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Opponens digiti minimi muscle of foot

The opponens digiti minimi (ODM) of the foot is a small intrinsic muscle located in the third (deep) layer of the sole, forming part of the hypothenar group on the lateral side of the foot. It lies deep to the flexor digiti minimi brevis and superficial to the fifth metatarsal bone.

Although smaller and less developed than its hand counterpart, it assists in drawing the fifth metatarsal medially and slightly upward, thereby contributing to opposition and stabilization of the little toe during push-off and lateral balance. The ODM plays an important supportive role in maintaining the lateral longitudinal arch of the foot.

Synonyms

  • Opponens of the little toe

  • Opponens digiti quinti (pedis)

  • Deep flexor of the fifth metatarsal

Origin, Course, and Insertion

  • Origin: Long plantar ligament and base of the fifth metatarsal bone

  • Course: Short, flat muscular belly extending obliquely along the lateral plantar surface of the fifth metatarsal

  • Insertion: Entire length of the lateral and plantar aspect of the fifth metatarsal shaft

Tendon Attachments

  • The ODM muscle typically has no separate tendon, as it inserts directly onto the bone.

  • Occasionally, fibers merge with the flexor digiti minimi brevis tendon or the abductor digiti minimi for added stability of the fifth ray.

Relations

  • Superiorly: Fifth metatarsal bone

  • Inferiorly: Plantar aponeurosis

  • Medially: Flexor digiti minimi brevis

  • Laterally: Abductor digiti minimi

  • Posteriorly: Lateral plantar nerve and vessels

  • Anteriorly: Tendon sheath of the fifth toe

Nerve Supply

  • Lateral plantar nerve, deep branch (S2–S3), a branch of the tibial nerve

Arterial Supply

  • Lateral plantar artery, with contributions from the arcuate artery and plantar metatarsal arteries

Venous Drainage

  • Lateral plantar vein and accompanying venous plexus draining into the posterior tibial vein

Function

  • Opposition of fifth metatarsal: Pulls the fifth metatarsal medially and slightly upward, aiding in toe opposition

  • Lateral arch support: Maintains and stabilizes the lateral longitudinal arch of the foot

  • Assists in abduction and flexion: Works synergistically with abductor and flexor digiti minimi muscles

  • Dynamic stabilization: Provides balance during gait, particularly in uneven terrain or side-to-side movements

Clinical Significance

  • Muscle atrophy: Seen in chronic lateral plantar nerve compression (Baxter’s neuropathy)

  • Strain or spasm: May contribute to lateral foot pain and arch imbalance

  • Nerve entrapment: Deep branch of the lateral plantar nerve injury may weaken ODM function

  • Surgical relevance: Important landmark in lateral plantar surgical approaches

  • Imaging importance: MRI helps assess denervation, tears, or atrophy of small intrinsic muscles of the foot

MRI Appearance

  • T1-weighted images:

    • Muscle belly: intermediate signal intensity, easily distinguished from surrounding bright fat

    • Normal fascicular pattern preserved

    • Fat infiltration (in chronic denervation): areas of high signal intensity

    • Adjacent bone cortex (fifth metatarsal) appears as low signal

  • T2-weighted images:

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

    • Pathology: bright hyperintense regions indicating strain, tear, or edema

    • Chronic atrophy: overall volume loss with fat replacement (increased signal on T1, decreased on T2)

  • STIR:

    • Normal ODM: intermediate-to-dark signal

    • Pathology: bright hyperintensity in acute edema, inflammation, or muscle tear

    • Denervation changes appear as patchy hyperintensity in the acute phase

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark homogeneous muscle signal

    • Abnormal: focal bright hyperintense signal within muscle belly (strain, edema, or partial tear)

    • Subtle perimuscular fluid or nerve inflammation can be well visualized

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: mild uniform enhancement

    • Inflammation or myositis: focal or diffuse enhancement

    • Chronic denervation or fibrosis: minimal or peripheral enhancement with low-signal fibrotic core

CT Appearance

Non-Contrast CT:

  • Muscle: soft-tissue density along lateral plantar aspect of fifth metatarsal

  • Differentiated from plantar fascia and adjacent muscles by its location

  • Bone changes such as periosteal reaction or sclerosis may indicate chronic stress at the insertion

Post-Contrast CT (standard):

  • Muscle: uniform enhancement

  • Inflamed or hypertrophic ODM may show localized enhancement

  • Useful in evaluating calcifications, ossifications, or post-traumatic fibrosis in the lateral midfoot

MRI images

opponens digiti minimi muscle of foot axialcross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

opponens digiti minimi muscle of foot coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI images

opponens digiti minimi muscle of foot sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

opponens digiti minimi muscle of foot ct axial