Palm and
Digits Anatomy
The hand
comprises the wrist (carpus), the palm (metacarpus) and the digits (Figs 3.37
& 3.38). The palm of the hand (Fig. 3.39) contains the palmar aponeurosis,
intrinsic muscles, tendons originating from muscles in the anterior compartment
of the forearm, and palmar vessels and nerves. The intrinsic muscles comprise
the thenar and hypothenar groups, the lumbricals and interossei, and adductor
pollicis. The tendons enter the palm through the carpal tunnel (Fig. 3.98) deep
to the flexor retinaculum. The skin of the anterior surface of the hand is
thick, devoid of hair and contains many sweat glands. It is firmly bound to the
underlying deep fascia, producing characteristic creases. Skin over the palmar
surface of each distal phalanx is firmly tethered to the periosteum by fibrous
septa, which enclose fat-filled spaces. Infection causing increased pressure
in the pulp space may result in thrombosis of vessels supplying the distal
phalanx causing bone necrosis.
The deep fascia of the palm is
thickened centrally to form the triangular palmar aponeurosis (Fig. 3.39) and
is thinner at each side where it covers the thenar and hypothenar muscles.
Proximally, the palmar aponeurosis attaches to the flexor retinaculum and is
continuous with the tendon of palmaris longus. Distally, the aponeurosis gives
rise to four pairs of digital slips, which cross the metacar- pophalangeal
joints and attach to the proximal phalanges of the fingers via the fibrous
flexor sheaths. The aponeurosis covers the superficial palmar arch, the median
nerve and the tendons of the long flexors of the digits. Thickening and
shortening of the aponeurosis in Dupuytren’s contracture produces fixed flexion
of the metacarpophalangeal and proximal interphalangeal joints.
Lateral and medial septa pass
from the edges of the palmar aponeurosis to the first and fifth metacarpal
bones, respectively.
These septa separate the
thenar and hypothenar muscles from a central palmar space, which is traversed
by the palmar digital vessels and nerves and by the tendons of the long flexor
muscles of the fingers.
The subcutaneous tissue of the
medial side of the palm usually contains palmaris brevis (Fig. 3.39), a small muscle
attaching to the overlying skin and to the palmar aponeurosis.
The tendons of flexor pollicis
longus, flexor digitorum profundus and flexor digitorum superficialis enter the
hand deep to the flexor retinaculum (Fig. 3.99). On reaching the appropriate
digit, each tendon traverses a tunnel formed by the fibrous flexor sheath and
the phalanges (Fig. 3.40). The fibrous sheath is attached to the edges of the
anterior surfaces of the phalanges (Fig. 3.41) and continues as far as the distal
phalanx (Fig. 3.42).
The sheath is thinner and more flexible in front of the interphalangeal joints,
allowing flexion of the digit without ‘bowstringing’ of the tendons and thus
facilitating gripping. Within the flexor sheaths the tendons are invested by
synovial membrane and receive vincula tendinum, small folds of synovium that
convey blood vessels to the tendons.
Abductor pollicis brevis,
flexor pollicis brevis and opponens pollicis form the thenar eminence on the
lateral side of the palm. They attach proximally to the trapezium and scaphoid
and to the lateral part of the flexor retinaculum (Fig. 3.37).
Abductor pollicis brevis (Fig. 3.43) lies superficial
to the other thenar muscles and passes from the scaphoid to the base of the
proximal phalanx of the thumb. The muscle abducts the thumb, moving the digit
anteriorly at right angles to the plane of the palm.
Flexor pollicis brevis, lying
deep and medial to the abductor, passes from the trapezium to the proximal
phalanx of the thumb. The muscle flexes the carpometacarpal and
metacarpophalangeal joints, drawing the thumb across the palm (maintaining the
thumbnail at right angles to the palmar plane).
Opponens pollicis (Fig. 3.44), the deepest of
the thenar muscles, attaches proximally to the trapezium and distally to the
shaft of the first metacarpal. The muscle produces opposition of the thumb,
allowing pulp-to-pulp contact with the fingers. This movement combines flexion,
adduction and rotation of the first metacarpal at its carpometacarpal joint.
The thenar muscles are
supplied by the recurrent branch of the median nerve (Figs 3.43 & 3.44). Injury to this nerve may be
assessed by palpating the thenar muscles while the subject attempts abduction
of the thumb.
Abductor digiti minimi, flexor
digiti minimi brevis and opponens digiti minimi (Fig. 3.45) form the hypothenar eminence and attach
proximally to the pisiform, the hook of the hamate and the adjacent part of the
flexor retinaculum. Abductor digiti minimi passes from the pisiform to the base
of the proximal phalanx of the little finger and abducts the digit, moving it
medially in the plane of the palm. Flexor digiti minimi brevis attaches between
the hamate and base of the proximal phalanx of the little finger and flexes the
metacarpal and proximal phalanx of the little finger. Opponens digiti minimi
passes from the hamate to the shaft of the fifth metacarpal and on contraction
deepens the hollow of the palm.
The hypothenar muscles are
supplied by the deep branch of the ulnar nerve (Fig. 3.45).
Deep muscles
The deep muscles of the hand
consist of adductor pollicis, the palmar and dorsal interossei and the
lumbricals.
Adductor pollicis (Fig. 3.46) has transverse
and oblique heads. The transverse head attaches to the shaft of the third
metacarpal bone, and the oblique head to the trapezoid, capitate and bases of
the second and third metacarpals. Both heads pass laterally to attach to the
base of the proximal phalanx of the thumb by a common tendon which usually
contains a sesamoid bone (Fig. 3.38). The muscle adducts and flexes the thumb
at its carpometacarpal and metacarpophalangeal joints and is supplied by the
deep branch of the ulnar nerve (Fig. 3.54).
The interossei consist of
three palmar and four dorsal muscles (Fig. 3.47). Each palmar interosseous muscle (Fig. 3.48) arises by a
single head from the anterior border of the shaft of the second, fourth or
fifth metacarpal. Each dorsal interosseous muscle (Fig. 3.49) arises by two heads from the contiguous
sides of the shafts of the adjacent metacarpals. Distally the tendon of each
interosseous muscle attaches to the base of the proximal phalanx and to the
extensor expansion of the appropriate digit (Fig. 3.51). The interossei move
the fingers in the plane of the palm (coronal plane); movement of a finger away
from the long axis of the middle finger is called abduction while movement
towards the middle finger is adduction. The palmar interossei adduct and the
dorsal interossei abduct the fingers. In addition, the interossei flex the
metacarpophalangeal joints and extend the interphalangeal joints. All the
interossei are supplied by the deep branch of
the ulnar nerve
(Fig. 3.54). The
integrity of the
nerve and the adducting function
of the palmar interossei can be tested by gripping a sheet of paper between the
sides of two adjacent fingers.
The lumbricals are four small
muscles attaching proximally to the tendons of flexor digitorum profundus (Fig. 3.50). Distally, each
lumbrical attaches to the radial side of the extensor expansion of the
appropriate finger. The muscles extend the inter-phalangeal joints and flex the
metacarpophalangeal joints. The first and second lumbricals usually have only
one head each and are supplied by the median nerve, whereas the third and
fourth (medial) usually have two heads and are supplied by the ulnar nerve.
Each finger possesses an
extensor expansion or hood (Fig.
3.51), which receives the tendons of the
appropriate long extensor muscle(s), interossei and lumbricals. The broad
proximal part of the expansion overlies the metacarpophalangeal joint. Distally, the expansion tapers and attaches by a central slip to the base of the
middle phalanx and by two marginal slips to the base of the distal phalanx.
Blood vessels
The arterial supply to the
hand is derived from branches of the ulnar and radial arteries, which form
superficial and deep palmar arches linking the two main arteries and ensuring
a rich blood supply to the palm and fingers.
The ulnar artery enters the
hand super-ficial to the flexor retinaculum and gives a deep branch that
accompanies the deep branch of the ulnar nerve. The main artery continues as
the superficial palmar arch (Fig.
3.52), which passes distally to the level of the thumb web, lying
deep to the palmar aponeurosis but anterior to the digital nerves and flexor
tendons. The superficial palmar arch gives four palmar digital branches, which
supply the adjacent sides of the fingers (Fig. 3.53) and medial side of the
little finger, and is completed laterally by a branch of the radial artery.
The radial artery enters the
palm from the dorsum of the hand between the two heads of the first dorsal
interosseous muscle (Fig. 3.49). The artery gives branches to the thumb and
index finger and continues as the deep palmar arch (Fig. 3.54), which lies over
the bases of the metacarpal bones, deep to the flexor tendons, and is about 1
cm proximal to the superficial arch. The deep arch provides perforating
branches, which anastomose with dorsal metacarpal arteries, and three palmar
metacarpal arteries, which anastomose with the palmar digital arteries of the
superficial arch. The deep arch is completed medially by the deep branch of the
ulnar artery. Other vessels such as dorsal metacarpal arteries from the dorsal
carpal arch may provide an important supply of blood to the hand. The
anastomoses between branches of arteries supplying the hand usually provide an
adequate blood supply even if one artery is blocked.
Most venous blood from the
fingers and palm drains into superficial veins on the dorsum of the hand to
enter the cephalic or basilic veins.
Innervation of the anterior aspect
of the hand is shared by the ulnar and median nerves. The ulnar nerve supplies
more intrinsic muscles than the median nerve, which supplies a larger area of
skin.
The ulnar nerve
(Fig. 3.52) enters
the palm superficial to the flexor retinaculum and terminates as
superficial and deep branches. The superficial branch supplies digital branches
to the skin of the medial one and one-half digits. A corresponding area of the
palm is supplied by palmar branches that arise from the ulnar nerve in the
forearm. The deep branch of the ulnar nerve (Fig. 3.54) accompanies the deep palmar arch and
supplies the three hypothenar muscles, the medial two lumbricals, all the
interossei and adductor pollicis. The ulnar nerve also supplies palmaris
brevis. Injury to the ulnar nerve produces marked wasting (atrophy) of the
muscles between the first and second metacarpal bones. The median nerve
traverses the carpal tunnel and terminates as digital and recurrent branches.
The digital branches (Fig. 3.52) supply skin of the lateral three-and-one-half
digits and usually the lateral two lumbricals. A corresponding area of the palm
is supplied by palmar branches arising from the median nerve in the forearm.
The recurrent branch of the median nerve (Fig. 3.43) supplies the three thenar
muscles.
In the palm, the digital
branches of the ulnar and median nerves lie deep to the superficial palmar arch
(Fig. 3.52), but in the fingers they lie anterior to the digital arteries
arising from the superficial arch (Fig.
3.53). Although there may be variability of innervation of the ring
and middle fingers, the skin on the anterior surface of the thumb is always
supplied by the median nerve and that of the little finger by the ulnar nerve.
The palmar digital branches of the median and ulnar nerves also supply the nail
beds of their respective digits.
