Anterior wrist region and carpal canal
The central structure of the anterior surface is the carpal canal (canalis carpi). It is an osseofibrous space through which flexor tendons and nerves pass from the forearm to the hand.
Walls of the canal:
- Anterior wall: formed by the denser, superficial part of the flexor retinaculum (retinaculum musculorum flexorum).
- Posterior wall: formed by the carpal bones and the adjacent deep layer of the retinaculum.
Topography of contents: Inside the canal, the elements are arranged in a strictly defined manner. The medial part of the space is occupied by the tendons of the deep and superficial flexors of the 2nd, 3rd, 4th, and 5th digits. Lateral to this bundle runs the tendon of the flexor pollicis longus (m. flexor pollicis longus). The most critical element—the median nerve (n. medianus)—lies most superficially in loose connective tissue, positioned between the tendon groups.
Posterior wrist region
On the posterior (dorsal) side of the wrist (regio carpalis posterior), the extensor tendons are enclosed in specialized synovial sheaths. These structures ensure unobstructed tendon gliding.
Special attention is paid to the tendon sheath of the radial wrist extensors (vagina tendinum mm. extensorum carpi radialium). It originates approximately 20–30 millimeters proximal to the extensor retinaculum (retinaculum extensorum). Descending below this ligament, the common sheath divides into isolated compartments that accompany the tendons down to their bony attachment points. Clinically, it is important to remember that the synovial sheaths of this muscle group can communicate with the radiocarpal joint cavity, facilitating the spread of inflammatory processes.
The sixth canal, passing along the lateral surface of the radial styloid process, is distinguished separately. It contains the tendons of the abductor pollicis longus and extensor pollicis brevis muscles. Their synovial sheath also begins 2–3 cm above the extensor retinaculum and extends distally to the level of the scaphoid bone.
Blood supply: dorsal carpal network
The structures of the dorsal hand and wrist are supplied by the dorsal carpal network (rete carpale dorsale). It is located deeply, directly beneath the extensor tendons.
This vascular network is formed by:
- Dorsal carpal branches arising from the ulnar and radial arteries.
- Small branches from the interosseous arteries of the forearm.
Branches supplying nearby joints originate from the network. Additionally, it gives rise to the dorsal metacarpal arteries (aa. metacarpeae dorsales), which course into the 2nd, 3rd, and 4th interosseous spaces.
Radial side and anatomical snuffbox
On the radial side of the wrist lies a characteristic topographic landmark—the anatomical snuffbox. This is a triangular depression that is clearly visible under the skin upon maximum abduction of the thumb.
Boundaries of the snuffbox:
- On the radial side: bounded by the tendons of the abductor pollicis longus (m. abductor pollicis longus) and extensor pollicis brevis (m. extensor pollicis brevis).
- On the ulnar side: bounded by the robust tendon of the extensor pollicis longus (m. extensor pollicis longus).
Layer-by-layer structure of the depression:
- In the subcutaneous fat layer run the cephalic vein (v. cephalica) and the superficial branch of the radial nerve (ramus superficialis n. radialis).
- Deeper, beneath the deep fascia, lies the radial artery (a. radialis).
The clinical significance of this zone is that the radial artery lies directly adjacent to the scaphoid bone (os scaphoideum) here. This allows the physician not only to palpate the vascular pulse but also to firmly compress the vessel against the bone to temporarily stop arterial bleeding.
Briefly: answers to topical questions
What passes through the ulnar canal of the wrist (Guyon's canal)?
The ulnar neurovascular bundle passes through the ulnar canal of the wrist (Guyon's canal), which is formed by a splitting of the deep fascia.
- Ulnar artery (a. ulnaris) and ulnar veins — located superficially and laterally in the canal.
- Palmar branch of the ulnar nerve (as part of the ulnar nerve, n. ulnaris) — lies deeper and medially.
Which tendons pass through the six osseofibrous canals beneath the extensor retinaculum?
Beneath the extensor retinaculum (retinaculum mm. extensorum), the tendons of the wrist and finger extensors pass within osseofibrous canals, surrounded by synovial sheaths.
- Canal of the extensor carpi ulnaris — tendon of m. extensor carpi ulnaris.
- Canal of the radial extensors — tendons of the extensor carpi radialis longus and brevis (mm. extensores carpi radiales longus et brevis).
- Canal of the extensor digitorum and extensor indicis — tendons of m. extensor digitorum and m. extensor indicis.
- 6th canal — tendons of m. abductor pollicis longus and m. extensor pollicis brevis.
- The tendon of the extensor pollicis longus (tendo m. extensoris pollicis longi) also passes beneath the retinaculum.
The complete list of contents for all six canals is not provided in the cited sources.
Which nerves innervate the skin of the anterior and posterior surfaces of the wrist?
The sources describe the innervation of only the lateral and medial parts of the wrist; data on the anterior and posterior surfaces are absent. The skin of the wrist is innervated by:
- Medial cutaneous nerve of the forearm (n. cutaneus antebrachii medialis) — innervates the medial part of the wrist.
- Lateral cutaneous nerve of the forearm (n. cutaneus antebrachii lateralis) — innervates the lateral part of the wrist (thenar region).
To which carpal bones does the flexor retinaculum (retinaculum flexorum) attach?
The flexor retinaculum (retinaculum musculorum flexorum) attaches to four carpal bones, forming the walls of the carpal tunnel.
- On the radial side (laterally): attaches to the scaphoid bone (os scaphoideum) and trapezium (os trapezium).
- On the ulnar side (medially): attaches to the pisiform bone (os pisiforme) and hamate (os hamatum).
Class and exam questions
What structures form the walls of the carpal tunnel?
The anterior wall of the canal is formed by the superficial part of the flexor retinaculum, and the posterior wall by the carpal bones and the deep layer of the same retinaculum.
Where exactly is the median nerve located in the wrist region?
The median nerve passes inside the carpal tunnel. It lies most superficially in the connective tissue, positioned between the flexor tendons.
What forms the boundaries of the anatomical snuffbox?
On the radial side, the depression is bounded by the tendons of the abductor pollicis longus and extensor pollicis brevis, and on the ulnar side by the tendon of the extensor pollicis longus.
What is the clinical significance of the anatomical snuffbox?
In this triangular space beneath the fascia runs the radial artery, which lies closely apposed to the scaphoid bone. This is a convenient site to check the pulse or compress the artery during trauma.
What else to study on this topic
- Topography of the fascial spaces of the hand
- Projection of the flexor synovial sheaths onto the palm
- Relationship between synovial sheaths and the development of hand phlegmon
- Carpal tunnel syndrome (median nerve compression neuropathy)
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