Background Posterior heel pain is a common symptom in the foot and ankle region, with many different causes that need to be distinguished by differential diagnosis. Among them is ankylosing spondylitis (AS), in which enthesitis of the heel is common and occasionally is responsible for their initial symptom to seek clinics. An early or timely recognition of active enthesitis of AS from simple radiographs comes to be relevant issue.
Objectives The purpose of current study is to assess measurement reliability and diagnostic validity for detecting the digital radiographic findings of enthesitis at the Achilles tendon insertion in patients with AS.
Methods Current study is a blinded, matched, cross-sectional study with 44 patients (65 feet) having clinical enthesitis at the Achilles tendon insertion (Group I), and 44 healthy controls (65 feet) (Group II). Suggested findings of enthesitis including retrocalcaneal recess obliterations from retrocalcaneal bursitis, increased thickness in shadow of the Achilles tendon and posterior soft tissue at its insertion from the swellings of those soft tissues were assessed on digital radiographs of standing hindfoot lateral view, and their measurement reliabilities were determined. To investigate diagnostic validities, diagnostic odds ratio, sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) were estimated for radiographic findings of retrocalcaneal recess obliterations (RRO). For the thickness of the Achilles at its insertion (TAI) and swollen posterior soft tissue, the receiver operating characteristic (ROC) curve analysis was done.
Results There were no significant differences between two groups in mean age, BMI and sex ratio. Intra- and inter-observer reliability of all measurements showed high degree of agreements (0.786 to 0.941). The diagnostic odds ratio of RRO for detecting enthesitis was 66.0. The sensitivity, specificity were 67.7%, 96.9%, and PLR, NLR were 22.0, 0.33, respectively. The mean TAI of Group I and II were 6.7mm±1.79, 5.01mm±0.81, respectively (p-value<0.001). Area under the ROC curve of the TAI was 0.806, and the optimal cut-off value predicting enthesitis was 5.47mm, and its sensitivity and specificity were both 72.3%.
Conclusions Retrocalcaneal recess obliteration and thickened shadow of Achilles tendon at its insertion and swollen posterior soft tissue on digital radiographs of standing hindfoot lateral view are regarded as the easy and useful findings for enthesitis of the posterior heel. For searching enthesitis at the Achilles insertion in patients with AS, such findings from simple radiographs showed high measurement reliability and validity.
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Disclosure of Interest None declared