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

Abstract

Study DesignA descriptive psychometric study of precision and concurrent validity of the Thumb Disability Examination (TDX). IntroductionThumb 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 StudyWe aimed to determine the precision and concurrent validity of the TDX with a region-specific outcome measure in people with thumb CMC OA. MethodsSixteen 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. ResultsAcross 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 (rs = -0.733; P = .001). DiscussionPrecision 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. ConclusionsThe TDX is a precise and valid outcome measure for individuals having a clinical diagnosis or indications of having thumb CMC OA.