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Second lumbrical muscle of foot

The second lumbrical muscle is one of the four small intrinsic muscles located in the second muscular layer of the sole of the foot. It plays a key role in coordinating toe flexion at the metatarsophalangeal (MTP) joints and extension at the interphalangeal (IP) joints, contributing to smooth toe movement and balance during gait.

The lumbricals act as fine-tuning muscles for foot stability and are particularly important in maintaining toe alignment and ground contact during walking and standing. The second lumbrical is unique because it receives dual innervation — from both the medial and lateral plantar nerves.

Synonyms

  • Second lumbrical of the foot

  • Medial lumbrical of the lateral three toes

Origin, Course, and Insertion

  • Origin: From the medial surface of the tendon of the flexor digitorum longus (FDL) corresponding to the second toe

  • Course: The slender muscle belly passes distally along the medial side of the second toe, superficial to the interossei, and crosses the plantar aspect of the MTP joint

  • Insertion: Onto the medial side of the dorsal digital expansion (extensor expansion) of the second toe, blending with tendons of the extensor digitorum longus and brevis

Tendon Attachments

  • The tendon attaches medially to the extensor expansion of the second toe

  • Works in coordination with the flexor digitorum longus and extensor digitorum longus tendons to balance toe movement

  • Stabilizes the MTP joint by preventing hyperextension during gait

Relations

  • Superiorly: Tendon of flexor digitorum longus

  • Inferiorly: Deep transverse metatarsal ligament and plantar aponeurosis

  • Medially: First lumbrical muscle

  • Laterally: Third lumbrical muscle

  • Posteriorly: Plantar vessels and nerves in the neurovascular plane

Nerve Supply

  • Dual innervation:

    • Medial plantar nerve (branch of tibial nerve, S1–S2) — for the first lumbrical and medial part of the second

    • Lateral plantar nerve (deep branch, S2–S3) — for the lateral part of the second lumbrical

Arterial Supply

  • Plantar metatarsal arteries (from deep plantar arch)

  • Contributions from medial and lateral plantar arteries

Venous Drainage

  • Plantar venous arch, draining into medial and lateral plantar veins, then into the posterior tibial vein

Function

  • Flexion at MTP joint: Flexes the proximal phalanx of the second toe

  • Extension at IP joints: Extends the middle and distal phalanges through the extensor expansion

  • Toe coordination: Assists in maintaining smooth toe-off and ground grip during walking

  • Balance and stability: Helps stabilize the digits, especially during propulsion in gait

Clinical Significance

  • Muscle imbalance: Weakness or paralysis can lead to claw toe deformity (hyperextension at MTP and flexion at IP joints)

  • Entrapment neuropathy: May occur due to medial or lateral plantar nerve compression

  • Injury or inflammation: Rare, but can occur secondary to overuse in dancers or runners

  • Post-surgical evaluation: Important landmark in forefoot surgeries and plantar nerve decompression

  • Imaging relevance: MRI helps assess intrinsic muscle atrophy, denervation, or fibrosis in neuropathic conditions

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity, small spindle-shaped belly between FDL and interossei

    • Surrounding fat planes: bright signal providing good contrast

    • Pathology (atrophy or denervation): increased T1 signal due to fatty infiltration

  • T2-weighted images:

    • Normal: intermediate-to-low signal, slightly darker than on T1

    • Tendon: low signal (dark line) along digit

    • Pathology: bright hyperintense signal in acute denervation, strain, or inflammation

    • Useful in detecting neuropathic or traumatic changes

  • STIR:

    • Normal muscle: intermediate-to-dark signal intensity

    • Pathology: bright hyperintense signal consistent with edema, inflammation, or acute neuropathy

    • Particularly sensitive for early denervation or fascial edema

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, homogeneous signal pattern

    • Pathologic: bright hyperintense foci indicating fluid or early muscle injury

    • Excellent for detecting subtle fascial or peritendinous edema in plantar neuropathies

  • T1 Fat-Sat Post-Contrast:

    • Normal: uniform mild enhancement

    • Pathology: increased enhancement in inflammatory myositis, neural entrapment, or postsurgical changes

    • Chronic denervation: minimal or absent enhancement, often with fatty replacement

CT Appearance

Non-Contrast CT:

  • Small soft-tissue structure between metatarsal bones and plantar fascia

  • Normal lumbrical blends with surrounding soft tissue; distinct fascial planes define its position

  • Fat infiltration in chronic neuropathy: low-attenuation changes within muscle belly

Post-Contrast CT (standard):

  • Normal muscle: homogeneous mild enhancement

  • Pathologic muscle (denervation or inflammation): patchy or diffuse enhancement

  • Adjacent neurovascular inflammation may also enhance in compressive neuropathies

MRI image

Second Lumbrical Muscle of Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

second Lumbrical Muscle of Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Second lumbrical muscle of Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

CT image

Second lumbrical muscle foot axial ct image