Flexor
and Extensor Retinacula
The flexor and extensor retinacula are strong bands of deep fascia
that hold the long flexor and extensor tendons in position at the wrist.
Flexor Retinaculum
The flexor retinaculum is a thickening of deep fascia that holds
the long flexor tendons in position at the wrist. It stretches across the front
of the wrist and converts the concave anterior surface of the hand into an
osteofascial tunnel, the carpal tunnel, for the passage of the median nerve and
the flexor tendons of the thumb and fingers.
It is attached medially to the pisiform bone and the hook of
the hamate and laterally to the tubercle of the scaphoid and the trapezium
bones. The attachment to the trapezium consists of superficial and deep parts
and forms a synoviallined tunnel for passage of the tendon of the flexor carpi radialis.
The upper border of the retinaculum corresponds to the
distal transverse skin crease in front of the wrist and is continuous with the
deep fascia of the forearm. The lower border is attached to the palmar
aponeurosis
Extensor Retinaculum
The extensor retinaculum is a thickening of deep fascia that
stretches across the back of the wrist and holds the long extensor tendons in
position. It converts the grooves on the posterior surface of the distal ends
of the radius and ulna into six separate tunnels for the passage of the long
extensor tendons. Each tunnel is lined with a synovial sheath, which extends
above and below the retinaculum on the tendons. The tunnels are separated from
one another by fibrous septa that pass from the deep surface of the retinaculum
to the bones.
The retinaculum is attached medially to the pisiform bone
and the hook of the hamate and laterally to the distal end of the radius.
The upper and lower borders of the retinaculum are continuous with the deep fascia of the forearm and hand, respectively.
The upper and lower borders of the retinaculum are continuous with the deep fascia of the forearm and hand, respectively.
Carpal
Tunnel
The bones of the hand and the flexor retinaculum form the
carpal tunnel. The median nerve lies in a restricted space between the tendons
of the flexor digitorum superficialis and the flexor carpi radialis muscles.
Absent
Palmaris Longus
The palmaris longus muscle may be absent on one or both sides
of the forearm in about 10% of persons. Others show variation in form, such as
centrally or distally placed muscle belly in the place of a proximal one.
Because the muscle is relatively weak, its absence produces no disability.
Contents
of the Anterior Fascial Compartment of the Forearm
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Muscles: A superficial group, consisting of the pronator teres, the flexor
carpi radialis, the palmaris longus, and the flexor carpi ulnaris; an
intermediate group consisting of the flexor digitorum superficialis; and a deep
group consisting of the flexor pollicis longus, the flexor digitorum profundus,
and the pronator quadratus
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Blood supply to the muscles: Ulnar and radial arteries
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Nerve supply to the muscles: All the muscles are supplied by the median nerve
and its branches, except the flexor carpi ulnaris and the medial part of the
flexor digitorum profundus, which are supplied by the ulnar nerve.
