The reliability and validity of a first ray measurement device

Area of Science:

• Biomechanics
• Orthopedics
• Podiatry

Background:

• First ray mobility is critical for normal foot function.
• Accurate measurement of first ray displacement is needed for clinical and research applications.
• Existing methods for assessing first ray mobility lack precision.

Purpose of the Study:

• To evaluate the reliability and validity of a novel device designed to measure the relative vertical displacement of the first ray.
• To establish the accuracy of the device against radiographic measurements.
• To determine the device's performance under varying loading conditions.

Main Methods:

• Twenty fresh frozen cadaver feet were utilized.
• Dorsal mobility of the first ray was measured using the device under repeated loading (20 N, 35 N, 55 N, 85 N).
• Radiographs served as the criterion standard, with vertical displacement digitized from X-rays for comparison.

Main Results:

• The device demonstrated high reliability (Intraclass Correlation Coefficient = 0.98) with a measurement error of 0.35 mm.
• Excellent agreement was found between the device and radiographic measurements (correlation of agreement = 0.97).
• The device accurately measured first ray displacement up to 55 N; at 85 N, second metatarsal movement led to overestimation.

Conclusions:

• The developed device is a reliable and valid tool for measuring first ray mobility.
• The device is suitable for clinical and research use, particularly at forces up to 55 N.
• This measurement capability will enhance the investigation of foot pathologies related to first ray biomechanical dysfunction.