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Knot of Henry

The Knot of Henry (also known as the plantar crossover or chiasma plantare) is an important anatomical site in the sole of the foot where the tendons of the flexor hallucis longus (FHL) and flexor digitorum longus (FDL) intersect. It is located on the plantar aspect of the midfoot, typically beneath the navicular tuberosity and sustentaculum tali, in the deep layer of the sole.

This anatomical crossover allows the FHL and FDL to share mechanical force during toe flexion, ensuring coordinated movement and load transfer between the hallux and the lesser toes. However, because of its confined space and complex intertendinous connections, it is a common site of frictional irritation, adhesions, and entrapment syndromes, particularly in athletes and ballet dancers.

Synonyms

  • Plantar chiasm

  • Chiasma plantare

  • Master knot of Henry

Location and Structure

  • Situated in the deep plantar compartment, inferior to the talus and navicular, near the medial midfoot.

  • The flexor hallucis longus tendon runs from posterior to anterior and passes beneath the FDL tendon.

  • The flexor digitorum longus tendon crosses superficially over the FHL, forming a distinct X-shaped chiasm.

  • Intertendinous fibrous slips connect both tendons at this crossover point, allowing coordinated flexion.

  • Lies deep to the abductor hallucis and flexor digitorum brevis muscles.

Relations

  • Superiorly: Quadratus plantae and calcaneus

  • Inferiorly: FDL and FHL tendons with fibrous sheath

  • Medially: Abductor hallucis and tibialis posterior tendon

  • Laterally: Lateral plantar musculature

  • Anteriorly: Dividing FDL tendons to lateral toes

  • Posteriorly: FHL tendon approaching hallux

Clinical Significance

  • Knot of Henry syndrome: Tendinous entrapment or friction between FHL and FDL causing pain and restricted great toe motion

  • Overuse injuries: Common in runners, dancers, and athletes performing repetitive plantar flexion

  • Adhesions: Fibrous connections at the knot may lead to limited tendon gliding and “triggering” sensations

  • Post-surgical relevance: Important landmark in FHL tendon transfer and hallux surgery

  • Imaging importance: Critical for evaluating entrapment, synovitis, tenosynovitis, and post-traumatic adhesions

MRI Appearance

  • T1-weighted images:

    • FHL and FDL tendons: low signal (dark) linear structures crossing each other in an X-shaped configuration

    • Surrounding muscle: intermediate signal intensity

    • Fat planes around tendons appear bright and sharply defined

    • Adhesions or fibrosis: intermediate-to-low signal tissue between tendons

  • T2-weighted images:

    • Normal tendons: low signal (dark) continuous fibers

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

    • Pathology: hyperintense signal around or between tendons indicating fluid, edema, or synovial thickening

    • Adhesions appear as ill-defined intermediate bands bridging both tendons

  • STIR:

    • Normal muscles and tendons: intermediate-to-dark signal intensity

    • Pathology: bright hyperintense fluid or edema in peritendinous region

    • Excellent for detecting tenosynovitis, bursitis, or inflammatory changes around the crossover

  • Proton Density Fat-Saturated (PD FS):

    • Normal: tendons appear dark, surrounded by minimal fluid

    • Pathology: bright hyperintense fluid signal outlining the tendons or between them

    • Helps identify subtle peritendinous edema, adhesions, or chronic synovitis

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal enhancement

    • Inflamed or fibrotic tissue around the crossover: shows moderate-to-intense enhancement

    • Useful in distinguishing fibrosis (less enhancing) from active inflammation (strong enhancement)

CT Appearance

Non-Contrast CT:

  • FHL and FDL tendons: appear as soft-tissue density bands crossing in the deep plantar region

  • Adjacent muscles and fat planes distinguishable in high-resolution imaging

  • Chronic changes: may show thickened tendons or small calcific foci at the intersection site

Post-Contrast CT (standard):

  • Normal tendons: non-enhancing linear structures

  • Inflamed peritendinous tissues: show focal or diffuse enhancement

  • Helpful in assessing postoperative fibrosis, calcific tendinitis, or synovial proliferation

MRI image

Knot of Henry of the Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Knot of Henry of the Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Knot of Henry of the Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

CT image

Knot of Henry ct axial image