Absolute reliability of ultrasound assessment in measuring tibiofibular separation

Abstract

We developed a method for measuring the tibiofibular separation space using ultrasound (US). However, the absolute reliability is unclear. The purpose of this study was to clarify the reproducibility and error range of the measurement of tibiofibular separation by US. Two physiotherapists measured both the feet of 10 healthy participants [5 males and 5 females with a mean age of 25.9 ± 4.8 years (SD)], with no history of ankle problems. Participants slightly flexed their knee in supine position with the ankle was fixed at 35° plantar flexion (PF) and 20° dorsiflexion (DF). Imaging and measurement were randomly performed twice by each examiner using an US (F37, Hitachi Co, Tokyo, Japan). During US scanning, the probe was vertically aligned with the axis of the lower thigh, and the outer side of the tibia was the most protruding part on the side of the fibula. The fibula was aligned horizontally. The recorded image was analyzed only by examiner A using image analysis software (Image J). The interclass correlation (ICC) (1.1), ICC (2.1), Bland–Altman analysis, and minimal detectable (MDC) 95 were applied to determine statistical significance. ICC statistical analyses were performed with PASW Statistics 18. For examiner A, ICC (1.1) was > 0.9 in all image analyses. Both ICC (1.1) and ICC (2.1) in PF and DF conditions were > 0.9. As a result of Bland–Altman analysis, there was no addition//proportional error. MDC95 was 0.62 mm and 0.64 mm in interclass reliability and interclass examiner, respectively. As a result of performing absolute reliability (Bland–Altman analysis and MDC95) in addition to ICC, showed high inter-examiner reliability, with no addition//proportional error. It was found that the error range was ≤ 0.64 mm. The method used in this study was considered to be a reliable method for evaluating tibiofibular separation.