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



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, January 2, 2014 10:24 am