Reliability of Thickness Measurements of the Abductor Hallucis Muscle Using the Spring Gauge Technique in Hallux Valgus Subjects: An Ultrasonographic Study

Purpose: The purpose of this study was to determine the intra- and inter-rater reliability of muscle thickness (MT) measurements of the abductor hallucis (AbdH) in subjects with hallux valgus (HV), using ultrasonography performed at different inward pressures of approximately 0.5 kg, 1.0 kg, 1.5 kg, and 2.0 kg, with no pressure control. Methods: Thirty-two subjects with HV were recruited. The thicknesses of both sides of the AbdH were measured randomly by two different examiners for assessment of the intra- and inter-rater reliability. The measurement values were analyzed using the intra-class correlation coefficient (ICC) with a 95% confidence interval (CI). ICC (2,1) was used to determine the inter-rater reliability of MT measurements of the AbdH, while ICC (3,1) was used to assess the intra-rater reliability. Results: The results showed higher ICC values for intra-rater reliability compared to inter-rater reliability, and the value for inter-rater reliability with no pressure control (ICC=0.74 [95%CI=0.53-0.87]) was smaller compared to pressures of 0.5 kg, 1.0 kg, 1.5 kg, and 2.0 kg. Other inward pressures for intra- and inter-rater reliability also showed excellent values (ICC=0.86-0.96). Conclusion: The findings showed that maintaining consistent inward pressure is essential for reliable results in measurement of the MT of the AbdH by different examiners in a clinical setting.