• Shiro Sugiura, Yusuke Matsuura, Kazuki Kuniyoshi, Satoru Nishikawa, Takeshi Toyooka, Chisato Mori, and Takane Suzuki.
• Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-Ku, Chiba, 260-8670, Japan.
• Surg Radiol Anat. 2017 Nov 1; 39 (11): 1223-1226.

IntroductionThe extensor pollicis brevis (EPB) tendon normally inserts into the base of the proximal phalanx of the thumb. However, a distal insertion of the EPB tendon into the thumb interphalangeal joint has been reported in refractory cases of de Quervain's disease. We hypothesized that the EPB tendon is wider beyond the thumb metacarpophalangeal joint in patients with extended EPB. This study aimed to evaluate the relationship between the extensor tendon width and the point of distal insertion of the EPB tendon.Materials And MethodsIn 45 hands from 18 male and 27 female adult cadavers, the first extensor compartment was dissected and the existence of the intertendinous septum was assessed. The extensor tendon width was measured at the midpoint of the proximal phalanx, and relationships between extended EPB tendon, existence rate of the intertendinous septum, sex, and extensor tendon width were examined.ResultsOf 45 cases, intertendinous septum and extended EPB tendon were observed in 37 (82.2%) and 23 (51.1%), respectively. There was no significant difference between the existence rates of both these factors and sex. The mean extensor tendon width in the extended EPB group was significantly greater than in the normal EPB group. The cut-off value of extensor tendon width in the extended EPB group was 7.12 mm.ConclusionsThe extensor tendon width was wider in the extended EPB group than in the normal EPB group, suggesting that the differences in the EPB tendon width can be used to identify various anatomical variations in extended EPB.

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