Upper limb · Hand
Metacarpal bones
The five metacarpals form the skeleton of the palm, between the carpus and the proximal phalanges. They are numbered from the thumb (first) to the little finger (fifth); their heads are the knuckles.
- Latin (TA)
- Ossa metacarpi
- Type
- Miniature long bones: each has a base, a shaft
- Side
- Paired — right and left
- Model size
- 8.7 cm longest
Showing a right set. Rotate it to inspect every surface; switch sides to practise siding.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
4 of 9 marked on the modelTap a landmark to find it on the bones and read what it is.
The expanded proximal end of a metacarpal, with facets for the carpus and for neighbouring metacarpals.
Where: Proximal end of each metacarpal.
Why it matters: Forms the carpometacarpal joint; the pattern of facets on the base identifies which metacarpal it is.
Related: Carpometacarpal joints
Marked on the model at the point Z-Anatomy places this label.
The shaft between base and head, concave on its palmar side along its length.
Where: Middle part of each metacarpal.
Why it matters: Gives origin to the interossei; the dorsal surface has a flat triangular area near the head.
Marked on the model at the point Z-Anatomy places this label.
The rounded distal end of a metacarpal.
Where: Distal end of each metacarpal; the heads form the knuckles of a clenched fist.
Why it matters: Articulates with the base of a proximal phalanx at the metacarpophalangeal joint.
Related: Metacarpophalangeal joint
Viva: What forms the knuckles?
Marked on the model at the point Z-Anatomy places this label.
The slightly narrowed part just behind the head.
Where: Between the shaft and the head.
Why it matters: Common fracture site, especially in the fifth metacarpal (boxer's fracture).
A saddle-shaped articular surface on the base of the first metacarpal.
Where: Proximal end of the first metacarpal.
Why it matters: Articulates with the trapezium in the saddle joint that allows the thumb's wide range of movement, including opposition.
Related: Carpometacarpal joint of thumb
Viva: What type of joint is the carpometacarpal joint of the thumb?
A deep, grooved base that grips the trapezoid.
Where: Proximal end of the second metacarpal.
Why it matters: Identifies the second (longest) metacarpal; it also articulates with the trapezium, the capitate and the third metacarpal.
A small projection from the base of the third metacarpal.
Where: Dorsal surface of the base, on its lateral (radial) side.
Why it matters: Identifies the third metacarpal; extensor carpi radialis brevis inserts close to it.
Related: Extensor carpi radialis brevis
Marked on the model at the point Z-Anatomy places this label.
A tubercle on the medial side of the base of the fifth metacarpal.
Where: Medial (ulnar) side of the base, which carries no articular facet.
Why it matters: Insertion of extensor carpi ulnaris; identifies the fifth metacarpal and its medial side.
Related: Extensor carpi ulnaris (insertion)
Classification & region
Miniature long bones: each has a base, a shaft (body) and a head.
- First metacarpal
- Thumb. The shortest and stoutest; its saddle-shaped base articulates with the trapezium; it lies in a different plane from the others, which allows opposition.
- Second metacarpal
- Index finger. The longest; its base is notched to receive the trapezoid and also touches the trapezium and capitate.
- Third metacarpal
- Middle finger. Recognised by the styloid process on the dorsolateral side of its base; articulates with the capitate.
- Fourth metacarpal
- Ring finger. Slender, with a small base that articulates with the capitate and hamate.
- Fifth metacarpal
- Little finger. Its base articulates with the hamate only and has a tubercle on its medial side.
Hold it in the anatomical position
- Hold a metacarpal with the rounded head distal and the irregular base, with its flat articular facets, proximal.
- The shaft is concave on its palmar surface along its length; the dorsal surface carries a flat triangular area near the head.
- In the articulated hand the first metacarpal sits in front of the others and is rotated, so its palmar surface faces medially towards the palm.
Right or left? Side determination
- First place the bone: head distal, concave palmar surface forwards, flat triangular dorsal area behind.
- Identify which metacarpal it is from its base: saddle facet (first), notched base for the trapezoid (second, the longest), styloid process (third), small base with facets on both sides (fourth), non-articular medial side with a tubercle (fifth).
- Second: the facet for the third metacarpal is on the medial side of the base.
- Third: the styloid process is on the dorsal surface of the base, on its lateral (radial) side.
- Fifth: the side of the base with no facet, carrying the tubercle for extensor carpi ulnaris, is medial.
- With the bone placed and its medial or lateral side fixed, decide which hand it fits. The first and fourth metacarpals are harder to side in isolation; say so if asked.
Check yourself: switch the 3D model to “Left bone” and apply the same steps.
Articulations
- With the distal row of carpal bones at the Carpometacarpal joints — Bases: first with trapezium; second with trapezoid (and trapezium, capitate); third with capitate; fourth with capitate and hamate; fifth with hamate..
- With the neighbouring metacarpals at the Intermetacarpal joints — Small facets on the sides of the bases of the second to fifth metacarpals..
- With the proximal phalanges at the Metacarpophalangeal joints — Heads..
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Abductor pollicis longus | insertion | Lateral side of the base of the first metacarpal. |
| Opponens pollicis | insertion | Lateral border of the shaft of the first metacarpal. |
| Flexor carpi radialis | insertion | Palmar surface of the base of the second metacarpal (and often the third). |
| Extensor carpi radialis longus | insertion | Dorsal surface of the base of the second metacarpal. |
| Extensor carpi radialis brevis | insertion | Dorsal surface of the base of the third metacarpal, near the styloid process. |
| Extensor carpi ulnaris | insertion | Tubercle on the medial side of the base of the fifth metacarpal. |
| Opponens digiti minimi | insertion | Medial border of the shaft of the fifth metacarpal. |
| Adductor pollicis (transverse head) | origin | Palmar surface of the shaft of the third metacarpal. |
| Adductor pollicis (oblique head) | origin | Bases of the second and third metacarpals (with the capitate). |
| Dorsal interossei | origin | Adjacent sides of the shafts of neighbouring metacarpals. |
| Palmar interossei | origin | Palmar surfaces of the shafts of the metacarpals of the fingers they act on (second, fourth and fifth), on the side facing the middle finger. Some texts count a fourth palmar interosseous, on the first metacarpal. |
| Collateral ligaments of the metacarpophalangeal joints; deep transverse metacarpal ligaments | ligament | Sides of the heads; the deep transverse metacarpal ligaments join the palmar plates of the second to fifth MCP joints. |
Functions
- Form the skeleton of the palm and support its arches.
- Carry the fingers and thumb, and transmit grip forces to the wrist.
- Give origin to the interossei and insertion to the wrist muscles.
- The mobile first metacarpal lets the thumb oppose the fingers.
Clinical & practical relevance
- Boxer's fracture: a fracture of the neck of the fifth (sometimes fourth) metacarpal from punching with a closed fist; the head tilts towards the palm.
- Bennett's fracture: a fracture-dislocation through the base of the first metacarpal, involving the carpometacarpal joint of the thumb.
- The second and third metacarpals are held almost immobile at their carpometacarpal joints, giving the hand a stable central pillar; the fourth and fifth are more mobile.
Identification tips
- Count from the thumb: first is the thumb, fifth is the little finger.
- Base = proximal with flat facets; head = distal and rounded. The head is the knuckle.
- Only the third has a styloid process; of the finger metacarpals, only the fifth has a base with a bare, non-articular medial side.
Common student mistakes
- Calling the base the head: the head is distal.
- Numbering from the little finger instead of the thumb.
- Saying the third metacarpal is the longest; the second is.
- Putting the styloid process on the palmar surface; it is dorsal.
Common exam questions
Which is the longest metacarpal and which is the shortest?Show answer
The second is the longest; the first is the shortest and stoutest.
How do you identify the third metacarpal?Show answer
By the styloid process on the dorsolateral side of its base.
Which metacarpal articulates with the hamate only?Show answer
The fifth (the fourth articulates with both capitate and hamate).
Which muscles insert into the bases of the metacarpals?Show answer
Abductor pollicis longus (first), flexor carpi radialis and extensor carpi radialis longus (second), extensor carpi radialis brevis (third), extensor carpi ulnaris (fifth).
What is a boxer's fracture?Show answer
A fracture of the neck of the fifth metacarpal.
What type of joint is the first carpometacarpal joint?Show answer
A saddle joint, between the trapezium and the base of the first metacarpal.
Revision summary
- Five miniature long bones: base, shaft, head.
- First: shortest, saddle base with trapezium.
- Second: longest, notched base for trapezoid.
- Third: styloid process; capitate.
- Fifth: hamate only; medial tubercle for extensor carpi ulnaris.
- Heads = knuckles; MCP joints with proximal phalanges.
- Boxer's (fifth neck) and Bennett's (first base) fractures.
Test yourself on the metacarpal bones
Spotting questions on bones, sides and landmarks — untimed, with explanations.
Joints of the metacarpal bones
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
- Kervyn G, Zielinski M, Vinent L, et al. Z-Anatomy: the libre 3D atlas of anatomy. Models derived from BodyParts3D, The Database Center for Life Science (CC BY-SA 2.1 JP). CC BY-SA 4.0. www.z-anatomy.com/
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy