Zone classification of flexor tendon injury

Last revised by Leonardo Lustosa on 13 Aug 2023

The zone classification of flexor tendon injuries divides injuries into five zones based on anatomical location. It is the most widely used flexor tendon injury classification system (c. 2007) 1.


Flexor tendon injuries were classified into five zones by Kleinart and Verdan in 1983 1,4:

  • zone I
  • zone II: starts from the A1 pulley proximal edge to the distal insertion of FDS
  • zone III:
    • from the distal edge of the carpal tunnel to the proximal end of the A1 pulley
    • contains the origin of lumbrical muscles that start from the FDP tendons
  • zone IV: within the carpal tunnel
  • zone V: from the musculotendinous junction in the forearm to the proximal aspect of the carpal tunnel

The thumb has its own zones 4:

  • zone TI: from flexor pollicis longus (FPL) insertion to A2 pulley
  • zone TII: from A2 pulley to distal A1 pulley
  • zone TIII: from distal A1 pulley to carpal tunnel

Practical points

  • zone II has been known as “no man’s land” due to the historical high complication rate 3,4

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