Surfaces and regions of the hand
The hand has two main surfaces: the palm (palma manus) and the dorsum (dorsum manus).
The entire skeleton of the hand is sequentially divided into three parts:
- Carpus (carpus)
- Metacarpus (metacarpus)
- Digits (digiti manus)
In anatomy, it is standard to use strict nomenclature for each digit:
- Thumb — Pollex, or digitus primus (I)
- Index finger — Index, or digitus secundus (II)
- Middle finger — Digitus medius, or digitus tertius (III)
- Ring finger — Digitus anularis, or digitus quartus (IV)
- Little finger — Digitus minimus, or digitus quintus (V)
Carpal bones (Ossa carpi)
The carpus is formed by eight spongy bones grouped into two rows. Bone counting in each row traditionally proceeds from the thumb (lateral) to the little finger (medial).
Proximal row:
- Scaphoid bone (os scaphoideum)
- Lunate bone (os lunatum)
- Triquetral bone (os triquetrum)
- Pisiform bone (os pisiforme) — a sesamoid bone embedded within a tendon.
Distal row:
- Trapezium bone (os trapezium)
- Trapezoid bone (os trapezoideum)
- Capitate bone (os capitatum) — the largest carpal bone.
- Hamate bone (os hamatum) — distinguished by a characteristic hook (hamulus ossis hamati).
On the palmar aspect of these bones, the carpal sulcus (sulcus carpi) is formed. Medially, it is bounded by the pisiform bone and the hook of the hamate. Laterally, the boundaries are formed by the tubercle of the scaphoid (tuberculum ossis scaphoideum) and the tubercle of the trapezium (tuberculum ossis trapezii).
Metacarpus and phalanges
Metacarpal bones (ossa metacarpi I–V) are five short tubular bones. Each consists of a massive base (basis ossis metacarpi) at the proximal end, a triangular body (corpus ossis metacarpi), and a distal head (caput ossis metacarpi) that articulates with the phalanges. Notably, the first metacarpal bone is the shortest and most massive of all.
Phalanges (phalanges digitorum manus) form the skeleton of the digits. From the 2nd to the 5th digit, each has three phalanges:
- proximal (phalanx proximalis)
- middle (phalanx media)
- distal (phalanx distalis)
The exception is the thumb (pollex), which lacks a middle phalanx and consists only of proximal and distal phalanges. Like the metacarpals, each phalanx has a base, body, and head. A distinct feature of the distal phalanges is that they terminate in a tuberosity (tuberositas phalangis distalis).
Ossification process
The appearance of ossification centers in the carpus follows a specific pattern: the process starts in the distal row and progressively extends to the proximal row.
The approximate sequence of ossification is as follows:
- Os capitatum and Os hamatum (the largest bones of the distal row) — from the 2nd month of prenatal development or during the 1st–2nd year of life.
- Os triquetrum — at 3–4 years.
- Os lunatum — at 4–5 years.
- Os scaphoideum — at 5–6 years.
- Os trapezium — at 6–7 years.
- Os trapezoideum — at 7–8 years.
- Os pisiforme — last of all, at 8–14 years.
Briefly: answers to topical questions
Which hand muscles originate from the hook of the hamate bone?
Two muscles of the hypothenar eminence originate from the hook of the hamate bone.
- Flexor digiti minimi brevis (m. flexor digiti minimi brevis) — originates from the hook of the hamate and the flexor retinaculum, flexing the proximal phalanx of the 5th digit.
- Opponens digiti minimi (m. opponens digiti minimi) — originates from the hamulus ossis hamati and inserts onto the ulnar border of the 5th metacarpal bone, opposing the little finger.
Which vessels and nerves pass through the carpal canal (canalis carpalis)?
Through the carpal canal (canalis carpi), the only nerve that passes is the median nerve; blood vessels are not described as part of its contents.
- Median nerve (n. medianus) — located superficially within the connective tissue between the tendons, directly beneath the flexor retinaculum (retinaculum musculorum flexorum).
In addition to the nerve, the tendons of the superficial and deep flexors of the digits, as well as the tendon of the flexor pollicis longus, pass through the canal.
During the exam, it is important to be able to sketch the carpal diagram by hand, clearly separating the 8 bones into proximal and distal rows, starting the count from the thumb.
Class and exam questions
How many phalanges does the thumb have?
The thumb (pollex) has only two phalanges: proximal and distal. It lacks a middle phalanx.
What are the boundaries of the carpal sulcus (sulcus carpi)?
Medially, the sulcus is bounded by the pisiform bone and the hook of the hamate. Laterally, by the tubercles of the scaphoid and trapezium bones.
Which carpal bone ossifies last?
Pisiform bone (os pisiforme). The ossification center appears in it last, at approximately 8–14 years of age.
To which bone type does the pisiform bone belong?
The pisiform bone is a sesamoid bone, as it develops within the thickness of a muscle tendon.
What else to study on this topic
- Formation and boundaries of the carpal sulcus (sulcus carpi)
- Anatomical features of the 1st metacarpal bone compared to the others
- Structure of the tuberosity of the distal phalanges of the fingers
- Localization of the pisiform bone and its relationship with tendons
- Chronology of the appearance of ossification centers in the bones of the hand
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