PURPOSE: Finkelstein's test is the classic diagnostic test for de Quervain's 
disease. Finkelstein hypothesized that the entry of the muscle bellies of the 
extensor pollicis brevis (EPB) and abductor pollicis longus (APL) tendons into 
the first extensor compartment was responsible for the findings observed in his 
now eponymous test. We agree with Finkelstein's hypothesis and further 
hypothesize that this position would induce measurable bulk (muscle mass within 
the retinaculum) and tethering (stretching of synovial tissue) effects within 
the compartment. To test this latter hypothesis we measured the excursion and 
gliding resistance of the EPB and APL tendons within the first compartment.
METHODS: Fifteen fresh-frozen cadavers were used. Gliding resistance and 
excursion were measured in 4 different wrist positions, including the wrist 
position of Finkelstein's test (30 degrees ulnar deviation). The bulk and 
tethering effect was calculated based on the mean gliding resistance over the 
tendon proximal/distal excursion cycle and the gliding resistance at the 
terminal distal excursion.
RESULTS: The EPB tendon excursion was significantly more distal in 30 degrees 
ulnar deviation than in 60 degrees extension. Additionally the bulk and 
tethering resistance was significantly greater in 30 degrees ulnar deviation 
compared with 60 degrees extension. For the APL tendon there was no significant 
difference in either the tendon excursion or the bulk and tethering resistance 
between 30 degrees ulnar deviation and 60 degrees extension.
CONCLUSIONS: We showed that in the position of Finkelstein's test the EPB tendon 
is significantly more distal and has significantly greater bulk and tethering 
effect compared with the other EPB positions. This is not the case for the APL 
tendon in the position of Finkelstein's test. These results suggest that an 
abnormal Finkelstein's test reflects differences of the EPB more than it does 
the APL.