Quantitative Measurement of Hoover's Sign: Development of a Standardized Sensor, Interface Procedure, and Testing in Healthy Individuals

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BACKGROUND: Hoover's sign is a commonly used clinical sign for diagnosing functional leg weakness, a feature of functional neurological disorder (FND). However, it relies on clinicians' qualitative assessment. Therefore, more reliable and objective assessment methods are needed. This study aims to develop a portable device and procedure for standardized quantitative measurement of Hoover's sign and validate its utility in healthy controls feigning leg weakness. METHODS: Healthy volunteers without medical backgrounds were recruited. A portable floor-based device with a pressure sensor placed under the heel of one foot was developed to measure hip extension strength during voluntary and involuntary movements. Subjects performed the test under three conditions: healthy, feigning mild weakness, and feigning severe weakness. The involuntary/voluntary ratio (IV/V ratio) and the side ratio (the IV/V ratio of the feigning leg compared to the non-feigning leg) were evaluated. RESULTS: Forty-two subjects were recruited. In the healthy state, the mean IV/V ratio was 0.60 ± 0.23 on the right side and 0.62 ± 0.24 on the left. The IV/V ratio was significantly higher in the feigned leg during both mild (1.26 ± 0.49) and severe (1.83 ± 0.70) feigning compared to the healthy state (p < 0.001 for both), while it was significantly lower in the non-feigned leg during mild (0.40 ± 0.22) and severe (0.32 ± 0.22) feigning (p < 0.001 for both). The side ratio also significantly increased during feigning. ROC analysis revealed optimal IV/V ratio cutoffs of 0.93 for distinguishing mild feigning (sensitivity: 77%, specificity: 93%), and 0.95 for severe feigning (sensitivity: 91%, specificity: 94%). CONCLUSIONS: This portable device can provide a standardized quantitative measure of Hoover's sign and may be useful in future studies of functional leg weakness, particularly in patients with comorbid conditions.