Concurrent validity and precision of the thumb disability examination (TDX) in first carpometacarpal osteoarthritis

Study Design: A descriptive psychometric study of precision and concurrent validity of the Thumb Disability Examination (TDX). Introduction: Thumb carpometacarpal osteoarthritis (CMC OA) is a painful joint condition impacting the functionality of the hand. Therapists use patient-reported outcome measures to evaluate change in disability and symptomology in response to interventions. The TDX is the only condition-specific outcome measure for persons with thumb CMC OA. Its responsiveness, test-retest reliability and concurrent validity with the DASH are published, yet it's precision and concurrent validity with a hand-region-specific tool has not yet been established. Purpose of the Study: We aimed to determine the precision and concurrent validity of the TDX with a region-specific outcome measure in people with thumb CMC OA. Methods: Sixteen individuals with a medical diagnosis of CMC OA or a positive pressure-shear test completed the TDX across two visits and the Brief Michigan Hand Questionnaire (bMHQ) at the initial visit. The second visit was 7 to 21 days after the first. Self-administration of the TDX and bMHQ were observed by a licensed occupational therapist. Results: Across total and subscale scores of the TDX, standard error of measurement (SEM) values are used to indicate the precision of tool and demonstrate how confident a user can be that change in score exceeds the error inherent to the tool. Minimal detectable change percentage (MDC%) values for the TDX are acceptable (<30%). The TDX demonstrated high concurrent validity with the bMHQ (r _s = -0.733; P = .001). Discussion: Precision of the TDX is acceptable and the concurrent validity of the TDX with a commonly used region-specific scale is high. The study was limited by a small, demographically homogeneous sample due to difficulty in recruitment. Conclusions: The TDX is a precise and valid outcome measure for individuals having a clinical diagnosis or indications of having thumb CMC OA.