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Base of metacarpal bone

The base of the metacarpal bone forms the proximal end of each metacarpal in the hand and articulates with the distal row of carpal bones to form the carpometacarpal (CMC) joints. Each base varies slightly in shape, size, and articulation depending on its position in the hand, reflecting the functional differences between the thumb and fingers.

The first metacarpal base articulates with the trapezium and allows a wide range of motion (saddle joint), while the second to fifth bases articulate with the trapezoid, capitate, and hamate, forming plane-type joints that permit only limited gliding movements. These joints provide both stability and flexibility essential for gripping, precision, and manipulation.

Synonyms

  • Proximal end of the metacarpal

  • Carpometacarpal base

  • Metacarpal proximal articulation

Location and Structure

  • Position: Proximal extremity of the metacarpal, articulating with corresponding carpal bones.

  • Shape: Flattened or irregular to fit the carpal articular surface; broader dorsally than palmarly.

  • Articular surface: Covered by hyaline cartilage, smooth and concave or convex depending on the metacarpal.

  • Periosteum: Encloses the non-articular areas, providing attachment to ligaments and tendons.

  • Adjacent joints: Second to fifth metacarpals articulate laterally with one another through small articular facets, enhancing stability of the hand arch.

Relations

  • Proximally: Carpal bones (trapezium, trapezoid, capitate, hamate)

  • Distally: Shaft of the metacarpal bone

  • Dorsally: Extensor tendons and dorsal carpometacarpal ligaments

  • Palmarly: Palmar carpometacarpal ligaments, interosseous muscles, and flexor tendons

  • Laterally and medially: Adjacent metacarpal bases via intermetacarpal joints

Attachments

  • Capsular attachment: Surrounding the carpometacarpal joint, reinforced by dorsal and palmar ligaments.

  • Ligamentous attachments:

    • Dorsal carpometacarpal ligaments: Stabilize posteriorly.

    • Palmar carpometacarpal ligaments: Reinforce the volar surface.

    • Interosseous ligaments: Connect adjacent metacarpal bases.

  • Tendinous and muscular attachments:

    • Base of 1st metacarpal: Attachment for abductor pollicis longus and part of opponens pollicis.

    • Base of 2nd metacarpal: Insertion of extensor carpi radialis longus.

    • Base of 3rd metacarpal: Insertion of extensor carpi radialis brevis.

    • Base of 5th metacarpal: Insertion of extensor carpi ulnaris.

Function

  • Forms the carpometacarpal joints, providing stability between hand and wrist.

  • Facilitates load transfer from the carpus to the metacarpal shafts during gripping and lifting.

  • Contributes to hand arching, improving precision grip and dexterity.

  • Provides tendinous anchor points for major wrist extensors and stabilizers.

  • The first metacarpal base allows thumb opposition and abduction, crucial for prehension.

Clinical Significance

  • Fractures: Common at the base of the first metacarpal (Bennett’s and Rolando fractures); may involve articular surface.

  • Dislocations: CMC dislocations can result from high-impact trauma or crush injuries.

  • Osteoarthritis: Degenerative changes common at the thumb CMC joint due to repetitive motion.

  • Ligament injuries: Disruption of dorsal or palmar CMC ligaments leads to instability.

  • Carpal boss: Bony prominence at base of 2nd or 3rd metacarpal due to chronic stress or degenerative change.

  • Imaging importance: Essential for assessing fractures, joint alignment, and degenerative conditions of the CMC region.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark, sharply defined)

    • Marrow: Bright due to fatty composition in adults

    • Articular cartilage: Smooth, thin intermediate-to-low signal layer covering the base

    • Ligaments: Low-signal linear structures around the joint capsule

    • Pathology: Fractures appear as linear low-signal defects; bone contusions as intermediate or slightly low signal areas

  • T2-weighted images:

    • Cortex: Low signal intensity

    • Marrow: Bright, slightly less than T1

    • Cartilage: Intermediate-to-bright, highlights surface irregularities

    • Joint fluid: Hyperintense; increased signal indicates effusion or inflammation

    • Pathology: Bone marrow edema and subchondral cysts appear as focal bright areas; osteoarthritis shows cartilage thinning and marginal osteophytes

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Pathologic areas: Bright hyperintense in edema, fracture, or osteitis

    • Sensitive for early bone stress or inflammatory changes

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark homogeneous signal

    • Abnormal: Bright hyperintensity with trabecular distortion in edema, bone bruise, or arthropathy

    • Excellent for assessing subtle cartilage damage, ligament injuries, and joint fluid

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Mild homogeneous enhancement

    • Inflamed or arthritic joints: Synovial and pericapsular enhancement

    • Fractures or infection: Patchy enhancement within marrow and soft tissues

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply outlined

  • Trabecular bone: Fine reticular pattern

  • Articular surface: Smooth and continuous; subchondral plate well visualized

  • Pathology: Reveals fractures, sclerosis, erosions, osteophytes, and joint incongruity

  • Carpal boss or degenerative changes: Easily identified by localized bony prominence or hypertrophy

CT VRT 3D image

Base of metacarpal bone CT 3D VRT image -img-00000-00000

MRI image

Base of metacarpal bone coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Base of metacarpal bone ct image

CT image

Base of metacarpal bone ct sag image