Lumbrical Plus Finger

Topic updated on 07/03/16 1:45am
  • Characterized by paradoxical extension of the IP joints while attempting to flex the fingers
  • Epidemiology
    • 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
  • 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
  • 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
  • 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  post
    • paradoxical IP extension with grip (fingers extend while holding a beer can) 
  • 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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Qbank (1 Questions)

(OBQ08.61) What is a potential complication of an amputation at the level of the distal interphalangeal joint? Topic Review Topic

1. Central slip rupture
2. Swan neck deformity
3. Boutonniere deformity
4. Lumbrical plus finger
5. Quadrigia effect



Demonstrates a lumbrical plus after flexor tendon laceration. When the FDP is l...
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