Extensor pollicis brevis tendon can hyperextend thumb interphalangeal joint in absence of extensor pollicis longus: Case report and review of the literature

Table 1 Previous anatomic studies of extensor pollicis brevis insertional anatomy

Ref.	Type of study	# of hands	EPB insertion site
Stein[3]	Cadaver study	42 cadavers, 84 wrists dissected	No comment on insertional anatomy
Dawson et al[4]	Cadaver Study	16 hands of eight cadavers	56% inserted partly to the base of the first phalanx and partly to the extensor hood 25% inserted entirely on the base of the thumb proximal phalanx 19% inserted entirely onto the extensor hood 5% were absent - the Abductor pollicis longus tendon instead inserted partly to the extensor hood and partly to proximal phalanx Four out of the eight cadavers showed asymmetry of the EPB between right and left hands
Brunelliet al[5]	Cadaver study	52 hands	19% inserted onto proximal phalanx with most also having attachments to extensor hood 69% inserted into the extensor hood 8% inserted into the base of the distal phalanx 4% were absent
Kulshreshtha et al[6]	Cadaver study	44 hands 23 cadavers	25% inserted onto proximal phalanx 25% of tendons insert partly to the base of the proximal phalanx and partly to the extensor hood 2% of tendons inserted entirely into extensor hood 27% of tendons inserted partly to the base of the proximal phalanx and partly to the extensor hood, and from there, continuing further to the base of the distal phalanx with EPL 20% of tendons inserted into the extensor hood and, from there, continued further to the base of the distal phalanx with EPL The EPB was present in all hands, but anatomy of the EPB is variable on the left and right sides of 14 of the 21 paired hands
Alemohammad et al[7]	Clinical study and Cadaver study	90 cadaver wrists, and 143 patients undergoing Dequervain’s release surgery	In the cadaver group - in 21% pulling on the EPB tendon produced thumb IP joint extension 79% inserted onto proximal phalanx 17% inserted onto distal phalanx 4% inserted onto extensor hood
Shigematsu et al[8]	Cadaver study	72 cadaver specimens, 144 hands	29% inserted entirely onto the extensor hood 22% inserted onto the base of the proximal phalanx 19% inserted partly onto the base of the proximal phalanx and partly into the extensor hood 9.0% inserted onto the base of the proximal phalanx and into the extensor hood, and then on the base of the distal phalanx, along with EPL 9.0% inserted onto the extensor hood, and then onto the base of the distal phalanx, along with the EPL 2% were completely absent with no accessory tendon 6% were absent but an accessory tendon inserted at the MP joint 4% had 2 EPB tendons - with variable insertions

EPB: Extensor pollicis brevis; EPL: Extensor pollicis longus.