114 Chapter 6 Conventional US procedure has similar reliability as standardized US procedure Our study is the first in this field to compare a standardized US procedure (UTC) to the conventional US procedure. Only a limited number of studies have evaluated the application of UTC to the insertional region of the Achilles tendon30,31, as the predominant body of literature primarily examines the use of UTC for identifying alterations in the tendon structure at the midportion.9,27,32 In the current study, the reliability for thickness measurements between the two methods was excellent for the midportion region and good for the insertional region. This means that both procedures can be used in the clinical or research setting. It also emphasizes that our reliability results for the UTC-based approach can be extrapolated to the conventional US procedure. As conventional US is more readily available in most cases and is used in the clinical setting most often, it is useful to know that it is as reliable as the UTC procedure in assessing tendon thickness. Although for the insertional region, there might be a clinically relevant difference between both methods since the SRD was 2.27 mm (more than half of the mean maximum thickness in the patients with insertional AT). Strengths and limitations Our study has several strengths as we adhered to the relevant guidelines for conducting and reporting in reliability studies. The study was large enough to answer the specific research questions.33 Participants and raters were representative and raters were blinded to each other’s and previous measurements and to patient characteristics and additional cues. Nonetheless, this study is subject to certain limitations that warrant consideration. First, thickness measurements of the Achilles tendon using conventional US were only conducted once and by a single physician as part of standardized routine care. Consequently, our capacity to assess intra- and inter-rater reliability for conventional US measurements was restricted, and we were only able to report on reliability between conventional US and UTC based on the measurements taken by that particular researcher. However, we were particularly interested in the translation of standardized (UTC) measurements to daily clinical practice, and we showed that there is an excellent to good reliability between both procedures. Second, the experience in US between both raters ranged from three to 15 years. To reduce potential examiner influence, we used a standardized protocol for collecting and analyzing UTC data. Third, both raters were not blinded to disease status, and the order of examination was not varied, which could have induced information and recall bias respectively. For this reason, we decided to have at least eight months between the measurements of the conventional US and the UTC for one researcher (RJDV) and 16 weeks between the UTC scan and first UTC measurements (TSV). This makes recall bias less likely.
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