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Middle phalanx of hand

The middle phalanx of the hand is the intermediate bone of the digits (index, middle, ring, and little fingers). It lies between the proximal and distal phalanges, forming the proximal interphalangeal (PIP) joint proximally and the distal interphalangeal (DIP) joint distally. The thumb lacks a middle phalanx, having only proximal and distal segments.

Structurally, the middle phalanx is a small, tubular long bone with a base, shaft, and head. Its configuration allows fine digital movement and precision grip, while providing strength for flexion and extension during grasp and manipulation.

Synonyms

  • Intermediate phalanx of the hand

  • Middle digital bone

  • Second phalanx of the finger

Location and Structure

  • Location: Situated between the proximal and distal phalanges of the second to fifth digits.

  • Shape: Shorter and smaller than the proximal phalanx, with a concave base, cylindrical shaft, and condylar head.

  • Articulations:

    • Proximally: With the head of the proximal phalanx (forming the PIP joint).

    • Distally: With the base of the distal phalanx (forming the DIP joint).

  • Cortex: Thick compact bone surrounding a central cancellous core containing bone marrow.

  • Surface features: Flexor and extensor tendon attachments at the base and dorsal surface.

Relations

  • Dorsally: Extensor digitorum and extensor indicis tendons (depending on the finger).

  • Ventrally: Flexor digitorum superficialis (inserts at base) and flexor digitorum profundus tendons (pass distally).

  • Laterally: Collateral ligaments of interphalangeal joints.

  • Proximally: Head of proximal phalanx.

  • Distally: Base of distal phalanx.

Attachments

  • Flexor digitorum superficialis (FDS): Inserts onto the sides of the shaft of the middle phalanx, allowing finger flexion at the PIP joint.

  • Extensor expansion: Inserts onto the dorsal base, enabling extension.

  • Collateral ligaments: Attach along lateral surfaces, reinforcing the PIP and DIP joints.

  • Joint capsules: Enclose both interphalangeal joints.

Nerve Supply

  • Digital branches of the median and ulnar nerves provide sensory innervation to the periosteum and surrounding joint capsule.

Function

  • Flexion and extension: Primary movement at PIP and DIP joints for grasp and release.

  • Force transmission: Transfers mechanical load between proximal and distal phalanges.

  • Grip strength: Contributes to fine digital control and stability during pinch or precision tasks.

  • Balance: Maintains digital alignment and coordination.

Clinical Significance

  • Fractures: Common from direct trauma, crush injuries, or hyperextension; classified as shaft, base, or condylar fractures.

  • Dislocations: Usually involve the PIP joint; may be associated with collateral ligament rupture.

  • Osteoarthritis: Degeneration at interphalangeal joints with cartilage loss and osteophyte formation.

  • Osteomyelitis: Infection following trauma or hematogenous spread.

  • Mallet finger deformity: Involves distal phalanx but may extend into middle phalanx via extensor tendon disruption.

  • Imaging importance: MRI and CT used to assess fractures, marrow pathology, ligamentous injury, or arthritis.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark).

    • Bone marrow: Bright due to fatty content in adults.

    • Articular cartilage: Smooth thin intermediate-to-low signal on articular ends.

    • Joint capsule and ligaments: Low-signal linear structures.

    • Pathology: Fractures show linear low-signal lines; marrow edema appears intermediate-to-bright.

  • T2-weighted images:

    • Cortex: Low signal.

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

    • Cartilage: Intermediate-to-bright; irregularity indicates degeneration or chondral defect.

    • Joint fluid: Bright hyperintense, highlighting PIP or DIP joint space.

    • Pathology: Bone contusion or edema appears as hyperintense foci within marrow.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal.

    • Abnormal marrow: Bright hyperintensity in edema, infection, or stress fracture.

    • Detects early inflammatory changes or subtle bone injury not visible on radiographs.

  • Proton Density Fat-Saturated (PD FS):

    • Normal bone marrow: Intermediate-to-dark.

    • Abnormal: Bright hyperintense signal in marrow or soft tissue (edema, capsulitis, or tendon injury).

    • Ideal for assessing ligament tears, joint effusion, and subtle trabecular microfractures.

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Homogeneous mild enhancement.

    • Inflammatory or infective change: Patchy or diffuse marrow enhancement.

    • Synovitis or arthritis: Enhancing joint capsule and pericapsular soft tissue.

    • Osteomyelitis: Irregular marrow enhancement with cortical involvement.

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation with crisp margins.

  • Trabecular bone: Fine reticular pattern.

  • Articular surfaces: Smooth and well-defined; cartilage appears as thin low-density layer.

  • Fractures: Seen as lucent lines or cortical discontinuity; may show minimal displacement.

  • Degeneration: Subchondral sclerosis, cysts, or osteophytes.

  • Calcifications: Within tendons or capsule may be visible in chronic inflammation.

MRI images

middle phalanx of hand coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

middle phalanx of hand CORONAL CT IMAGE 1

CT image

middle phalanx of hand CORONAL CT IMAGE 2

CT image

middle phalanx of hand sagittal CT image