Criterion-related validity of a clinical measure of dorsal first ray mobility

Study Design: Test-retest methodological design using a sample of convenience. Objective: To determine the criterion-related validity and the reliability of measuring first ray mobility with a ruler. Background: Studies have questioned the accuracy of assessing first ray mobility by manual examination. Use of a ruler and adherence to strict guidelines in positioning of the patient may improve the measure. This study investigates the validity, and the intrarater and interrater reliability of measuring dorsal first ray mobility with a ruler while following recent recommendations to standardize the position of measurement. A valid and reliable mechanical device designed to measure first ray mobility was used as the validation criterion of measurement. Methods: Three clinicians performed ruler measurement of dorsal mobility on 14 subjects. A separate examiner measured dorsal mobility with the mechanical device. Intraclass correlation coefficients (ICCs) and standard error of measurements (SEMs) were computed to quantify the intrarater reliability of both testing procedures and the interrater reliability of the ruler measurement. ICCs of agreement were also computed to determine the concurrent validity of the ruler measurement for each clinician. Results: Mechanical device intrarater reliability ICC was 0.98 (SEM = 0.15 mm). Ruler intrarater ICCs were equal or less than -0.06 (SEMs = 1.1 mm); ruler interrater ICC was 0.05 (SEM = 1.2 mm). The ICCs of agreement between the mechanical device and ruler method ranged from -0.44 to 0.06. Conclusion: The ruler method of testing demonstrates poor reliability and validity as a clinical measure.