Finkelstein's test: a biomechanical analysis.

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.