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Interphalangeal joint of great toe

The interphalangeal joint of the great toe (hallux IP joint) is a synovial hinge joint formed between the head of the proximal phalanx and the base of the distal phalanx of the hallux. It allows primarily flexion and extension, contributing to toe-off stability during gait.

This joint is structurally similar to the interphalangeal joints of the lesser toes but is larger and stronger, reflecting its weight-bearing function. The IP joint is supported by a strong capsule, robust collateral ligaments, and a thick plantar plate, all of which ensure joint congruity and stability under load.

Synonyms

  • Hallux interphalangeal joint (Hallux IPJ)

  • Great toe IP joint

  • Interphalangeal articulation of the hallux

Location and Structure

  • Articulation: Between the head of the proximal phalanx and the base of the distal phalanx of the great toe.

  • Type: Synovial hinge joint (ginglymus), allowing mainly flexion with limited extension.

  • Capsule: Fibrous, attached to the margins of the articular surfaces and strengthened by ligaments.

  • Cartilage: Both articular surfaces are covered with hyaline cartilage, ensuring smooth gliding movement.

  • Plantar plate: Thick fibrocartilaginous plate reinforcing the plantar surface, preventing hyperextension.

  • Synovial membrane: Lines the inner surface of the capsule and secretes synovial fluid.

Relations

  • Dorsally: Tendon of extensor hallucis longus (EHL)

  • Plantar aspect: Tendon of flexor hallucis longus (FHL) and the thick plantar plate

  • Laterally: Collateral ligaments providing lateral stability

  • Proximally: Head of proximal phalanx

  • Distally: Base of distal phalanx

Ligamentous Attachments

  • Capsule: Encloses the joint and is lined by synovium

  • Collateral ligaments: Strong cords on either side; prevent lateral displacement and excessive extension

  • Plantar plate: Thick fibrocartilaginous structure reinforcing the plantar capsule and resisting hyperextension

  • Extensor expansion: Dorsal thickening formed by the EHL tendon blending with the capsule

Nerve Supply

  • Plantar aspect: Digital branch of the medial plantar nerve (from the tibial nerve)

  • Dorsal aspect: Dorsal digital branch of the deep fibular (peroneal) nerve

Function

  • Flexion and extension: Enables downward and upward motion of the great toe at the IP joint

  • Load transmission: Assists during push-off phase of gait, especially in propulsion

  • Stability: Plantar plate and collateral ligaments maintain joint alignment during movement

  • Shock absorption: Cartilage cushions impact forces during weight bearing

Clinical Significance

  • Arthritis: Osteoarthritis or post-traumatic arthritis common due to repetitive stress or hallux rigidus progression

  • Fractures: May involve articular surfaces of the proximal or distal phalanx head/base

  • Capsulitis or synovitis: Inflammation from overuse or abnormal load distribution

  • Sesamoid influence: Altered biomechanics secondary to sesamoid pathology may stress the IP joint

  • Tendon injury: EHL or FHL tendinopathy or rupture affects joint motion and stability

  • Infection: May occur as septic arthritis from penetrating injuries or ulcer extension

  • Post-surgical evaluation: Important in hallux valgus and interphalangeal arthrodesis imaging

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark)

    • Bone marrow: Bright, fatty marrow signal in both phalanges

    • Articular cartilage: Smooth intermediate-to-low signal layer over joint surfaces

    • Capsule and ligaments: Low-signal linear structures outlining the joint

    • Fracture or erosion: Appears as focal low-signal line through subchondral bone

  • T2-weighted images:

    • Cortex: Low signal

    • Marrow: Bright, slightly less than T1

    • Cartilage: Intermediate-to-bright, sharply defined

    • Joint fluid: Hyperintense, highlighting articular margins

    • Pathology: Synovitis, effusion, or marrow edema appear as high-signal foci

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Abnormal marrow: Bright hyperintense in edema, fracture, or infection

    • Sensitive for early detection of stress changes or osteitis

  • Proton Density Fat-Saturated (PD FS):

    • Normal joint and marrow: Intermediate-to-dark signal

    • Pathology: Bright hyperintense regions in marrow, capsule, or ligaments (edema, inflammation, or tear)

    • Highlights joint effusion, cartilage loss, and subtle bone marrow changes

  • T1 Fat-Sat Post-Contrast:

    • Normal joint: Mild homogeneous synovial enhancement

    • Synovitis: Diffuse or nodular enhancing synovial thickening

    • Osteomyelitis: Patchy enhancement within marrow with cortical breach

    • Septic arthritis: Enhancing capsule and pericapsular soft tissue

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, smooth and sharply defined

  • Trabecular bone: Fine, regular pattern within phalanges

  • Articular surfaces: Smooth; cartilage not directly visible but joint space preserved

  • Pathology: Detects fractures, erosions, subchondral sclerosis, and small osteophytes

  • Alignment: Evaluates joint congruity and subluxations post-trauma or surgery

Post-Contrast CT (standard):

  • Capsule and soft tissues: Enhancement in inflammatory or infectious conditions

  • Joint margins: May enhance mildly in synovitis or arthropathy

  • Particularly useful for evaluating degenerative changes, fractures, and septic arthritis

MRI image

Interphalangeal joint of great toe of foot coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Interphalangeal joint of great toe ct coronal image

CT VRT 3D image

Interphalangeal joint of great toe 3d image