Assessing Plantar Sensation in the Foot Using the Foot Roughness Discrimination Test (FoRDT): A Reliability and Validity Study in Stroke.

BACKGROUND: The plantar foot represents a sensory dynamometric map and is essential for balance and gait control. Sensory impairments are common, yet often difficult to quantify in neurological conditions, particularly stroke. A functionally oriented and quantifiable assessment, the Foot Roughness Discrimination Test (FoRDT), was developed to address these shortcomings.

OBJECTIVE: To evaluate inter- and intrarater reliability, convergent and discriminant validity of the FoRDT.

DESIGN: Test-retest design.

SETTING: Hospital outpatient.

PARTICIPANTS: Thirty-two people with stroke (mean age 70 years) at least 3 months after stroke, and 32 healthy, age-matched controls (mean age 70).

MAIN OUTCOME MEASURES: Roughness discrimination thresholds were quantified utilizing acrylic foot plates, laser cut to produce graded spatial gratings. Stroke participants were tested on three occasions, and by two different raters. Inter- and intrarater reliability and agreement were evaluated with Intraclass Correlation Coefficients and Bland-Altman plots. Convergent validity was evaluated through Spearman rank correlation coefficients (rho) between the FoRDT and the Erasmus modified Nottingham Sensory Assessment (EmNSA).

RESULTS: Intra- and interrater reliability and agreement were excellent (ICC =0.86 [95% CI 0.72-0.92] and 0.90 [95% CI 0.76-0.96]). Discriminant validity was demonstrated through significant differences in FoRDT between stroke and control participants (P < .001). Stroke fallers had statistically significant higher FoRDT scores compared with nonfallers (P = .01). Convergent validity was demonstrated through significant and strong correlations (rho) with the Erasmus MC Nottingham Sensory Assessment (r = .69, P < .01). Receiver operator characteristic curve analysis indicated the novel test to have excellent sensitivity and specificity in predicting the presence of self-reported sensory impairments. Functional Reach test significantly correlated with FoRDT (r = .62, P < .01) whereas measures of postural sway and gait speed did not (r = .16-.26, P > .05).

CONCLUSIONS: This simple and functionally oriented test of plantar sensation is reliable, valid, and clinically feasible for use in an ambulatory, chronic stroke and older population. It offers clinicians and researchers a sensitive and robust sensory measure and may further support the evaluation of rehabilitation targeting foot sensation.

LEVEL OF EVIDENCE: III.