Reliability and validity of pinch and thumb strength measurements in de Quervain's disease.

The purpose of this study is to evaluate the test-retest reliability and construct validity of pinch and thumb strength measurements in subjects with de Quervain's disease. Maximal palmar pinch and thumb strength (adduction, extension, abduction, and flexion) were measured using, respectively, a pinch gauge and a biaxial dynamometer. The reliability was estimated using the generalizability theory. The validity hypotheses were as follows: 1) the pinch and thumb strength of the symptomatic side would be significantly lower than that of the asymptomatic side, and 2) the strength loss would be greater for thumb extension and abduction. The reliability was high for all strength measurements, pinch strength being the more reliable one. The pinch and thumb strength in all directions evaluated was significantly decreased on the symptomatic side (p<0.003); no direction showed a greater decrease than the others. The results suggest that pinch and thumb strength measurements are reliable and able to show a decreased strength on the symptomatic side in this population.