This study examined the intratester and intertester reliability of the electronic digital goniometer EDI-320 for the measurement of active neck flexion and extension in healthy subjects. In the context of evidence-based practice, the EDI-320 instrument has the potential to improve patient assessment, provide a clearer picture of patient progress, and confirm the effectiveness of physiotherapy interventions. However, the psychometric properties of the EDI-320 have not yet been documented for cervical spine range of motion. Forty-four individuals with no known history of cervical disorder within the three months prior to the testing, voluntarily consented to participate in this study. Repeated measurements with the EDI-320 were taken by two trained testers (TH1 and TH2) and data were recorded by two separate observers. Subjects performed a standardized warm-up. Testers were required to repeat palpation of bony landmarks prior to each trial. Measurements were taken at the end-range of active cervical flexion and extension for each subject. Both testers measured each subject twice. The intraclass correlation coefficients (ICC) were derived from one-way ANOVA for intratester reliability and a two-way ANOVA for intertester reliability. Paired t -tests were then applied to verify for systematic error. Moderate intratester reliability was found for both testers for flexion (TH1: ICC=0.77; 95% CI: 0.62-0.87; TH2: ICC=0.77; 95% CI: 0.58-0.87). As for extension, high intratester reliability was found for TH1 (ICC=0.79; 95% CI: 0.65-0.88) and moderate for TH2: (ICC=0.83; 95% CI: 0.63-0.92). Intertester reliability results showed a moderate reliability for both flexion and extension (ICC=0.66; 95% CI: 0.24-0.84) on the first trial. On the second trial, reliability was moderate for flexion (ICC=0.73; 95% CI: 0.53-0.85) and high for extension (ICC=0.80; 95% CI: 0.64-0.89). The t -test analysis revealed the inclusion of systematic error by Tester 2 for intratester reliability. This error was also found for all but one of the intertester reliability calculations. This study has shown that the EDI-320 is a moderately reliable instrument for quantifying cervical flexion and extension range of motion. The presence of systematic error in the study highlights the importance of following standardized procedures and suggests that the EDI-320 could be more reliable than reported in this study. Further psychometric studies investigating the validity of the EDI and reliability with subjects affected by cervical pathology is warranted.
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