Extensor Tendon Injury Zones
Extensor tendon injuries are classified into eight zones [6].
Zone I is the area over the DIP joint and distal phalanx. Disruption of the tendon will cause mallet finger. The long-term consequence of this injury can be a swan-neck deformity.
Zone II is over the middle phalanx; assessment and treatment are the same as for zone I injuries.
Zone III is over the PIP joint. Injury here can result in a boutonnire’s deformity, which is hyperextension at the MCP and DIP joints.
Zone IV injuries are located on the proximal phalanx and are treated like zone III injuries.
Zone V injuries occur over the MCP joint.
Zone VI injuries are on the dorsum of the hand. The tendons are very superficial here and can be easily damaged.
Zone VII injuries involve the wrist and multiple tendons; these should be evaluated by a hand surgeon.
VIII
Zone VIII injuries are in the distal forearm. Injuries in this location often require tendon retrieval for complete lacerations and may need to be performed in the operating room.
Learning Bite
– The little finger FDS is absent in approximately 20% of individuals.
– Extensor zones can easily be recalled by remembering that the odd numbers overlie the joints.
– The thumb has no zone III since there is only one interphalangeal (IP) joint.