and entheses with US, MRI and clinical assessment. Intratendinous changes, entheseal changes, bursitis and peritendonitis were assessed. An US interobserver substudy was performed in nine persons. US findings showed high agreement between observers (median 89 %, κ = 0.64) and with MRI (median 89 %, κ = 0.74). All inflammatory intratendinous changes were less frequent in SpA than non-SpA patients (p < 0.05). Entheseal changes and bursitis were found equally frequent in both patient groups except for enthesophytes, which were most common in the SpA group (p < 0.01). No findings were exclusively found in SpA. When MRI was considered gold standard, US showed higher sensitivity for intratendinous and entheseal changes than clinical examination (median sensitivity 0.83 versus 0.66). Especially, entheseal changes had higher sensitivity than clinical examination without loss of specificity. In conclusion, US performed by a trained operator can be a useful adjunct to clinical examination for improved assessment of Achilles tendons and entheses.