Learning Objectives

By the end of this article, learners should be able to:

Describe the anatomical boundaries of the carpal tunnel
List and identify the contents of the carpal tunnel
Understand the functional anatomy of the median nerve at the wrist
Recognise the clinical features, examination findings, and management of carpal tunnel syndrome

The carpal tunnel is a narrow fibro-osseous passageway located on the anterior aspect of the wrist. It serves as the main conduit through which the median nerve and several long flexor tendons pass from the forearm into the palm.

Because the space within the tunnel is limited, even small increases in its contents or reductions in its volume can result in median nerve compression, leading to carpal tunnel syndrome.

Borders of the Carpal Tunnel

Two main structural components form the carpal tunnel:

A deep carpal arch, which forms the floor and sides
A superficial flexor retinaculum, which forms the roof

Together, these structures convert the carpal arch into a rigid tunnel.

Carpal Arch

Concave on the palmar surface, forming the base and lateral walls of the tunnel
Laterally formed by the tubercles of the scaphoid and trapezium
Medially formed by the pisiform and the hook of the hamate

Flexor Retinaculum (Transverse Carpal Ligament)

A thick band of connective tissue forms the roof of the carpal tunnel
Bridges the medial and lateral aspects of the carpal arch, converting it into a tunnel
Extends:
- Medially from the pisiform and the hook of the hamate
- Laterally to the scaphoid and trapezium

Clinically, the distal wrist crease corresponds to the proximal entrance of the carpal tunnel.

Contents of the Carpal Tunnel

The carpal tunnel contains nine tendons and the median nerve, all tightly packed within a confined space.

Important: The palmar cutaneous branch of the median nerve arises proximal to the carpal tunnel and travels superficial to the flexor retinaculum—this explains why palmar sensation is preserved in carpal tunnel syndrome.

Tendinous Contents

The nine tendons passing through the carpal tunnel are:

Flexor pollicis longus (1 tendon)
Flexor digitorum profundus (4 tendons)
Flexor digitorum superficialis (4 tendons)

The eight digital flexor tendons (FDP and FDS) share a common synovial sheath, while the tendon of flexor pollicis longus is enclosed within its own synovial sheath. These sheaths reduce friction, allowing for smooth tendon movement.

Common misconception: The tendon of flexor carpi radialis does not pass through the carpal tunnel—it runs within the flexor retinaculum in a separate compartment.

Median Nerve

After passing through the carpal tunnel, the median nerve divides into:

Recurrent (thenar) branch – supplies the thenar muscles
Palmar digital branches – provide:
- Sensory innervation to the palmar skin and dorsal nail beds of the lateral 3½ digits
- Motor innervation to the lateral two lumbricals

Clinical Relevance: Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) results from compression of the median nerve within the carpal tunnel. It is the most common mononeuropathy of the upper limb.

Aetiology

Often idiopathic
Can result from:
- Thickening of the flexor retinaculum
- Synovial sheath hypertrophy
- Inflammatory conditions or repetitive wrist use

Clinical Features

Numbness, tingling, and pain in the median nerve distribution
Symptoms may radiate proximally into the forearm
Nocturnal symptoms are common, often waking patients from sleep
Advanced disease may cause weakness and atrophy of the thenar muscles

Clinical Examination

Provocative tests include:

Tinel’s sign – percussion over the carpal tunnel reproduces paraesthesia
Phalen’s manoeuvre – sustained wrist flexion for 60 seconds reproduces symptoms

Management

First-line: nocturnal wrist splinting in slight dorsiflexion
Second-line: corticosteroid injection into the carpal tunnel
Definitive: surgical decompression by division of the flexor retinaculum in severe or refractory cases