The distal phalanx is divided into three anatomical parts: most proximally,
the metaphysis, followed by the diaphysis (“waist”), and finally the ungual
The base of the distal phalanx has a prominent crest on the dorsal aspect
with the insertion of the terminal extensor tendon. The tendon is adherent to
the joint capsule.
On the palmar surface is the insertion of the flexor digitorum profundus
tendon. This is adherent to the volar plate and to the periosteum.
The flexor tendon occupies the whole width of the base of the distal phalanx.
It is made up of 2 different fibers. The superficial fibers attach to the
lateral aspects of the phalanx. The deep fibers run centrally and attach more
distal in the palmar aspect of the phalanx.
The volar plate is very flexible, allowing hyperextension of the DIP joint to
allow pulp-to-pulp pinching, which is unique to humans. This flexibility is
also facilitated by the absence of check reins, which might be attached to the