The reliability and validity of a first ray measurement device

The need for measuring the mobility of the first ray has been identified. T he purpose of this study was to test the reliability and validity of a devi ce built to measure the relative vertical displacement of the first ray. Tw enty fresh frozen cadaver feet were sampled (mean age of donor was 70 +/- 1 3 years). Dorsal mobility of the first ray was measured by device over thre e trials of repeated loading using 20 N, 35 N, 55 N and 85 N of force. Radi ographs served as the criterion standard for validation of the device. Vert ical displacement was measured from x-ray by a digitizing procedure that re corded movement of the first ray during loading. Reliability of the device assessed by intraclass correlation coefficients (ICC) was .98 with standard errors of the measurement calculated to be 0.35 mm. A correlation of agree ment value of .97 was determined for the two methods of measurement. Analys is of variance testing found a significant interaction between force and me thod of measurement. Tukey post-hoc analysis found no difference (F < 1.70) between the two methods of measuring first ray displacement in cadaver spe cimens when the force applied did not exceed 55 N. At 85 N of force (F = 10 .05), unwanted movement of the second metatarsal caused the device to overe stimate the amount of displacement that occurred specific to the first ray. This measure of first ray mobility should help clinicians and researchers to better investigate foot pathology resulting from faulty mechanics of the first ray.