Accuracy of diagnosis and evaluation of first ray hypermobility in symptomatic and asymptomatic hallux valgus patients using ultrasonography

Abstract Background Hypermobility of the first ray is related to many foot problems. Existing methods to assess this condition have diverse advantages and disadvantages. The aims of this study were 1) to define the optimal cutoff points for ultrasound evaluation of first ray hypermobility reliant on Klaue device and 2) to evaluate the relationship between the demographic or radiological factors, and hypermobility or forefoot symptoms in patients with hallux valgus. Methods Thirty-two hallux valgus patients were enrolled. Patient's demographic and radiographic data were taken. Hypermobility of the first ray was assessed in all patients using both the Klaue device and ultrasound. Ultrasonographic evaluation, including dorsal translation, plantar and medial gapping of the first metatarsal cuneiform joint, was accomplished. Youden's J statistic was calculated for each sensitivity/ specificity pair to determine the optimal cutoff value for the ultrasound measurements to distinguish hypermobile from non-hypermobile group. Continuous outcome data were analyzed using the two-sample t-test. Categorical outcome data were analyzed using Fisher's exact tests. A separate multivariable logistic regression was used to re-evaluate individual variables that were significant on the univariate analysis while controlling for age, sex, and body mass index. Results The cutoff points for each ultrasound parameter to diagnose hypermobility of the first ray were determined to be ≥ 1 mm increase in dorsal translation (sensitivity = 96.97%, specificity = 82.61%) or ≥ 0.8 mm increase in medial gapping (sensitivity = 72.73%, specificity = 86.96%) or > 1.1 mm increase in plantar gapping of the first metatarsocuneiform joint (sensitivity = 81.82%, specificity = 91.30%). The increase in width of the foot and the increase in hallux valgus angle were correlated with hypermobility of the first ray, while the increase in hallux valgus angle and the first–second intermetatarsal angle were correlated with symptoms in hallux valgus patients. Conclusions The ultrasound technique measuring three parameters of the first ray motion provides acceptable accuracy for the first ray mobility assessment. Width of the feet and hallux valgus angle were associated with hypermobility of the first ray while an increase in the hallux valgus angle and the first–second intermetatarsal angle were associated with symptoms among hallux valgus patients.