Intra-rater variability of sonographic measurements of the Achilles tendon

Introduction: To evaluate adaptation to strength training in clinical diagnostics and follow-up of Achilles Tendinopathy repeated sonographic measurements of the tendon diameter are regularly performed [1]. However, limited data on validity criteria, especially intra-rater variability of anteroposterior (a.p.) diameter of the Achilles tendon (AT) are available. It is unclear whether longitudinal and transversal transducer placements represent reliable methods to measure AT a.p. diameter. Therefore, the purpose of the study was 1. to assess validity of transversal scan of AT a.p. diameter compared to longitudinal transducer placement (standard [2]) and 2. to evaluate the intra-rater variability of both measurements. Methods: The AT a.p. diameter of 14 healthy recreationally active subjects (28.1 ± 4 years; 170.4 ± 9 cm; 68.3 ± 12 kg) was measured at baseline and after 3 days of follow-up (8-MHz transducer, Xario, Toshiba) by the same experienced examiner. Diameter was measured in two different conditions (longitudinal versus transversal) 2 cm proximal the insertion [2]. Differences were tested by one-way ANOVA (α = 0.05). To evaluate reliability of measurements test-retest-variability (TRV), ICC and 95% limits of agreement (LOA [3]) were calculated. Results: AT a.p. diameter measured with transversal scans was not different from results of longitudinal transducer placement (p > 0.05; Table 1). Intra-rater-TRV ranged from 3.3–5.8%, ICC from 0.74 to 0.89. LOA were narrow between measurement days, transducer position and sides (Table 1).