Validity and Reliability of the Thumb Grasp and Pinch Assessment for Children After Reconstruction of Congenital Hypoplastic Thumbs

Purpose: The Thumb Grasp and Pinch Assessment (T-GAP) is a new instrument for evaluating thumb use in children with congenital hypoplastic thumbs. The assessors video-record the children while they perform nine specific activities and score their grasp types using T-GAP. A high T-GAP score indicates more mature grasp patterns. The developers reported the instrument's validity and reliability for index finger pollicization. This study investigated T-GAP's validity and reliability in children with reconstructed hypoplastic thumbs.

Methods: Four hand surgeons and two hand therapists from two hospitals rated video clips of 20 Manske type II and IIIa hands twice in 17 patients who performed the T-GAP at least 1 year after opposition transfer and thumb ligament reconstruction. To investigate the validity, we calculated correlation coefficients for T-GAP scores and clinical outcomes, including thumb ROM, grip and pinch strength, and visual analog assessments of thumb function and appearance. To estimate T-GAP's inter- and intrarater reliability, we calculated intraclass correlation coefficients and their 95% confidence intervals (CIs).

Results: Thumb Grasp and Pinch Assessment score showed a strong linear correlation (r = 0.815-0.944) and a moderate to strong nonlinear correlation (ρ = 0.527-0.744) with visual analog scale assessments of thumb function and appearance, respectively; a moderate nonlinear correlation (ρ = 0.464) with grip strength; and a moderate nonlinear correlation (ρ = 0.541) with thumb MCP joint range of motion. The intraclass correlation coefficient for the interrater reliability was 0.892 (95% CI, 0.768-0.954) in round 1 and 0.898 (95% CI, 0.754-0.959) in round 2, and for intrarater reliability, the mean was 0.882 (95% CI, 0.785-0.980).

Conclusions: Thumb Grasp and Pinch Assessment score had a moderate to strong construct validity and a moderate concurrent validity. Both inter- and intrarater reliability was strong.

Clinical relevance: This study supports the T-GAP instrument's validity and reliability for assessing functional outcomes in congenital hypoplastic thumb reconstruction.