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Fifth metacarpal bone (metacarpal V)

The fifth metacarpal bone (metacarpal V) is the most medial metacarpal of the hand, corresponding to the little finger. It articulates proximally with the hamate bone, laterally with the fourth metacarpal, and distally with the proximal phalanx of the little finger.
It plays a critical role in hand grip, ulnar border stability, and power grasping movements. The bone’s distinct morphology and relatively high mobility make it prone to fractures, particularly the boxer’s fracture at its neck.

Synonyms

  • Fifth metacarpal

  • Little finger metacarpal

  • Ulnar metacarpal

Location and Structure

  • Position: Located on the ulnar (medial) side of the hand, forming the bony framework of the fifth ray.

  • Length: Shorter than the second to fourth metacarpals, but longer than the first.

  • Shape: Long bone with a base, shaft, and head.

  • Base: Expanded proximal end that articulates with the hamate and fourth metacarpal.

  • Shaft: Slightly curved, with a dorsal convexity and palmar concavity.

  • Head: Rounded distal articular surface for the proximal phalanx of the little finger.

  • Tubercle: Small projection on the lateral base serving for ligamentous attachment.

Articulations

  • Proximal articulation: With the hamate bone at the carpometacarpal (CMC) joint.

  • Medial articulation: None.

  • Lateral articulation: With the fourth metacarpal through an intermetacarpal joint.

  • Distal articulation: With the base of the proximal phalanx of the fifth digit.

Attachments

  • Muscular:

    • Flexor carpi ulnaris: Inserts at the base (via the pisometacarpal ligament).

    • Opponens digiti minimi: Inserts along the ulnar border of the shaft.

    • Interossei muscles: Attach on its lateral surfaces (palmar and dorsal interossei).

  • Ligamentous:

    • Dorsal and palmar carpometacarpal ligaments.

    • Intermetacarpal ligaments connecting to the fourth metacarpal.

    • Collateral ligaments of the metacarpophalangeal (MCP) joint distally.

Relations

  • Dorsally: Extensor tendons of the little finger (extensor digiti minimi, extensor digitorum).

  • Palmarly: Flexor tendons (flexor digitorum profundus and superficialis).

  • Medially: Hypothenar muscles and ulnar neurovascular bundle.

  • Laterally: Fourth metacarpal bone and interosseous spaces.

Function

  • Hand mobility: Provides axial support for the little finger during flexion and opposition.

  • Grip strength: Aids in power grasp and cupping motion of the palm.

  • Force distribution: Transfers load from the ulnar hand border to the carpal bones.

  • Articulation: Contributes to flexibility and ulnar deviation of the hand.

Clinical Significance

  • Boxer’s fracture: Common fracture through the neck of the fifth metacarpal after a closed-fist impact.

  • Base fractures: May involve carpometacarpal joint, often associated with hamate fractures.

  • Dislocation: Carpometacarpal or metacarpophalangeal dislocations occur in high-energy trauma.

  • Osteoarthritis: Degenerative change may affect the fifth CMC or MCP joints.

  • Surgical relevance: Base used as fixation site in hand reconstructive surgery or bone grafting.

  • Imaging importance: Essential for evaluation of alignment, angulation, and articular integrity.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark).

    • Bone marrow: Bright fatty signal, especially in adults.

    • Cartilage at articulations: Intermediate-to-low signal, smooth and uniform.

    • Soft tissues and tendons: Low signal, surrounded by bright subcutaneous fat.

    • Fractures or bone contusions: Appear as linear or patchy low-signal areas crossing cortex and marrow.

  • T2-weighted images:

    • Cortex: Low signal.

    • Marrow: Bright (fatty marrow with mild water component).

    • Articular cartilage: Intermediate-to-bright signal at joint surfaces.

    • Pathology: Marrow edema or subacute fracture shows hyperintense signal; cortical disruption evident.

    • Surrounding soft tissues: Fluid or edema appears bright.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal.

    • Pathology: Bright hyperintense areas represent edema, contusion, or osteomyelitis.

    • Sensitive for early detection of stress injury, inflammation, or infection.

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark, homogeneous signal.

    • Abnormal: Bright hyperintense foci indicating marrow edema or inflammation.

    • Excellent for subtle periosteal reaction, ligament injury, or soft-tissue swelling.

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Mild homogeneous enhancement of marrow.

    • Infection or inflammation: Patchy, irregular enhancement with cortical involvement.

    • Tumor or metastasis: Nodular or heterogeneous enhancement pattern.

    • Fracture healing: Linear peripheral enhancement at callus formation sites.

CT Appearance

Non-Contrast CT:

  • Cortex: High-attenuation dense margin, sharply outlined.

  • Trabecular bone: Fine lattice-like internal pattern.

  • Articular surfaces: Smooth and well-defined at both base and head.

  • Pathology:

    • Fractures, cortical breaks, and angulation easily identified.

    • Detects sclerosis, osteophytes, and degenerative changes in CMC or MCP joints.

    • Demonstrates post-traumatic deformities or callus formation with precision.

CT VRT 3D image

Metacarpal V (5th) bone bone CT 3D VRT image -img-00000-00000

MRI image

fifth metacarpal bone (metacarpal V) AXIAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

fifth metacarpal bone (metacarpal V) coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Metacarpal V (5th) ct coronal image