Ultrasonography and MRI are used for imaging evaluation of patellar tendinopathy, and "thickening of the tendon" is known as one of the characteristic findings. However, there are no evidence-based quantitative criteria to help evaluate this phenomenon. The purpose of this study was to investigate an objective measure of patellar tendon thickness. Patellar tendon thickness was evaluated in 65 elite university athletes using both ultrasonography and MRI. The relationship between tendon thickness and clinical patellar tendinopathy was investigated, and the cutoff value of the tendon thickness was calculated. Of the 129 knees included in the analysis, clinical patellar tendinopathy was found in 16 knees (12.4%). The proximal patellar tendon was significantly thicker in athletes with clinical patellar tendinopathy on both ultrasonography (8.3 mm vs. 5.1 mm; p < 0.001) and MRI (9.9 mm vs. 5.5 mm; p < 0.001). Setting the cutoff value to a thickness of >7.0 mm was an accurate predictor of clinical patellar tendinopathy (ultrasonography: sensitivity 81.3%, specificity 95.6%; MRI: sensitivity 100%, specificity 89.4%). Both ultrasonography and MRI measurement of the proximal patellar tendon thickness reflected the presence of clinical patellar tendinopathy. Defining "thickening of the patellar tendon" as thicker than 7.0 mm on both ultrasonography and MRI therefore has clinical significance.
Keywords: MRI; patellar tendinopathy; patellar tendon thickness; ultrasonography.