A New, Direct Measure of Thumb Use in Children After Index Pollicization for Congenital Thumb Hypoplasia

Purpose: After index pollicization for congenital thumb hypoplasia, time-based hand dexterity tests do not indicate whether the new thumb is being used by a child. The Thumb Grasp and Pinch assessment (T-GAP) is a new outcome measure that classifies grasp and pinch styles to quantify use of the new thumb. The goal of this study was to establish concurrent validity and construct validity in the T-GAP. Methods: Data from children treated with index finger pollicization for congenital thumb hypoplasia were retrospectively reviewed. Measures of strength, range of motion, and scores on the Box and Blocks Test (BBT), 9-Hole Peg Test (NHPT), Functional Dexterity Test (FDT), and Task 7 (Heavy Objects) from the Jebsen-Taylor Test (JTT7) were recorded. Patients also completed the T-GAP consisting of 9 age-appropriate tasks, during which grasp patterns were classified. Spearman correlation coefficients were calculated comparing the T-GAP score with scores on the BBT, NHPT, FDT, and JTT7. Results: We evaluated 21 thumbs in 21 children an average of 71.7 months after pollicization surgery (range, 9–175 months). The T-GAP score was significantly correlated with BBT, NHPT, FDT, and JTT7 (R = 0.69, –0.60,–0.59, and –0.60, respectively). The T-GAP score was significantly correlated with tripod pinch, key pinch, and grip strength (R = 0.77, 0.75, and 0.71, respectively) and with opposition and grasp span (R = 0.50 and 0.52, respectively). The T-GAP was the only functional measure correlated with parent and patient satisfaction with thumb function. Conclusions: Concurrent validity was supported by significant correlations between T-GAP score for all 4 dexterity measures. Construct validity was supported by significant correlations between strength and range of motion of the thumb and T-GAP score. Clinical relevance: This evaluation may help surgeons and therapists better understand results after pollicization and determine whether the new thumb is being incorporated into daily activities.