Overview
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.
Gross Anatomy
The Carpal Tunnel
|
Roof |
Flexor
Retinaculum (otherwise known as transverse carpal ligament |
|
Floor |
Articulated
Carpal Bones |
|
Content* |
Flexor
Digitorum Superficialis (FDS - 2nd to 5th digit) |
|
|
Flexor
Digitorum Profundus (FDP - 2nd to 5th digit) |
|
|
Flexor
Pollicis Longus (FPL) |
|
|
Median
Nerve |
Note: Flexor Carpi Radialis (FCR) lies in
a separate fibrous compartment
Flexor Retinaculum
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.
Median
Nerve
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.
Flexor
Tendons
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.
Guyon’s Canal
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.
Clinical Anatomy
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
Quick Anatomy
Key Facts
Aide-Memoire
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)
Summary
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.
References
References:
- Whitaker RH, Borley NR. Instant Anatomy. John Wiley & Sons; 2010
- Harold Ellis and Vishy Mahadevan, Clinical
Anatomy. John Wiley & Sons); 2013
- http://www.orthobullets.com/hand/6018/carpal-tunnel-syndrome