Sensitivity And Specificity Of Diagnostic Imaging Techniques For Patellar Tendinopathy

Abstract

PURPOSE Patellar tendinopathy (PT) is a common condition that is characterized by activity-related anterior knee pain associated with focal patellar tendon tenderness. While clinical examination forms the cornerstone of diagnosis in PT, imaging is frequently used for differential diagnosis with the techniques of choice being ultrasonography (US) and magnetic resonance imaging (MRI). The usefulness of these techniques are not established with positive US and MRI images for PT being shown in asymptomatic tendons, and symptomatic tendons having the imaging appearance of normal asymptomatic tendons. The primary aim of this study was to establish the sensitivity and specificity of US and MRI for the diagnosis of PT. A secondary aim was to assess the usefulness of color Doppler US in the diagnosis. METHODS Twenty subjects with symptomatic PT were recruited according to appropriate inclusion and exclusion criteria. A control group consisted of 20 activity- matched asymptomatic controls. All subjects had their patellar tendon imaged using US (grey-scale and color Doppler) and MRI (proton-density weighted and STIR), according to standard protocols. One investigator performed all US (ZSK) and two investigators reviewed the MRI scans (ZSK and FM). These investigators were blinded to pathology group at all times. Intra- and inter-tester reliability of MRI was performed on 10 random scans from each symptom group reviewed one week apart, and the sensitivity and specificity of each imaging techniques was determined. RESULTS Intra- and inter-tester reliability of MRI was moderate to good for most qualitative and quantitative assessments. The exceptions were for transverse width and cross-sectional area of the lesion, which had poor inter-tester reliability. US had a sensitivity and specificity of 0.79 and 0.82 for confirming symptoms of PT, respectively. The positive and negative predictive values for US were 0.75 and 0.85, respectively. In contrast, MRI had a sensitivity and specificity of 0.50 and 0.71, respectively, with positive and negative predictive values of 0.77 and 0.70, respectively. Color Doppler US was the most specific for symptomatic PT with 92%of symptomatics having a lesion. CONCLUSIONS The results of this study suggest that US should be the imaging modality of choice in the differential diagnosis of PT. It was more sensitive and specific, and is less costly, quicker and more readily available than MRI. It also allows for concurrent use of color Doppler US which seems highly specific for symptomatic PT.