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
Zone I extends from the tip of the finger to the middle of the 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 the zone I would produce cut to flexor digitorum profundus only.
Zone II
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
Zone III
It extends from the distal palmar crease to the distal edge of the flexor carpal ligament. It is also called the lumbrical zone because of the presence of lumbricals in this zone.
Zone IV
It is the zone under the carpal ligament and carpal tunnel and its contents [9 digital flexors and the median nerve].
Zone V
This zone is proximal to the wrist joint Zone V extends from the origin of the flexor tendons at their respective muscle bellies to the proximal edge of the carpal tunnel.
In the case of thumb, the third zone is very small. See below.
The flexor tendon zones are important from the treatment point of view of flexor tendon injuries.
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My ring finger in zone 3 has been swollen for about 3 months. I can bend it, and I don’t think I broke anything cause I’d be in pain. I was pulling a wagon at fast speeds off and on with a friends grandchild. Could I have pulled something?
With just swelling, no pain or dysfunction, you could afford to wait and watch. If swelling increases in size, get a consultation.