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Distal interphalangeal joint of foot

The distal interphalangeal (DIP) joint of the foot is the articulation between the head of the middle phalanx and the base of the distal phalanx in the second to fifth toes. It is a synovial hinge joint, allowing mainly flexion and extension, and stabilized by a robust fibrous capsule, collateral ligaments, and a thick plantar plate.

The joint provides fine digital motion, assists in load distribution, and maintains toe alignment during gait and balance. Its structure is similar to the proximal interphalangeal joint but smaller and less mobile. The great toe (hallux) lacks a DIP joint, as it has only one interphalangeal joint.

Synonyms

  • DIP joint of the toe

  • Distal phalangeal joint

  • Toe interphalangeal articulation

Location and Structure

  • Articulation: Between the head of the middle phalanx and base of the distal phalanx (second to fifth toes).

  • Type: Synovial hinge joint (ginglymus).

  • Capsule: Fibrous capsule surrounds the joint, lined with synovium and strengthened by ligaments.

  • Cartilage: Articular surfaces covered by hyaline cartilage ensuring smooth movement.

  • Joint cavity: Small, containing synovial fluid for lubrication.

  • Motion range: Approximately 30–50° flexion, limited extension.

Relations

  • Dorsally: Extensor digitorum longus and brevis tendons

  • Plantar aspect: Flexor digitorum longus and brevis tendons, plantar plate

  • Laterally: Collateral ligaments

  • Proximally: Middle phalanx

  • Distally: Distal phalanx and nail bed region

Ligamentous Attachments

  • Capsule: Encloses the joint, reinforced dorsally and laterally.

  • Collateral ligaments: Strong bands on both sides, preventing lateral displacement and overextension.

  • Plantar plate: Fibrocartilaginous structure reinforcing the plantar surface, providing load-bearing stability.

  • Extensor tendon expansion: Merges with dorsal capsule to assist in extension of the distal phalanx.

Nerve Supply

  • Digital branches of the medial and lateral plantar nerves (from tibial nerve).

  • Dorsal digital branches of the deep fibular nerve supply the dorsal aspect.

Function

  • Flexion and extension: Enables toe flexion during push-off and extension during swing phase.

  • Load distribution: Assists in shock absorption and even pressure transfer across distal phalanges.

  • Fine balance control: Maintains toe stability during standing and locomotion.

  • Protection: Plantar plate resists hyperextension and distributes mechanical stress.

Clinical Significance

  • Arthritis: Degenerative changes or post-traumatic arthritis cause stiffness and pain.

  • Capsulitis: Inflammation of joint capsule due to repetitive trauma or overuse.

  • Mallet toe deformity: Results from rupture or attenuation of the extensor tendon at DIP joint.

  • Fracture-dislocation: Common in sports and crush injuries involving distal phalanx.

  • Infection: May extend from distal ulcers or paronychia to involve joint (septic arthritis).

  • Imaging importance: MRI and CT crucial for assessing joint alignment, cartilage integrity, and soft-tissue pathology.

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark)

    • Marrow: Bright, fatty signal in normal adults

    • Articular cartilage: Smooth, thin intermediate-to-low signal covering joint surfaces

    • Joint capsule and ligaments: Thin low-signal bands

    • Pathology: Fractures appear as low-signal lines; marrow edema is intermediate-to-bright

  • T2-weighted images:

    • Cortex: Low signal

    • Marrow: Bright, slightly less intense than fat on T1

    • Cartilage: Intermediate-to-bright; irregularity indicates degeneration or erosion

    • Joint fluid: Hyperintense, outlining articular surfaces

    • Pathology: Effusion, synovitis, or bone contusions appear bright

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Pathology: Bright hyperintense signal with indistinct trabecular margins in edema, infection, or osteitis

    • Excellent for detecting early inflammatory and traumatic bone changes

  • Proton Density Fat-Saturated (PD FS):

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

    • Abnormal: Bright hyperintense regions in bone marrow or soft tissues (edema, capsulitis, or tendon injury)

    • Highlights subtle cartilage defects and joint effusion

  • T1 Fat-Sat Post-Contrast:

    • Normal joint: Mild homogeneous enhancement of synovium

    • Inflammatory arthritis: Diffuse synovial enhancement

    • Osteomyelitis or infection: Patchy marrow enhancement with cortical irregularity

    • Septic arthritis: Enhancing capsule and pericapsular soft tissue

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation with sharply defined margins

  • Trabecular bone: Uniform fine pattern

  • Articular surface: Smooth convex head of middle phalanx and concave base of distal phalanx

  • Pathology:

    • Detects fractures, erosions, subchondral sclerosis, or small osteophytes

    • Demonstrates mallet toe deformities or dislocations

    • Excellent for preoperative joint assessment

Post-Contrast CT (standard):

  • Joint capsule and synovium: Enhancing in inflammation or infection

  • Soft-tissue changes: Pericapsular enhancement in arthritis or septic conditions

  • Useful for evaluating chronic degenerative joint disease, trauma, and osteomyelitis

MRI image

Distal interphalangeal joint of foot coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Distal interphalangeal joint of foot SAG cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Distal interphalangeal joint of foot CT axial

CT VRT 3D image

Distal interphalangeal joint of foot 3D IMAGE