The Membrane-Like Structure From Extensor Tendon to the Nail in the Distal End of Digits: An Anatomical Study for the Structure, Function and Utility.

In distal dorsal finger injuries, the delicate structures of the nail matrix or insertion of the extensor tendon to the distal phalangeal bone should be preserved or repaired for esthetic and functional results. To explore these structures for a safer surgical approach, we focused on a membrane-like structure (the superficial extended portion of the extensor tendon [SEP]), poorly described previously, that attaches between the nail halter and the extensor tendon. METHODS The nail structures of 6 cadavers were investigated in each of the 10 digits of the hand. In the histological study, the thickness, length, and location of the SEP were measured in each digit of 3 cadavers. In the other 3 cadavers, the moving distance of the SEP was measured macroscopically with the distal interphalangeal joint in flexion at 0 to 60 degrees for confirmation of the function. This moving distance could be considered as an indicator of the SEP straining the surrounding (retaining) structure and improving the stability of the nail in pinches. RESULT The SEP was recognized in all the digits. The average length of the SEPs was 2.38 ± 0.11 mm (mean ± SE). The average thickness of the SEPs was 0.35 ± 0.02 mm. The nail matrix and its feeding artery were found beneath the SEP in all digits. The average moving distance of the SEP was 1.38 ± 0.06 mm. This moving distance could be considered sufficiently large to support the role of SEP in the pinches compared with the excursion of the extensor tendon at the DIP joint in a previous report. CONCLUSIONS The SEP has been shown to play an essential role in fingertip stabilization in pinches. It can serve as an anatomical marker to avoid iatrogenic damage to the nail matrix in surgical approaches.