Background: Excessive first ray mobility has been implicated as the cause of many forefoot abnormalities. The association between hypermobility and forefoot pathology is controversial, and this is largely related to the difficulty in quantifying first ray motion. Manual examinations have been shown to be unreliable. Klaue etal. developed a device consisting of a modified ankle-foot orthosis with an attached micrometer to objectively measure first ray mobility. The purpose of this study was to evaluate the validity and reliability of this device.
Methods: Sixteen fresh-frozen, below-knee amputation specimens with hallux valgus were used for the study. The study was divided into two parts. Part I was an analysis of the validity of the Klaue device; first ray dorsal displacement was measured on lateral radiographs following manual manipulation, and values were statistically compared to the Klaue device measurements. Part II of the study was an evaluation of intraobserver and interobserver agreement. Two clinicians used the Klaue device on each of the cadaver limbs, and values of first ray sagittal mobility were recorded and compared.
Results: The mean value of first ray mobility measured with the Klaue device was 7.5 mm and the average displacement measured from the lateral radiographs was 7.4 mm. Paired t-testing showed no significant difference between the Klaue and radiographic measurements (p = 0.83). The mean first ray mobility by examiners 1 and 2 with the Klaue device were identical (10.5 mm), and statistical analysis showed no significant interobserver or intraobserver differences.
Conclusions: The results confirm the validity of the Klaue device and limited variability of measurements between experienced users.