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Proximal interphalangeal joints of foot

The proximal interphalangeal (PIP) joints are the articulations between the heads of the proximal phalanges and the bases of the middle phalanges of the second to fifth toes. These are synovial hinge joints (ginglymus type) that allow primarily flexion and extension, contributing to toe balance, propulsion, and adaptability on uneven surfaces.

The great toe (hallux) lacks a PIP joint, having only a single interphalangeal joint. The PIP joints are stabilized by a fibrous joint capsule, collateral ligaments, and a plantar plate, which collectively provide stability and distribute mechanical loads during gait.

Synonyms

  • PIP joint of the toes

  • Proximal toe interphalangeal articulation

  • Phalangeal hinge joint of the foot

Location and Structure

  • Articulation: Between the head of each proximal phalanx and the base of the corresponding middle phalanx (2nd–5th toes).

  • Joint type: Synovial hinge joint with limited motion in other planes.

  • Capsule: Surrounds the joint, lined by synovium, and reinforced dorsally and laterally.

  • Cartilage: Articular surfaces are covered with hyaline cartilage ensuring smooth motion.

  • Range of motion: Approximately 35–45° flexion; minimal extension.

Relations

  • Dorsally: Extensor digitorum longus and brevis tendons

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

  • Laterally: Collateral ligaments

  • Proximally: Proximal phalanx head

  • Distally: Middle phalanx base

Ligamentous Attachments

  • Joint capsule: Thin and loose, enclosing the joint cavity.

  • Collateral ligaments: Thick cords on each side preventing excessive lateral deviation.

  • Plantar plate: Fibrocartilaginous thickening reinforcing the plantar capsule; provides attachment for flexor tendons.

  • Extensor apparatus: Merges dorsally with the capsule, aiding toe extension.

Nerve Supply

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

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

Function

  • Flexion and extension: Primary movements at the joint, essential for toe grip and propulsion.

  • Shock absorption: Distributes forces during weight bearing and push-off.

  • Joint stability: Collateral ligaments and plantar plate maintain toe alignment.

  • Assist in gait: Control fine toe movement and balance during stance phase.

Clinical Significance

  • Hammer toe deformity: Chronic flexion contracture at the PIP joint, common in tight footwear or imbalance.

  • Arthritis: Degenerative or inflammatory changes cause pain and stiffness.

  • Capsulitis: Overuse or trauma leads to joint capsule inflammation.

  • Fracture-dislocation: May occur with toe trauma or hyperextension.

  • Infection: Septic arthritis can result from penetrating injuries or adjacent ulceration.

  • Imaging relevance: MRI and CT provide precise evaluation of articular surfaces, ligaments, and deformities.

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark)

    • Marrow: Bright fatty signal in normal adults

    • Cartilage: Smooth, thin intermediate-to-low signal covering articular surfaces

    • Joint capsule and ligaments: Thin, low-signal lines

    • Pathology: Fractures appear as low-signal lines; edema or inflammation may cause intermediate-to-bright marrow change

  • T2-weighted images:

    • Cortex: Dark, low signal

    • Marrow: Bright signal due to fat and marrow content

    • Cartilage: Intermediate-to-bright; irregularities indicate chondral damage or thinning

    • Joint fluid: Hyperintense, outlining the joint space

    • Pathology: Bone marrow edema, synovitis, or effusion appear as hyperintense signals

  • STIR:

    • Normal marrow: Intermediate-to-dark signal intensity

    • Pathology: Bright hyperintense signal indicating marrow edema, contusion, or infection

    • Useful for early detection of inflammatory or traumatic changes

  • Proton Density Fat-Saturated (PD FS):

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

    • Abnormal findings: Bright hyperintensity from bone marrow edema, capsulitis, or ligamentous injury

    • Excellent for identifying subtle cartilage defects and joint effusions

  • T1 Fat-Sat Post-Contrast:

    • Normal joint: Mild homogeneous enhancement of synovium

    • Inflammatory arthritis: Diffuse synovial enhancement with joint effusion

    • Infection: Patchy marrow enhancement and pericapsular soft-tissue enhancement

    • Chronic degeneration: Minimal enhancement with possible synovial thickening

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, clearly defined

  • Trabecular bone: Fine, even pattern

  • Joint surface: Smooth and congruent; cartilage appears as a low-density interface

  • Pathology:

    • Detects fractures, erosions, sclerosis, or subluxation

    • Shows structural deformities such as hammer or claw toe alignment

    • Identifies osteophytes and joint narrowing in degenerative arthritis

Post-Contrast CT (standard):

  • Joint capsule and synovium: Enhancement in active inflammation or infection

  • Soft-tissue planes: Enhanced in septic arthritis, cellulitis, or capsulitis

  • Excellent for evaluating erosive arthropathy, post-traumatic changes, and joint fusion

MRI image

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

MRI image

Proximal interphalangeal joints of foot sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Proximal interphalangeal joints of foot ct coronal