Intra –og intertester reliabilitet for ultralydsmålinger af patellarsenens tykkelse hos individer med symptomatiske og asymptomatiske patellarsener

Background: RTUS is increasingly used as an available measuring instrument among physiotherapists for diagnosing superficial structures like tendons. Although RTUS is frequently used in scientific studies of patellar tendinopathy, few studies have reported on the reliability of RTUS measurements. Purpose: To examine intra and inter-rater reliability for measurements of the patellar tendon thickness with ultrasonography, on individuals with symptomatic tendons and individuals with asymptomatic tendons. Design: Cross-sectional design - a descriptive study of intra and inter-tester reliability. Method: Sonographic images of 30 symptomatic and 33 non-symptomatic patellar tendons were included. Three raters with varying degrees of experience measured the tendons on longitudinal and transversal images. All three examiners participated in the inter-rater reliability analysis. Two examiners where included in the intra-rater reliability analysis. Results: Intrarater reliability showed a higher reliability for measurements of symptomatic and asymptomatic tendons longitudinally (ICC: 0.88-0.96, SDC: 0.53-1.08mm), than transversally (ICC: 0.87-0.96, SDC: 0.55-2.00mm). The inter-rater reliability displayed a higher reliability for measurements on longitudinal images (ICC: 0.87-0.95, SDC: 0.69-1.03mm) than for transversal images (ICC: 0.84-0.87, SDC: 1.08-2.22mm). Conclusion: Intra and inter-rater reliability was very high, and better for measurements of posterior-anterior tendon thickness longitudinally than transversally on symptomatic and asymptomatic tendons. Reliability was also high for measurements on cross-sectional images, but the measurements was related with a systematic shift between raters and generally subject to a greater margin of error. Measurements of the patellar tendon thickness should be made on longitudinal images where reliable measures are easier to obtain. Repeated measures of the tendon thickness in cross-sectional images should be performed by the same rater. However, because of the low number of raters in this study, the result can only be generalized to the raters included in this study