Ortho Oracle - orthopaedic operative atlas
Home » Bones » Hand » Lumbricals


- See:
      - Bunnel Test for Intrinsic Tightness:
      - Extensor Mechanism of Digits
      - Lumbrical Muscle Sheaths
      - Lumbical Plus Finger:

- Origin:
    - tendons of FDP tendon in center of palm, just proximal to the flexor sheath and the A1 pulley;
    - area of origin varies from 3.5 to 4 cm and extends from level of pisiform bone proximally;
    - lumbrical tendons pass volar to the deep transverse metacarpal ligament and insert into the radial lateral band of each finger;

- Insertion:
    - approaches the radial side of the metacarpal bone;
    - sends one slip dorsally into central slip;
    - sends another slip (called lateral band) which joins w/ lateral slip from EDC to form the lateral band;

- Discussion:
    - intrinsics  of hand are supplied by distal branches of ulnar and median  nerves;
    - hence, injury to both these nerves, esp ulnar nerve (distally), leads to imbalance between the extrinsic and intrinsic muscles;
    - lumbricals are prime flexors of MP joints;
    - they are responsible for well-synchronized flexion of MP joint w/ flexion of the interphalangeal (IP) joints;
    - lumbricals, further, in conjugation with the interossei, form that part of the extensor expansion that is chiefly responsible for extension of
            the proximal and distal interphalangeal joints;

Nerve supply:
   - 1st & 2nd lumbricals: median: C7 > C6;
   - 3rd & 4th lumbricals: ulnar: C8;

- Action:
    - when the lumbrical muscle contracts, it draws the lateral band proximally and  pulls the FDP distally (relaxing the tendon);
    - extends IP joints:
         - principal extensors of the interphalangeal joints (work horse);
         - extends the IP joint, irrespective of MCP joint postion;
         - facilitates IP extension by pulling profundi distally (unique ability to relax its on antagonist)
    - flexes MCP joint:
         - mainly in mechanical way by being pulled by the profundus;
         - Lumbricals are prime flexors of MP joints;
         - when MP joints are stabilized, lumbricals bend fingers toward thumb (index finger abduction, middle finger radial flexion, ring and little 
               finger adduction);
         - when fingers are flexed, lumbricals are pulled into carpal canal & recede proximally to the distal end of radius;
         - synergists: dorsal interossei,  palmar interossei, FDP, flexor digitorum superficialis

Movement patterns of interosseus-minus fingers.

Architectural design of the human intrinsic hand muscles.

Lumbrical function: interaction of lumbrical contraction with the elasticity the extrinsic finger muscles and its effect on metaphalangeal joint equilibrium.

A Biomechanical and Evolutionary Perspective on the Function of the Lumbrical Muscle