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Plantar interossei tendons of foot

The plantar interossei tendons are the distal tendinous continuations of the plantar interossei muscles, located in the fourth (deepest) layer of the sole of the foot. These muscles and tendons are crucial stabilizers of the metatarsophalangeal (MTP) joints and assist in adduction of the 3rd, 4th, and 5th toes toward the second toe, the midline of the foot.

Each plantar interosseous muscle arises from the medial aspect of the 3rd, 4th, and 5th metatarsal shafts, and transitions into a tendon that inserts onto the medial base of the proximal phalanx and extensor expansion of the same toe. The tendons contribute to toe adduction, flexion at the MTP joints, and extension at the interphalangeal joints, supporting coordinated digital movement during gait and balance.

Synonyms

  • Plantar interosseous tendons

  • Deep adductor tendons of the lateral toes

  • Medial interosseous tendons of foot

Origin, Course, and Insertion

  • Origin: Medial sides of the 3rd, 4th, and 5th metatarsal shafts

  • Course: The muscles pass anteriorly and distally in the sole, forming slender tendons that course beneath the deep transverse metatarsal ligament toward their respective toes

  • Insertion: Onto the medial aspect of the base of the proximal phalanges of the 3rd, 4th, and 5th toes and into the medial side of the extensor expansions

Tendon Attachments

  • Each plantar interosseous tendon blends with the flexor sheath and plantar plate at the MTP joint

  • Distally, the tendon merges with the extensor expansion of the corresponding toe

  • The arrangement provides dual action: flexion at the MTP joint and extension at the IP joints

  • Tendons run deep to the lumbricals and are aligned medially to the corresponding toe

Relations

  • Superiorly: Dorsal interossei muscles and deep plantar arch

  • Inferiorly: Plantar aponeurosis and lateral plantar vessels

  • Medially: Flexor tendons (FDL, FDB)

  • Laterally: Lateral plantar neurovascular bundle

  • Posteriorly: Quadratus plantae and deep plantar fascia

Nerve Supply

  • Lateral plantar nerve (branch of tibial nerve, roots S2–S3)

Function

  • Adduction: Draws the 3rd, 4th, and 5th toes medially toward the second toe (axis of foot)

  • Flexion: Aids flexion at the metatarsophalangeal joints

  • Extension: Assists extension of the interphalangeal joints via the extensor expansion

  • Arch support: Contributes to maintaining transverse arch stability

  • Dynamic balance: Provides fine control of toe positioning during locomotion and stance

Clinical Significance

  • Muscle imbalance: Weakness leads to splaying or abduction of lateral toes (seen in neuropathies or deformities)

  • Claw toe deformity: Overactivity or imbalance between interossei and long toe extensors/flexors

  • Entrapment neuropathy: Damage to lateral plantar nerve affects interossei strength and toe adduction

  • Atrophy detection: Seen in chronic tibial or sciatic neuropathies (visible on MRI)

  • Post-surgical relevance: Important in reconstructive procedures for toe deformities and metatarsalgia management

MRI Appearance

  • T1-weighted images:

    • Muscle bellies: intermediate signal intensity, clearly separated within the deep plantar layer

    • Tendons: low signal (dark linear structures) extending to bases of proximal phalanges

    • Intermuscular fat: bright, defining clear fascial boundaries

    • Chronic denervation: muscle shows fatty infiltration (high T1 signal)

  • T2-weighted images:

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

    • Normal tendons: very low signal (black)

    • Pathology: bright hyperintense signal in muscle (strain, edema, inflammation) or focal bright areas at tendon insertion (tendinopathy)

  • STIR:

    • Normal muscle: intermediate-to-dark signal intensity

    • Normal tendons: low (dark) signal

    • Pathologic: bright hyperintense changes indicating edema, partial tears, or inflammatory myositis

    • Sensitive for detecting subtle muscle denervation or early inflammation

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate-to-dark, uniform signal intensity

    • Normal tendons: low signal (dark)

    • Pathologic: bright focal regions in muscle or along tendon course, representing edema or partial-thickness injury

    • Excellent for distinguishing active myositis or fasciitis from chronic scarring

  • T1 Fat-Sat Post-Contrast:

    • Normal muscles: mild uniform enhancement

    • Inflamed tendons or fascia: show smooth, localized enhancement

    • Chronic fibrosis or denervation: non-enhancing central low-signal zones with peripheral enhancement

CT Appearance

Non-Contrast CT:

  • Muscles: fine soft-tissue structures in deep plantar layer

  • Tendons: seen as thin, linear soft-tissue densities extending to bases of toes

  • Interosseous spaces: clearly visible due to surrounding fat

  • Chronic pathology: may show atrophy, loss of bulk, or fibrotic density increase

Post-Contrast CT (standard):

  • Muscles: homogeneous mild enhancement

  • Inflamed tendon insertions or plantar fascia: focal enhancement

  • Useful for evaluating post-traumatic scarring, muscular atrophy, or calcific changes in interosseous compartment

MRI image

plantar interossei tendons of foot sfov of the Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000