Lumbricals : Wheeless' Textbook of Orthopaedics

- 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