Morphometry of extensors of the thumb with comprehensive review

This study was aimed to evaluate the anatomical variations and morphometry of long extrinsic tendons of the thumb namely, extensor pollicis longus and extensor pollicis brevis. Fiftyfive upper limbs of formalin embalmed adult cadavers were dissected. The variation in muscle belly, tendon, its course within dorsal wrist compartment and mode of insertion were noted. The extensor pollicis longus was duplicated in 5.5%. Around 25% tendons were fused with extensor pollicis brevis and through the extensor hood insert into the base of the distal phalanx. The extensor pollicis brevis was absent in 2% and tendon was also duplicated in 2%. In case of absent extensor pollicis brevis tendon, one of the slips from the abductor pollicis longus insert into base of the proximal phalanx instead of the extensor pollicis brevis. The extensor pollicis brevis tendon showed various modes of insertion. The overall length of the extensor pollicis longus and extensor pollicis brevis were 121 mm and 90 mm respectively. The thickness of the extensor pollicis longus at the proximal, middle and distal level of insertion were 1.25 mm, 0.76 mm and 0.55 mm respectively, whereas for the extensor pollicis brevis it was 1mm, 0.75 mm and 0.53 mm. The results obtained from this study may be helpful for the hand surgeons in the management of extensor tendon injuries of the thumb, its reconstructive procedures and in differential diagnosis of dorsal wrist pain.