science

First metacarpal bone

First metacarpal bone is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand First metacarpal bone rather than just read about it. In short: The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpophalangeal joint.

Key takeaways

First metacarpal bone belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect First metacarpal bone to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of First metacarpal bone from memory before moving on to harder problems.

Reference excerpt

The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpophalangeal joint.

Characteristics The first metacarpal bone is short and thick with a shaft thicker and broader than those of the other metacarpal bones. Its narrow shaft connects its widened base and rounded head; the former consisting of a thick cortical bone surrounding the open medullary canal; the latter two consisting of cancellous bone surrounded by a thin cortical shell.

Head The head is less rounded and less spherical than those of the other metacarpals, making it better suited for a hinge-like articulation. The distal articular surface is quadrilateral, wide, and flat; thicker and broader transversely and extends much further palmarly than dorsally. On the palmar aspect of the articular surface there is a pair of eminences or tubercles which articulate with the radial and ulnar sesamoid bones of the thumb metacarpophalangeal joint; the lateral eminence is larger than the medial.

Body/Shaft The body or shaft is thick and broad — averaging 6 to 11 millimetres (0.24 to 0.43 in). On its dorsal side, the shaft is flat and wide, while the anteroposterior side is less pronounced; usually resulting in an oval-triangular cross-section. The dorsal surface of the shaft is weakly convex longitudinally, while its palmar, radial, and ulnar surfaces tend to be concave. The palmar and medial surface exhibits a blunt ridge which separates a larger lateral part – the insertion of the opponens pollicis muscle – and a smaller medial part – the origin of the lateral head of the first dorsal interosseous muscle.

Base The base is significantly different from the bases of the other metacarpals. It is trumpet-shaped and ends in a saddle-shaped articular surface matching that of the trapezial articular surface. The configuration of the thumb carpometacarpal joint plays an important role in the mechanism of opposition. The articular surface is delimited by a thick, crest-like ridge extending around its circumference. On the palmar and lateral side of the base is the insertion of the tendon of the abductor pollicis longus muscle, usually featuring a small tubercle. The origin of the first dorsal interosseous muscle is on the ulnar aspect of the base, and can sometimes extend onto the shaft. In contrast to the other metacarpals, the first metacarpal has no articular facets on the sides of its base (for intermetacarpal articulations) because it articulates exclusively with the trapezium.

Ossification

The metacarpal bone of the thumb has two centres of ossification: a primary centre in the shaft and a secondary centre in the base. This contrasts to the other four metacarpal bones where the secondary centre is found in the head. The ossification process begins in the shaft during the ninth week of prenatal life, and in the base during the second year of life in girls and the third year in boys. When the both sexes were considered together, the ossification of base of first metacarpal was seen to start between 13 and 41 months. These centres unite before fifteenth year in girls and seventeenth year in boys.

The thumb has several associated accessory bones. When present, these bones are usually found near the base and trapezium and are the products of an additional centre of ossification, usually of the trapezium, that failed to fuse with the associated bone. Named accessory bones include:

os trapezium secundarium - between the ulnar base of the first metacarpal and the distal margin of the trapezium os praetrapezium - between the thumb metacarpal and the distal aspect of the trapezium os paratrapezium - between the radial base of the first metacarpal and the distoradial aspect of the trapezium

Fractures Fractures to metacarpal bones account for 30-40% of all hand fractures, of which 25% occur in the first metacarpal (second to fractures to the fifth metacarpal bone). 80% of fractures to the first metacarpal occur at its base.

Metacalamity classification

Metacalamity classification is a system for classifying fractures of the first metacarpal base. It helps physicians to describe fractures accurately and easily, as it encompasses well-known eponyms such as Bennett fracture or Rolando fracture. Metacalamity classification divides the first metacarpal base fracture into extra-articular (marked by "E") and intra-articular (marked by "I"), involving the first carpometacarpal joint, subsequent number increases with severity. Extra-articular (E)

E1 - Transverse fracture E2 - Oblique or spiral fracture E3 - Comminuted fracture Intra-articular (I)

I1 - Simple intra-articular fracture with main palmar-ulnar fragment (Bennett's fracture) I2 - "Y" or "T" shaped intra-articular fracture (Rolando's fracture) I3 - Comminuted intra-articular fracture

Additional images

Notes

References

Illustrations

Worked examples

Example 1 — a first encounter with First metacarpal bone

Start with the simplest possible case. Write down what First metacarpal bone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to First metacarpal bone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about First metacarpal bone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of First metacarpal bone

In research: First metacarpal bone appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses First metacarpal bone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: First metacarpal bone is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bones of the hand, Metacarpus, so understanding it makes those chapters shorter.
In everyday life: Look for First metacarpal bone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study First metacarpal bone in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what First metacarpal bone means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain First metacarpal bone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is First metacarpal bone in simple terms?

Why does First metacarpal bone matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study First metacarpal bone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on First metacarpal bone.