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Updated: May 19 2021

Lumbrical Plus Finger

Images .jpg plus.jpg avulsion.jpg
  • Summary
    • Lumbrical Plus Finger is characterized by paradoxical extension of the IP joints while attempting to flex the fingers.
    • Diagnosis is made clinically with extension of the IP joints of one digit with attempted flexion of all fingers (making a fist).
    • Treatment is observation if patient is minimally symptomatic. Operative tenodesis of FDP to terminal tendon or lumbrical release is indicated if symptoms affect patient's activity demands.
  • Epidemiology
    • Anatomic location
      • most common in middle finger (2nd lumbrical)
        • FDP 3, 4, 5 share a common muscle belly
          • cannot independently flex 2 digits without pulling on the third
        • index finger has independent FDP belly
          • when making a fist following FDP2 transection, it is possible to only contract FDS2 (and not FDP2), thus avoiding paradoxical extension
  • Etiology
    • Pathophysiology
      • mechanism
        • FDP disruption distal to the origin of the lumbicals (most common)
          • can be due to
            • FDP transection
            • FDP avulsion
        • DIP amputation
        • amputation through middle phalanx shaft
        • "too long" tendon graft
      • pathoanatomy
        • lumbricals originate from FDP
        • with FDP laceration, FDP contraction leads to pull on lumbricals
        • lumbricals pull on lateral bands leading to PIP and DIP extension of involved digit
        • with the middle finger, when the FDP is cut distally, the FDP shifts ulnarly (because of the pull of the 3rd lumbrical origin)(bipennate)
          • this leads to tightening of the middle finger lumbrical (2nd lumbrical, unipennate), and amplifies the "lumbrical plus" effect
  • Anatomy
    • Lumbricals
      • 1st and 2nd lumbricals
        • unipennate
        • median nerve
        • originate from radial side of FDP2 and FDP3 respectively
      • 3rd and 4th lumbricals
        • bipennate
        • ulnar nerve
        • 3rd lumbrical originates from FDP 3 & 4
        • 4th lumbrical originates from FDP 4 & 5
      • all insert on radial side of extensor expansion
  • Presentation
    • History
      • recent volar digital laceration (FDP transection) or sudden axial traction on flexed digit (FDP avulsion)
    • Symptoms
      • notices that when attempting to grip an object or form a fist, 1 digit sticks out or gets caught on clothes
    • Physical exam
      • paradoxical IP extension with grip (fingers extend while holding a beer can)
  • Treatment
    • Operative
      • tenodesis of FDP to terminal tendon or reinsertion to distal phalanx
        • indications
          • FDP lacerations
          • do NOT suture flexor-extensor mechanisms over bone
      • lumbrical release
        • indications
          • if FDP is retracted or segmental loss makes it impossible to fix
          • NOT done in the acute setting as it does not occur consistently enough to warrant routine lumbrical sectioning acutely
        • contraindications
          • do not transect lumbricals 1 & 2 if there is concomitant ulnar nerve palsy
          • with ulnar nerve paralysis, the interosseous muscles are also lost
          • (interosseus muscles extend the IP joints)
        • technique
          • transect at base of flexor sheath (in the palm)
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