This thick, triangular deep fascia lies in the central part of the palm, with its apex at the flexor retinacu- lum and its base at the level of the heads of the met- acarpals. It stabilizes the palmar skin which is firmly addition, muscles are grouped together, based on
the attachments and actions: (1) muscles that arise from the humerus and pass to the hand (these act on the elbow, the wrist, and, in some instances, the joints of the digits); (2) muscles which arise from Fig. 8.1 Muscles on the back of the forearm. The subcutaneous posterior border of the ulna (dotted line) separates the flexor muscles medially from the extensor muscles laterally.
Copyright Dean Drobot/Shutterstock.
Extensor compartment of arm
Flexor compartment of arm
DISSECTION 8.1 Front of the forearm Objectives
I. To study the superficial muscles of the front of the fore- arm. II. To identify and trace the brachial, radial, and ulnar arteries, and the median and ulnar nerves. III. To study the palmaris brevis and palmar aponeurosis.
Instructions
1. Divide the deep fascia of the forearm vertically from the cubital fossa to the proximal margin of the flexor retinaculum. Make a transverse incision just proxi- mal to the retinaculum. Reflect the flaps of the fascia, but avoid cutting the structures deep to it.
2. The muscles uncovered consist of the flexor group medially and the extensor group laterally. Separate the most superficial muscle—the brachioradialis [Fig. 8.2]—on the lateral side of the front of the fore- arm. Follow it to its insertion on the lateral surface of the distal end of the radius.
3. Push aside the tendons of the abductor pollicis longus and extensor pollicis brevis which overlie the insertion of the brachioradialis, as they pass to the base of the thumb [see Fig. 8.21]. Avoid injury to the superficial branch of the radial nerve which crosses their superficial surface.
4. Pull the brachioradialis laterally. This exposes the ex- tensor carpi radialis longus and separates the exten- sor and flexor groups of muscles.
5. In the groove between the flexors and exten- sors, identify the radial artery and the superficial branch of the radial nerve. Follow them distally and proximally [Fig. 8.3]. In this way, find the origin of the artery from the brachial artery in the cubital fossa (occasionally high in the arm) and the branch from the deep branch of the radial nerve which supplies the extensor carpi radialis brevis—a muscle deep to the extensor carpi radialis longus.
6. Deep to the extensor carpi radialis brevis is the supi- nator muscle.
7. Separate the superficial group of flexor muscles.
These arise from the distal part of the medial su- pracondylar line and the medial epicondyle of the humerus. Most also have a minor attachment to the coronoid process of the ulna [see Figs. 6.2, 8.4].
These superficial muscles spread out from the me- dial epicondyle as a narrow fan with a vertical medial edge—the flexor carpi ulnaris [Fig. 8.2].
8. The most lateral muscle—the pronator teres— arises furthest superiorly and passes obliquely across the
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proximal half of the forearm to the point of maxi- mum convexity of the radius [Fig. 8.4]. It passes deep to the radial artery, the superficial branch of the ra- dial nerve, and the extensor muscles overlying the anterolateral surface of the radius [Fig. 8.2].
9. Medial to the pronator teres is the flexor carpi ra- dialis (the radial flexor of the wrist), which also takes an oblique course across the forearm. Its tendon disappears deep to the lateral part of the flexor reti- naculum, medial to the radial artery. Identify this tendon in your own wrist, and feel the pulsation of the radial artery (radial pulse) lateral to it on the distal margin of the radius.
10. Medial to the flexor carpi radialis is the palmaris lon- gus (if present). Follow its tendon superficial to the flexor retinaculum to join the palmar aponeurosis.
11. Beneath the tendon of the palmaris longus and be- tween it and the flexor carpi radialis, the median nerve becomes superficial, just proximal to the flexor retinaculum [Fig. 8.2].
12. The flexor carpi ulnaris is immediately medial to the palmaris longus in the proximal third of the fore- arm. Further distally, the two muscles separate, and the flexor digitorum superficialis appears between them [Fig. 8.2]. Follow the tendon of the ulnaris to its insertion on the pisiform bone.
13. Find the ulnar artery and nerve which become superficial between the tendons of the flexor carpi ulnaris and those of the flexor digitorum superficia- lis, just proximal to the flexor retinaculum. Here the artery and nerve pierce the deep fascia and enter the hand, superficial to the retinaculum, immediate- ly lateral to the insertion of the flexor carpi ulnaris.
They then pass deep to the palmaris brevis and di- vide into their terminal branches [Figs. 8.2, 8.5].
14. The palmaris brevis is a thin cutaneous muscle which arises from the palmar aponeurosis and flexor retinaculum. It passes transversely across the proximal 2–3 cm of the hypothenar eminence and is inserted into the skin on the medial side [Fig. 8.5]. It is supplied by the ulnar nerve. When it contracts, it bunches up the skin over the eminence, thus deepening the concavity of the palm and producing a cushion of skin against which the handle of a tool can be held steadily.
15. Expose the superficial surface of the flexor carpi ulnaris. Note its origin from the medial epicondyle, the olecranon, and the proximal two-thirds of the posterior (subcutaneous) border of the ulna [Fig. 8.6].
16. Follow the ulnar nerve from the arm, posterior to the medial epicondyle, then between the humeral and ulnar attachments of the flexor carpi ulnaris on its deep surface [see Figs. 7.6, 8.7]. Pull the flexor car- pi ulnaris medially, and expose the ulnar nerve on its deep surface lying on the flexor digitorum profun- dus which covers the ulna. Trace the nerve and the ulnar artery into continuity with the parts exposed at the wrist. Note the branches of the nerve to the flexor carpi ulnaris and flexor digitorum profundus, the dorsal branch arising near the middle of the forearm, and the small palmar branch [see Fig. 5.9]
which arises in the distal half of the forearm. Trace the dorsal branch to the medial side of the forearm.
17. Cut through the middle of the flexor carpi radialis, palmaris longus, and pronator teres muscles, and re- flect their parts. Identify the branches of the median nerve entering them proximally [Fig. 8.3].
18. The flexor digitorum superficialis is now exposed.
Identify the radial head of this muscle attached to the anterior border of the radius, deep to the distal part of the pronator teres [Figs. 8.3, 8.4].
19. Follow the median nerve from the cubital fossa between the radial and humero-ulnar heads of the flexor digitorum superficialis. Lift the medial edge of the muscle, and find the nerve on its deep surface.
Note its branches to the muscle. A short distance proximal to the wrist, the nerve becomes superficial between the tendons of the flexor carpi radialis and the palmaris longus. It gives off the palmar branch of the median nerve which enters the palm, superficial to the flexor retinaculum. The median nerve enters the hand, deep to the flexor retinaculum [Fig. 8.5].
Identify this position in your own wrist, and note how easily the nerve could be injured by a relatively superficial cut at this point.
20. Turn the tendon of the palmaris longus distally. Note its attachment to the flexor retinaculum and its con- tinuity with the apex of the palmar aponeurosis.
21. Complete the exposure of the superficial surface of the palmar aponeurosis and the slips which pass from its distal margin to each of the fingers. Note that the edges of each slip turn posteriorly into the palm, leaving spaces between the slips through which the digital vessels and nerves (and lumbri- cal muscles) escape from beneath the palmar aponeurosis into the fingers [Fig. 8.5]. Each slip of the aponeurosis is attached: (a) to the phalanges by
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fusing with the fibrous flexor sheath (the fibrous tun- nel in which the tendons of the long flexors lie); and (b) with the deep transverse metacarpal ligament (described later) [Fig. 8.5]. Confirm this arrangement by pushing a blunt instrument proximally between any two fingers—it passes readily into the palm, deep to the aponeurosis, without having to pierce it.
22. Separate the palmaris longus tendon and the aponeurosis from the surface of the flexor retinacu- lum. Turn the aponeurosis distally. You will need to
separate the edges of the aponeurosis from the thin- ner deep fascia covering the thenar and hypothenar muscles and divide the septum which passes back- wards from each edge. The septa fuse with the fascia anterior to the interosseous muscles and the adduc- tor pollicis [Fig. 8.8]. Avoid injury to the vessels and nerves immediately deep to the aponeurosis.
23. Remove the fat from the interdigital region, and ex- pose the digital nerves and vessels, with a lumbri- cal muscle posterior to them [Fig. 8.5].
Biceps Deep fascia of arm
Medial intermuscular septum Brachialis
Brachial A.
Median N.
Pronator teres
Bicipital aponeurosis
Flexor carpi radialis
Flexor carpi ulnaris
Flexor digitorum superficialis
Median N.
Flexor pollicis longus
Flexor retinaculum Pisiform Ulnar A.
Ulnar N.
Palmaris longus Lateral cutaneous N.
of forearm Brachialis Brachioradialis Biceps
Radial A.
Extensor carpi radialis longus
Radial A.
Flexor digitorum superficialis
Flexor pollicis longus Radial N. (superficial branch) Pronator quadratus
Superficial palmar branch Radial A.
Fig. 8.2 Dissection of superficial muscles, arteries, and nerves of the front of the forearm. Part of the radial artery was removed to show the muscles deep to it.
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Front of the forearm and hand
Fig. 8.3 Deep dissection of muscles and nerves of the front of the forearm. The division of the brachial artery is slightly lower than usual.
Biceps
N. to flexor digitorum superficialis
Radial head of flexor digitorum superficialis Brachialis
N. to muscles of common flexor origin Brachial A.
Median N.
Pronator teres (ulnar head)
Flexor carpi radialis
Flexor carpi radialis
Flexor carpi ulnaris Flexor digitorum superficialis Flexor digitorum superficialis
Flexor digitorum superficialis
Ulnar N.
Palmaris brevis Ulnar N.
Ulnar A.
Palmaris longus
Palmaris longus N. to extensor carpi radialis longus
N. to extensor carpi radialis brevis
Extensor carpi radialis brevis Brachialis Brachioradialis
Radial N. (superficial branch) Radial N. (deep branch) Radial recurrent A.
Extensor carpi radialis longus Anterior interosseous N.
Supinator
Radial A.
Pronator teres
Flexor digitorum profundus Flexor pollicis longus
Radial N. (superficial branch) Brachioradialis
Abductor pollicis longus
Superficial palmar branch
Median N. and A.
adherent to it. Medially and laterally, the aponeuro- sis is continuous posteriorly with the layer of fascia which covers the anterior surfaces of the metacarpals, the interosseous muscles between them, and the ad- ductor pollicis [Fig. 8.8]. Together, these fascial lay- ers surround: (1) the central palmar space; (2) vessels and nerves; (3) long flexor tendons to the fingers;
and (4) the lumbrical muscles which arise from the tendons. Distally, at the level of the heads of the metacarpals, the palmar aponeurosis gives off
digital slips to each of the four fingers [Fig. 8.5]. At this point, sheets of fascia pass from the aponeurosis to the metacarpal fascia. Thus, each digital slip forms a tunnel around the flexor tendons. Nerves, vessels, and lumbrical muscles enter the superficial tissues between these slips. The loose tissue, in which vessels and nerves lie, forms a route for infection to spread from the superficial tissues of the fingers to the central palmar region, from where it can extend behind the flexor retinaculum into the forearm.
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The forearm and hand
Pronator quadratus Pronator quadratus
Brachioradialis
Flexor digitorum profundus Flexor digitorum
superficialis Biceps Supinator Brachialis
Flexor pollicis longus
Supinator Flexor pollicis longus
Flexor digitorum superficialis Pronator teres
Pronator teres
Fig. 8.4 Muscle attachments to the anterior surface of the right radius and ulna.
1st lumbrical
Superficial transverse lig.
4th lumbrical Palmar aponeurosis Flexor digiti minimi Abductor digiti minimi Palmaris brevis Pisiform Flexor retinaculum
Ulnar A.
Flexor carpi ulnaris Flexor carpi radialis
Radial A.
Median N.
Abductor pollicis longus Superficial palmar A.
Opponens pollicis Abductor pollicis brevis Flexor pollicis brevis
Flexor digitorum
superficialis Palmaris longus
Fig. 8.5 Superficial dissection of the palm to show the palmar aponeurosis. The deep fascia has been removed from the thenar and hypothenar eminences.
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Front of the forearm and hand
the distal border of the thenar eminence when the thumb is fully extended.
Branches
The principal branches of the superficial palmar arch are the four palmar digital arteries. The most medial is the proper palmar digital artery to the me- dial side of the little finger. The other three branch- es are the common palmar digital arteries to adjacent sides of two fingers. In the interdigi- tal clefts, the common digital artery receives the corresponding palmar metacarpal artery from the Dissection 8.2 begins the dissection of the palm
of the hand.