6 103 Ultrasonographic Achilles Tendon Thickness: Insertional vs. Midportion Reliability INTRODUCTION Achilles tendon pain related to mechanical loading is commonly referred to as Achilles tendinopathy (AT).1 Patients with AT are classified by location (midportion versus insertional AT) as this might affect the choice of treatment.2,3 Individuals with AT experience a lower quality of life when compared to healthy people and AT has significant socio-economic consequences4,5. There is a need to optimize the diagnostic process for this patient group.6 According to the current guidelines, ultrasound (US) is the preferred imaging method in the diagnostic process of AT.2,7,8 One of the typical findings of AT on US examination is increased tendon thickening, with a cut-off value of approximately 7 mm being accepted as reference standard based on several small cross-sectional studies.7,9-11 Reliability of Achilles tendon thickness measurements using conventional US ranges from fair to excellent.12-14 In the majority of the cases, only the reliability of measuring the Achilles tendon midportion area has been assessed.14,15 No studies have evaluated the reliability of measuring the insertional area in AT patients.14,15 Most of the reliability studies on ultrasonographic Achilles tendon geometry have a high risk of bias (e.g. a very specific selection of participants, inadequate blinding to prior findings/clinical information/ reference standards/additional cues and no time interval between measurements), which limits drawing firm conclusions.14,15 Implementing standardized US procedures is becoming more essential in clinical practice and is a suggested method to improve the reliability of tendon geometry measurements.14,16,17 Ultrasound Tissue Characterization (UTC) is a customized tracking and ultrasonographic data-collection device that facilitates these standardized measurements (see supplementary file 1 for a detailed explanation of UTC).9 To date, it is unknown whether a standardized US method is reliable for measuring Achilles tendon thickness and whether there is a difference in reliability when measuring the midportion versus the insertional area of the Achilles tendon. It is also unknown whether a standardized procedure improves this reliability when compared to conventional US measurements of geometry. The primary aim of this study was to evaluate the intra- and inter-rater reliability of Achilles tendon thickness measurements using UTC in both asymptomatic individuals and patients with AT. The secondary aims were to evaluate if the reliability of thickness measurements differs between the midportion and insertional area and to determine whether tendon thickness measurements using UTC can be translated to conventional US.
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