The zone of flexor tendon injury that carries the poorest prognosis following injury and repair is:

B. Zone II.

DISCUSSION: Zone I extends from the distal margin of the flexor digitorum superficialis insertion to the flexor digitorum profundus insertion. Injury at this level involves only the profundus tendon. Zone II is defined as the proximal edge of the first annular pulley to the distal margin of the flexor digitorum superficialis insertion. At this level both the superficialis and profundus tendons are contained in a rigid fibroosseous canal. The smooth gliding required at the interfaces at this level may be compromised by adhesions following injury, thus making this the level with the poorest functional prognosis after injury. Injuries in Zones III, IV, and V, at the level of the palm, carpal canal, and distal forearm, respectively, may injure both or either of the flexor tendons to a digit. However, because of a less constrictive environment at the levels, adhesions that limit motion are less likely and the prognosis better than with Zone II injuries.