The carpal tunnel is a space found on the volar aspect of the wrist, bounded by the carpal bones and the flexor retinaculum. Within the tunnel lies all flexor tendons of the fingers and the median nerve. volume changes within the carpal tunnel secondary to degenerative changes, swelling or inflammation can lead to a compressive neuropathy of the median nerve called carpal tunnel syndrome.
The Carpal Tunnel
Flexor Retinaculum (otherwise known as transverse carpal ligament
Articulated Carpal Bones
Flexor Digitorum Superficialis (FDS - 2nd to 5th digit)
Flexor Digitorum Profundus (FDP - 2nd to 5th digit)
Flexor Pollicis Longus (FPL)
Note: Flexor Carpi Radialis (FCR) lies in a separate fibrous compartment
The flexor retinaculum is a quadrangular-shaped dense fibrous band that arches over the carpal bones. On the radial aspect, it is attached to the tubercle of the scaphoid proximally, and attached distally to the volar aspect of the trapezium. On the ulnar side, the retinaculum is attached to the pisiform proximally and the hook of hamate on the distal end.
Flexor retinaculum receives contribution from the palmaris longus tendon proximally, and is continuous to the palmar aponeurosis distally. Several structures overlie the retinaculum: ulnar nerve and artery (within Guyon’s canal) and palmar branches of the medial nerves.(don’t confuse with dorsal sensory branch of ulnar nerve)
Contents of the Carpal Tunnel
The tunnel contains one nerve and nine flexor tendons.
The median nerve (C5-T1) is a major peripheral nerve of the upper limb, which provides both motor and sensory innervations.
- Motor innervations: LLOAF
- First and second Lumbricals (from the palmar digital branches)
- The following thenar muscles – Oppenens pollicis, Abductor pollicis brevis (median nerve doesn’t supply all thenar muscle)
- Flexor muscles of the forearm, includes FPL (with exception of flexor carpi ulnaris and the ulnar part of FDP)
- Sensory innervations:
- Lateral part of the palm I would say “thenar skin” (from the palmar cutaneous branch,)
- Lateral three and half digits, palmar surface, and the corresponding nailbeds (from the palmar digital branches)
The median nerve gives off the palmar cutaneous in the forearm before it enters the carpal tunnel in the midline, between the ulnar side of the FCR and the palmaris longus. Once it passes through the carpal tunnel, the median nerve divides into branches, namely the recurrent “motor” branch and the palmar digital branches. The functions of the branches of the median nerve are described above.
The superficial (FDS) and deep (FDP) flexor tendons of the fingers are all surrounded within the same synovial sheath. Within the sheath, the FDPs lie deeper to FDS. The long flexor tendon of the thumb (FPL) is contained in a separate sheath below the FDS and FDP tendons
Within the transverse carpal ligament exists a separate compartment where the tendon of FCR passes through. It is important to understand that this is a separate compartment and the FCR tendon should not be considered as a part of the contents of the carpal tunnel.
This is a fibrous sheath that lies superficial to the ulnar aspect of the flexor retinaculum. The canal contains ulnar nerve and ulnar artery. It is important to recognise that Guyon’s Canal is considered separate to the carpal tunnel, as the contents of both of these structures are frequently a source of confusion.
Carpal Tunnel Syndrome
Carpal Tunnel Syndrome is the most common entrapment neuropathy of the body. Caused by compression of the median nerve within the carpal tunnel, clinic features include paraesthesia along the distribution of the median nerve, motor weakness and wasting of the thenar musculature. The symptoms may be worse during the night and wake the patient up partly because most people sleep with their wrists partially flexed. Atrophy of the thenar muscles can be seen in long-standing cases of carpal tunnel syndrome. Sparing of palmar “thenar” sensation is usually observed as the palmar cutaneous branch of the median nerve arises proximal to the flexor retinaculum, therefore spared from compression within the carpal tunnel.
There are several “provocation” tests that are described to help diagnose carpal tunnel syndrome, all of which attempt to reproduce the paraesthesia in the distribution of the median nerve
- Durkan’s Test:
- Direct compression over the carpal tunnel for 30 seconds.
- Tinel's test
- Tapping the median nerve over the carpal tunnel
- Phalen’s Test
- Wrist volar flexion (reverse prayer) for 30 - 60 sec.
First line treatment consists of simple analgesia, night splinting with wrist extension, and avoidance of aggravating activity. Corticosteroid injections to the carpal tunnel to alleviate inflammation and swelling also can be considered. surgical carpal tunnel decompression is considered if symptoms persist
Median Nerve Motor Supply: LLOAF (1st/2nd Lumbricals, OP, APB, Forearm flexors (inc. FPL) except FCU and ulnar part FDP)
Structures superficial to the carpal tunnel: UP UP (Ulnar Artery, Palmaris longus, Ulnar Nerve, Palmar branch of median nerve)
The carpal tunnel is found on the volar aspect of the wrist, bounded by the carpal bones and the flexor retinaculum, it contains nine flexor tendons and the median nerve. Carpal tunnel syndrome is the most common entrapment neuropathy, leading to pain and paraesthesia along the median nerve distribution. In severe cases, surgical release is required to alleviate the increased pressure within the tunnel. Another indication for carpal tunnel release is for distal radius fractures with severe swelling, and is usually performed in a prophylactic manner.
- Whitaker RH, Borley NR. Instant Anatomy. John Wiley & Sons; 2010
- Harold Ellis and Vishy Mahadevan, Clinical Anatomy. John Wiley & Sons); 2013