Hand Lumbrical Muscles

The four slender hand lumbrical muscles were named because of their worm-like form (L. lumbricus, earthworm). They are short muscles of the hand alongside with the dorsal interossei and palmar interossei muscles.

The lumbricals flex the fingers at the metacarpophalangeal joints and extend the interphalangeal joints.

Hand Lumbrical Muscles Anatomy

The 1st hand lumbrical muscle originates from the radial side of the most radial tendon of the flexor digitorum profundus of the index finger, it passes posteriorly along the radial side of the index finger to insert on the extensor expansion near the metacarpophalangeal joint.

The 2nd lumbrical muscle originates from the radial side of the second most radial tendon of the flexor digitorum profundus (middle finger), it passes posteriorly along the radial side of the middle finger and inserts on the extensor expansion near the metacarpophalangeal joint.

See Also: Hand Anatomy, Bones & Muscles

The 3rd lumbrical muscle: one head originates on the radial side of the flexor digitorum profundus tendon of the ring finger, while the other head originates on the ulnar side of the tendon for the middle finger. The muscle passes posteriorly along the radial side of the ring finger to insert on its extensor expansion.

The 4th lumbrical muscle: one head originates on the radial side of the flexor digitorum profundus tendon corresponding to the little finger, while the other head originates on the ulnar side of the tendon for the ring finger. The muscle passes posteriorly along the radial side of the little finger to insert on its extensor expansion.

The first and second hand lumbrical muscles are supplied by the median nerve (C8-T1), while the third and fourth are supplied by the ulnar nerve (C8-T1).

These muscles get their blood supply from 4 separate source: the superficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital artery.

The hand lumbrical muscles have two different actions: flexion at the metacarpophalangeal joints and extension in both the proximal and distal interphalangeal joints.

To test the hand lumbrical muscles, with the palm facing superiorly, the patient is asked to flex the metacarpophalangeal (MP) joints while keeping the interphalangeal joints extended. The examiner uses one finger to apply resistance along the palmar surface of the proximal phalanx of digits 2–5 individually. Resistance may also be applied separately on the dorsal surface of the middle and distal phalanges of digits 2–5 to test extension of the interphalangeal joints, also while flexion of the MP joints is maintained.

References & More

1. Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.
2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
3. Valenzuela M, Launico MV, Varacallo M. Anatomy, Shoulder and Upper Limb, Hand Lumbrical Muscles. 2023 Nov 17. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 30521297. Pubmed
4. Palti R, Vigler M. Anatomy and function of lumbrical muscles. Hand Clin. 2012 Feb;28(1):13-7. doi: 10.1016/j.hcl.2011.09.002. Epub 2011 Oct 29. PMID: 22117920. Pubmed
5. Physiopedia – Lumbricals of the Hand
6. Clinically Oriented Anatomy – 8th Edition