There are five flexor tendon zones in hand.Flexor tendon zones influence prognosis following flexor tendon repair. The five flexor tendon zones apply only to the index through small fingers as separate zones exist for the thumb flexor tendon.
Zone I extends from the tip of the finger to the middle of middle phalanx. This zone consists of the profundus tendon only and is bounded proximally by the insertion of the superficialis tendons and distally by the insertion of the flexor digitorum profundus tendon into the distal phalanx.
As it contains only flexor digitorum profundus, injuries in zone I would produce cut to flexor digitorum profundus only.
Zone II extends from the middle of the middle phalanx to distal palmar crease. It contains both flexor tendon superficialis and flexor tendon profundus. Proximal to zone II, the flexor digitorum superficialis tendons lie superficial to the FDP tendons. Within zone II and at the level of the proximal third of the proximal phalanx, the FDS tendons split into 2 slips, collectively known as Camper chiasma. These slips then divide around the FDP tendon and reunite on the dorsal aspect of the FDP, inserting into the distal end of the middle phalanx.
It has been called “No Man’s Land” or “No Man’s Zone” because repair in this zone is very difficult.
Both the tendons are interwoven and surrounded by a number of pulleys in this zone
It is the zone under the carpal ligament and inclupal tunnel and ides carpal tunnel and its contents[ 9 digital flexors and the median nerve].
In case of thumb the third zone is very small. See below.
The flexor tendon zones are important from treatment point of view of flexor tendon injuries.