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Base of the phalanx (hand)

The base of the phalanx is the proximal articular end of each phalangeal bone in the fingers. It articulates with the head of the preceding bone—that is, the metacarpal head for proximal phalanges, and the head of the proximal or middle phalanx for middle and distal phalanges. Together, these articulations form the metacarpophalangeal (MCP) and interphalangeal (IP) joints of the hand.

The base provides a stable articular platform for flexion and extension movements and serves as an anchoring site for tendons, capsules, and ligaments essential for fine motor control, grip strength, and joint stability.

Synonyms

  • Proximal articular end of the phalanx

  • Phalangeal base

  • Phalangeal proximal extremity

Location and Structure

  • The base of the phalanx forms the expanded proximal portion of each phalangeal bone.

  • Proximal phalanges: Bases articulate with metacarpal heads at the MCP joints.

  • Middle phalanges: Bases articulate with the heads of the proximal phalanges.

  • Distal phalanges: Their bases articulate with the heads of the middle phalanges (in digits 2–5).

  • Articular surface: Concave and covered with hyaline cartilage for smooth movement.

  • The dorsal surface gives attachment to the extensor apparatus, while the palmar surface supports the fibrous digital sheath and volar plate.

Relations

  • Dorsally: Extensor tendon expansions (extensor digitorum and intrinsic tendons)

  • Palmarly: Volar plate and flexor tendons (flexor digitorum superficialis and profundus)

  • Laterally: Collateral ligaments of MCP or IP joints

  • Proximally: Head of preceding bone (metacarpal or proximal phalanx)

  • Distally: Shaft of the same phalanx

Attachments

  • Joint capsule: Surrounds the articular margins, strengthened by collateral ligaments on each side.

  • Tendons:

    • Dorsal aspect: Insertion of extensor digitorum, extensor indicis, or extensor digiti minimi tendons via extensor expansion.

    • Palmar aspect: Passage of flexor tendons beneath the fibrous flexor sheath.

  • Ligaments:

    • Collateral ligaments attach along the lateral aspects of the base.

    • The volar plate attaches to the palmar lip of the base, resisting hyperextension.

Arterial Supply

  • Digital branches from the proper palmar digital arteries (from the superficial palmar arch).

  • Additional contribution from dorsal digital arteries (from dorsal metacarpal arteries).

Function

  • Joint articulation: Forms part of MCP or IP joints, enabling flexion, extension, and fine control.

  • Load transmission: Transfers forces between phalanges and metacarpals during grasp and manipulation.

  • Stabilization: Serves as attachment for capsules and ligaments maintaining digital joint integrity.

  • Tendon anchorage: Provides insertion points for flexor and extensor apparatus, critical for coordinated finger motion.

Clinical Significance

  • Fractures: Common at the base of proximal phalanges due to direct trauma or hyperextension (e.g., ball-handling sports).

  • Avulsion injuries: May involve collateral ligaments or volar plate.

  • Dislocations: MCP or PIP dislocations often associated with capsuloligamentous tears.

  • Arthritis: Degenerative, inflammatory, or post-traumatic changes may cause joint pain or stiffness.

  • Osteomyelitis: Can result from penetrating trauma or local infection spread.

  • Imaging relevance: Essential for evaluating fractures, alignment, cartilage wear, or tendon insertion abnormalities.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark).

    • Bone marrow: Bright signal (fatty marrow).

    • Articular cartilage: Thin, smooth intermediate-to-low signal surface.

    • Joint capsule: Low signal outlining the joint margins.

    • Fracture lines: Linear low-signal defects crossing cortex or subchondral bone.

  • T2-weighted images:

    • Cortex: Low signal.

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

    • Cartilage: Intermediate-to-bright, smoothly curving over articular surface.

    • Joint fluid: Hyperintense, accentuating the joint contour.

    • Pathology: Bone contusion and marrow edema appear hyperintense; arthritis shows cartilage irregularity.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal.

    • Pathologic marrow: Bright hyperintense in edema, infection, or fracture.

    • Highlights subtle stress injuries, early osteomyelitis, or inflammatory changes.

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark signal.

    • Pathologic: Focal bright hyperintensity in marrow or adjacent soft tissue (indicative of edema or tenosynovitis).

    • Excellent for visualizing ligamentous injuries, cartilage wear, and capsular thickening.

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Mild homogeneous enhancement.

    • Synovitis or inflammation: Enhancing synovial lining or pericapsular soft tissue.

    • Osteomyelitis: Patchy, irregular marrow enhancement with cortical involvement.

    • Arthritis: Diffuse synovial enhancement, possibly with joint effusion.

CT Appearance

Non-Contrast CT:

  • Cortex: High-attenuation, sharply defined bone outline.

  • Trabecular bone: Fine, uniform honeycomb texture.

  • Articular surface: Smooth and concave; cartilage appears as a low-density interface.

  • Pathology: Excellent for detecting fractures, subchondral sclerosis, osteophytes, or erosions.

  • Use: Ideal for preoperative planning and post-traumatic alignment assessment.

MRI images

Base of the Phalanx of the Hand axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Base of the Phalanx of the Hand coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Base of the Phalanx of the Hand coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Base of the Phalanx of the Hand coronal ct image

CT image

Base of the Phalanx of the Hand ct sag image