EJERCICIO DE EMPRENDIMIENTO
IV. ANÁLISIS O DISCUSIÓN DE RESULTADOS
FLEXOR MUSCLES
The muscles of the second and third groups and the two pronator muscles of the first group comprise the anterior antebrachial muscles. Five of these belong to a superficial layer, and three belong to a deep layer.
Superficial Layer
The muscles of this layer are listed in the order in which they lie from the radial to the ulnar side of the forearm; the flexor digitorum superficialis, however, is deep to the other four muscles:
Middle collateral branch of deep brachial artery
Lateral intermuscular septum chief part of the palmar aponeurosis.
The flexor carpi ulnaris muscle has a humeral and an ulnar head, the humeral head coming from the common flexor tendon. The ulnar head springs from the medial border of the olecranon and the upper two thirds of the posterior border of the ulna. The tendon of the muscle inserts on the pisiform of the wrist and, through it by two ligaments, into the hamulus of the hamate and the base of the fifth metacarpal.
The flexor digitorum superficialis muscle arises by a humeroulnar and a radial head of origin; these are
connected by a fibrous band that crosses the median nerve and the ulnar blood vessels. The larger humer-oulnar head arises from the common tendon, the intermuscular septa, the ulnar collateral ligament, and the medial border of the coronoid process. The radial head is a thin layer arising from the upper two thirds of the anterior border of the radius. The muscle forms two planes; the tendons of its superficial plane pass to the middle and ring fingers, and the deep lamina ends in tendons for digits I and V. These tendons terminate in the palmar aspect of the shafts of the middle phalanges of digits II to V (their relation-ships are described in the discussion of the wrist and hand).
Deep Layer
The deep layer contains the following muscles:
• Flexor digitorum profundus
• Flexor pollicis longus
• Pronator quadratus
The flexor digitorum profundus muscle arises from the posterior border of the ulna (with the flexor carpi ulnaris), the proximal two thirds of the medial surface of the ulna, and adjacent areas of the interosseous mem-brane. The muscle produces, near the wrist, four dis-crete tendons that pass side by side under the flexor retinaculum and dorsal to the tendons of the flexor digitorum superficialis muscle. The tendons terminate on the bases of the distal phalanges of digits II to V. In
M USCLES OF F OREARM (Continued)
Flexor digitorum superficialis muscle (radial head) Anterior branch of medial antebrachial cutaneous nerve Flexor pollicis longus muscle
Interosseous membrane Flexor carpi radialis muscle Ulnar artery and median nerve Palmaris longus muscle
Flexor digitorum superficialis muscle (humeroulnar head) Common interosseous artery
Posterior antebrachial cutaneous nerve (from radial nerve) Palmaris longus muscle
Anterior interosseous artery and nerve (from median nerve)
Ulna and antebrachial fascia
Interosseous membrane and extensor pollicis longus muscle Posterior interosseous artery and nerve
(continuation of deep branch of radial nerve) Palmaris longus tendon
Median nerve
Flexor digitorum superficialis muscle and tendons Flexor carpi ulnaris muscle and tendon
Ulnar artery and nerve Dorsal branch of ulnar nerve
Flexor digitorum profundus muscle and tendons
Extensor digitorum tendons (common tendon to digits 4 and 5 at this level) Radius Extensor digiti minimi tendon
Extensor indicis muscle and tendon
Pronator quadratus muscle and interosseous membrane Extensor carpi ulnaris tendon
Ulna
Antebrachial fascia
Extensor pollicis longus tendon Extensor carpi radialis brevis tendon Extensor carpi radialis longus tendon
Abductor pollicis longus tendon Superficial branch of radial nerve Extensor pollicis brevis tendon Extensor carpi radialis brevis muscle and tendon
Radius Extensor carpi radialis longus muscle and tendon Flexor pollicis longus muscle Radial artery and superficial branch of radial nerve
Brachioradialis muscle Flexor carpi radialis muscle Extensor carpi ulnaris muscle Extensor digiti minimi muscle Extensor digitorum muscle Extensor carpi radialis brevis muscle Extensor carpi radialis longus muscle
Deep branch of radial nerve Supinator muscle Cephalic vein and lateral antebrachial
cutaneous nerve (from musculocutaneous nerve) Brachioradialis muscle
Radius Radial artery and superficial branch of radial nerve
Pronator teres muscle Median antebrachial vein
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OREARMthe palm, the tendons give origin to the small lumbrical muscles.
The flexor pollicis longus muscle arises principally from the anterior surface of the radius (just below its tuberos-ity nearly to the upper border of the pronator quadra-tus) and from the adjacent interosseous membrane. Its tendon, passing between the two sesamoids of the meta-carpophalangeal joint of the thumb, inserts on the base of the distal phalanx of the thumb.
The pronator quadratus muscle is a quadrilateral muscle located just above the wrist and deep to the flexor digitorum profundus and flexor pollicis longus tendons. It arises from the anterior surface of the distal
one fourth of the ulna, its fibers running transversely across the wrist and inserting into the anterior surface of the distal fourth of the shaft of the radius.
EXTENSOR MUSCLES
The muscles of the fourth, fifth, and sixth groups, the supinator muscle of the first group, and the brachiora-dialis muscle make up the posterior antebrachial muscles. Six of these comprise the superficial layer, and five lie in the deep layer.
Superficial Layer
The six muscles of the superficial layer are listed in the order in which they lie across the back of the forearm, from the radial to the ulnar side:
• Brachioradialis
• Extensor carpi radialis longus
• Extensor carpi radialis brevis
• Extensor digitorum
• Extensor digiti minimi
• Extensor carpi ulnaris
As for the flexor muscles, there is a common tendon of origin from the lateral epicondyle for all muscles arising below the lateral epicondyle.
The brachioradialis muscle arises from the upper two thirds of the supracondylar ridge of the humerus. Its tendon appears at about the middle of the forearm and descends to insert into the lateral side of the base of the styloid process of the radius.
The extensor carpi radialis longus muscle arises from the lower third of the supracondylar ridge of the humerus.
M USCLES OF F OREARM (Continued)
1st metacarpal
Radial artery
Interosseous muscles
Radial artery Trapezium
Scaphoid
Hook of hamate
Triquetrum
Flexor carpi ulnaris tendon
Ulnar head Ulnar styloid
Triangular fibrocartilage complex Triangular fibrocartilage
Flexor digitorum superficialis and flexor digitorum profundus tendons
Coronal view
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Scapholunate ligament
Radius Joint capsule
Extensor pollicis brevis and abductor pollicis longus tendons
Pronator quadratus muscle
Lunatotriquetral ligament Ulnar nerve
Ulnar artery
Meniscus homologue
Prestyloid recess (filled with joint fluid) Ulnar collateral ligament
Palmar aponeurosis Transverse carpal ligament Thenar muscle
Trapezoid
Extensor digitorum muscle and tendons Joint capsule
Joint capsule
Radius
Pronator quadratus muscle Flexor digitorum profundus and flexor digitorum superficialis muscles
Flexor pollicis longus tendon Capitate
Interosseous muscles
Lunate Joint capsule Scaphoid
Dorsal radiocarpal ligament Metacarpal 2, base Flexor carpi radialis tendon
Median nerve
Flexor digitorum superficialis tendons
Extensor carpi radialis longus tendon
It has a flat tendon that reaches into the hand to insert on the dorsum of the second metacarpal.
The extensor carpi radialis brevis muscle uses the common tendon of origin for the extensors. Its tendon appears in the lower third of the forearm, closely applied to the overlying tendon of the extensor carpi radialis longus, and inserts on the dorsum of the base of the third metacarpal.
The extensor digitorum muscle also uses the common tendon of origin for the extensors. Above the wrist, it provides four tendons that spread out on the dorsum of the hand, joined side to side in a variable manner by
intertendinous connections. Participating in the rather complex “extensor expansion” described in the section on the wrist and hand, these tendons terminate on the bases of the middle and distal phalanges of digits 2 to 5.
The extensor digiti minimi muscle is a slender muscle that is sometimes only incompletely separated from the extensor digitorum muscle. Its tendon joins the ulnar side of the tendon of the extensor digitorum muscle to the fifth digit for which it provides independent exten-sor action.
The extensor carpi ulnaris muscle arises by the common tendon from the lateral epicondyle but also from the middle one half of the posterior border of the ulna. It inserts on the ulnar side of the base of the fifth metacarpal.
Deep Layer
The muscles of the deep layer are generally submerged under those of the superficial group, although certain of their tendons and parts of their fleshy bellies outcrop just above the wrist:
• Supinator
• Abductor pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
The supinator muscle has a complex origin from the lateral epicondyle of the humerus, the radial collateral ligament, the annular ligament of the radius, and the supinator crest and fossa of the ulna. Its fibers form a flat sheet, directed downward and lateralward, which wraps almost completely around the radius and inserts
M USCLES OF F OREARM (Continued)
Brachioradialis muscle muscles of hand not shown
Flexor carpi ulnaris
on the lateral surface of the upper third of this bone.
As the muscle courses into the posterior compartment of the forearm, it is separated into superficial and deep laminae by the deep branch of the radial nerve.
The abductor pollicis longus muscle lies immediately distal to the supinator. It arises from the middle third of the posterior surface of the radius and the lateral part of the posterior surface of the ulna below the anconeus muscle. The fibers of the muscle converge onto its tendon, which, with the tendon of extensor pollicis brevis closely applied to its medial side, crosses the tendons of the extensor carpi radialis longus and brevis
muscles and inserts on the radial side of the base of the metacarpal of the thumb.
The extensor pollicis brevis muscle, with origins from the radius and the interosseous membrane distal to that of the abductor pollicis longus muscle, inserts on the base of the proximal phalanx of the thumb. It is a spe-cialization of the distal part of the abductor pollicis longus muscle.
The extensor pollicis longus muscle arises from the ulna and the interosseous membrane distal to the abductor pollicis longus muscle. Its tendon passes to the ulnar side of the dorsal tubercle of the radius, then obliquely across the tendons of both radial carpal extensors, ter-minating on the base of the distal phalanx of the thumb.
The extensor indicis muscle arises just below the exten-sor pollicis longus from the ulna and from the interos-seous membrane. In the hand, the tendon joins the ulnar side of the tendon of the digital extensor muscle for the index finger and participates with it in forming the extensor expansion over that digit.
Knowledge of the cross-sectional anatomy of the forearm is critical to understanding advanced imaging views of the forearm as well as surgical anatomy.
Knowing the origins and insertions of the muscles and tendons of the forearm is helpful during operative dis-section and exploration of the forearm and wrist and provides the framework to understanding the func-tional anatomy of the forearm and wrist.