Ultrasonography could be used to predict extended insertion of the EPB tendon noninvasively

An abnormal distal insertion of the extensor pollicis brevis (EPB) tendon into the thumb interphalangeal joint (IP) has been observed in refractory cases of de Quervain's disease. This is associated with the extensor being wider at the midpoint of the proximal phalanx; however, there is no method to noninvasively measure this. This study evaluated the accuracy of measuring the extensor width using ultrasonography, to establish a noninvasive method for predicting an EPB extending the IP insertion.

Of 23 arms from 12 fresh frozen cadavers, the extensor tendon width at the midpoint of the proximal phalanx was measured using ultrasonography and directly at dissection. The association between these values was evaluated using correlation analysis. A cut-off value of extensor tendon width was obtained using receiver operating characteristic analysis.

A strong correlation was observed between the ultrasonography and the measured values. The EPB tendons were normal in 13 arms (57%) and extended in 10 (43%), with a significant difference between these groups in the mean width of the extensor tendon (6.8 ± 1.1 vs. 8.4 ± 1.0 mm). A cut-off extensor tendon width of 8.0 mm yielded an EPB extending the IP.

An EPB extending the IP tendon can be predicted by measuring the extensor tendon width at the midpoint of the proximal phalanx using ultrasonography. The cut-off tendon width value of ≥ 8.0 mm may be useful for assessments prior to surgery and for conservative care.