Anatomy_Gray

Anatomy_Gray. Median nerve. The median nerve is formed anterior to the third part of the axillary artery by the union of lateral and medial roots originating from the lateral and medial cords of the brachial plexus (Fig. 7.55). It passes into the arm anterior to the brachial artery and through the arm into the forearm, where branches innervate most of the muscles in the anterior compartment of the forearm (except for the flexor carpi ulnaris muscle and the medial half of the flexor digitorum profundus muscle, which are innervated by the ulnar nerve). The median nerve continues into the hand to innervate: the three thenar muscles associated with the thumb, the two lateral lumbrical muscles associated with movement of the index and middle fingers, and the skin over the palmar surface of the lateral three and one-half digits and over the lateral side of the palm and middle of the wrist.


Anatomy_Gray

Anatomy_Gray. The musculocutaneous nerve, the lateral root of the median nerve, the median nerve, the medial root of the median nerve, and the ulnar nerve form an M over the third part of the axillary artery (Fig. 7.55). This feature, together with penetration of the coracobrachialis muscle by the musculocutaneous nerve, can be used to identify components of the brachial plexus in the axilla. Branches of the posterior cord Five nerves originate from the posterior cord of the brachial plexus: the superior subscapular nerve, the thoracodorsal nerve, the inferior subscapular nerve, the axillary nerve, and the radial nerve (Fig. 7.53). All these nerves except the radial nerve innervate muscles associated with the shoulder region or the posterior wall of the axilla; the radial nerve passes into the arm and forearm.


Anatomy_Gray

Anatomy_Gray. All these nerves except the radial nerve innervate muscles associated with the shoulder region or the posterior wall of the axilla; the radial nerve passes into the arm and forearm. The superior subscapular, thoracodorsal, and inferior subscapular nerves originate sequentially from the posterior cord and pass directly into muscles associated with the posterior axillary wall (Fig. 7.56). The superior subscapular nerve is short and passes into and supplies the subscapularis muscle. The thoracodorsal nerve is the longest of these three nerves and passes vertically along the posterior axillary wall. It penetrates and innervates the latissimus dorsi muscle. The inferior subscapular nerve also passes inferiorly along the posterior axillary wall and innervates the subscapularis and teres major muscles.


Anatomy_Gray

Anatomy_Gray. The axillary nerve originates from the posterior cord and passes inferiorly and laterally along the posterior wall to exit the axilla through the quadrangular space (Fig. 7.56). It passes posteriorly around the surgical neck of the humerus and innervates both the deltoid and teres minor muscles. A superior lateral cutaneous nerve of the arm originates from the axillary nerve after passing through the quadrangular space and loops around the posterior margin of the deltoid muscle to innervate skin in that region. The axillary nerve is accompanied by the posterior circumflex humeral artery.


Anatomy_Gray

Anatomy_Gray. The radial nerve is the largest terminal branch of the posterior cord (Fig. 7.56). It passes out of the axilla and into the posterior compartment of the arm by passing through the triangular interval between the inferior border of the teres major muscle, the long head of the triceps brachii muscle, and the shaft of the humerus. It is accompanied through the triangular interval by the profunda brachii artery, which originates from the brachial artery in the anterior compartment of the arm. The radial nerve and its branches innervate: all muscles in the posterior compartments of the arm and forearm, and the skin on the posterior aspect of the arm and forearm, the lower lateral surface of the arm, and the dorsal lateral surface of the hand. The posterior cutaneous nerve of the arm (posterior brachial cutaneous nerve) originates from the radial nerve in the axilla and innervates skin on the posterior surface of the arm.


Anatomy_Gray

Anatomy_Gray. The posterior cutaneous nerve of the arm (posterior brachial cutaneous nerve) originates from the radial nerve in the axilla and innervates skin on the posterior surface of the arm. All lymphatics from the upper limb drain into lymph nodes in the axilla (Fig. 7.57). In addition, axillary nodes receive drainage from an extensive area on the adjacent trunk, which includes regions of the upper back and shoulder, the lower neck, the chest, and the upper anterolateral abdominal wall. Axillary nodes also receive drainage from approximately 75% of the mammary gland. The 20–30 axillary nodes are generally divided into five groups on the basis of location. Humeral (lateral) nodes posteromedial to the axillary vein receive most of the lymphatic drainage from the upper limb. Pectoral (anterior) nodes occur along the inferior margin of the pectoralis minor muscle along the course of the lateral thoracic vessels and receive drainage from the abdominal wall, the chest, and the mammary gland.


Anatomy_Gray

Anatomy_Gray. Subscapular (posterior) nodes on the posterior axillary wall in association with the subscapular vessels drain the posterior axillary wall and receive lymphatics from the back, the shoulder, and the neck. Central nodes are embedded in axillary fat and receive tributaries from humeral, subscapular, and pectoral groups of nodes. Apical nodes are the most superior group of nodes in the axilla and drain all other groups of nodes in the region. In addition, they receive lymphatic vessels that accompany the cephalic vein as well as vessels that drain the superior region of the mammary gland. Efferent vessels from the apical group converge to form the subclavian trunk, which usually joins the venous system at the junction between the right subclavian vein and the right internal jugular vein in the neck. On the left, the subclavian trunk usually joins the thoracic duct in the base of the neck. Axillary process of the mammary gland


Anatomy_Gray

Anatomy_Gray. Axillary process of the mammary gland Although the mammary gland is in superficial fascia overlying the thoracic wall, its superolateral region extends along the inferior margin of the pectoralis major muscle toward the axilla. In some cases, this may pass around the margin of the muscle to penetrate deep fascia and enter the axilla (Fig. 7.58). This axillary process rarely reaches as high as the apex of the axilla. The arm is the region of the upper limb between the shoulder and the elbow (Fig. 7.59). The superior aspect of the arm communicates medially with the axilla. Inferiorly, a number of important structures pass between the arm and the forearm through the cubital fossa, which is positioned anterior to the elbow joint. The arm is divided into two compartments by medial and lateral intermuscular septa, which pass from each side of the humerus to the outer sleeve of deep fascia that surrounds the limb (Fig. 7.59).


Anatomy_Gray

Anatomy_Gray. The arm is divided into two compartments by medial and lateral intermuscular septa, which pass from each side of the humerus to the outer sleeve of deep fascia that surrounds the limb (Fig. 7.59). The anterior compartment of the arm contains muscles that predominantly flex the elbow joint; the posterior compartment contains muscles that extend the joint. Major nerves and vessels supply and pass through each compartment. The skeletal support for the arm is the humerus (Fig. 7.60). Most of the large muscles of the arm insert into the proximal ends of the two bones of the forearm, the radius and the ulna, and flex and extend the forearm at the elbow joint. In addition, the muscles predominantly situated in the forearm that move the hand originate at the distal end of the humerus. Shaft and distal end of the humerus


Anatomy_Gray

Anatomy_Gray. Shaft and distal end of the humerus In cross section, the shaft of the humerus is somewhat triangular with: anterior, lateral, and medial borders, and anterolateral, anteromedial, and posterior surfaces (Fig. 7.60). The posterior surface of the humerus is marked on its superior aspect by a linear roughening for the attachment of the lateral head of the triceps brachii muscle, beginning just inferior to the surgical neck and passing diagonally across the bone to the deltoid tuberosity. The middle part of the posterior surface and adjacent part of the anterolateral surface are marked by the shallow radial groove, which passes diagonally down the bone and parallel to the sloping posterior margin of the deltoid tuberosity. The radial nerve and the profunda brachii artery lie in this groove. Approximately in the middle of the shaft, the medial border is marked by thin elongate roughening for the attachment of the coracobrachialis muscle.


Anatomy_Gray

Anatomy_Gray. Approximately in the middle of the shaft, the medial border is marked by thin elongate roughening for the attachment of the coracobrachialis muscle. Intermuscular septa, which separate the anterior compartment from the posterior compartment, attach to the medial and lateral borders (Fig. 7.61). Distally, the bone becomes flattened, and these borders expand as the lateral supraepicondylar ridge (lateral supracondylar ridge) and the medial supraepicondylar ridge (medial supracondylar ridge). The lateral supraepicondylar ridge is more pronounced than the medial ridge and is roughened for the attachment of muscles found in the posterior compartment of the forearm. The distal end of the humerus, which is flattened in the anteroposterior plane, bears a condyle, two epicondyles, and three fossae, as follows (Fig. 7.61). The condyle The two articular parts of the condyle, the capitulum and the trochlea, articulate with the two bones of the forearm.


Anatomy_Gray

Anatomy_Gray. The condyle The two articular parts of the condyle, the capitulum and the trochlea, articulate with the two bones of the forearm. The capitulum articulates with the radius of the forearm. Lateral in position and hemispherical in shape, it projects anteriorly and somewhat inferiorly and is not visible when the humerus is viewed from the posterior aspect. The trochlea articulates with the ulna of the forearm. It is pulley shaped and lies medial to the capitulum. Its medial edge is more pronounced than its lateral edge and, unlike the capitulum, it extends onto the posterior surface of the bone. The two epicondyles The two epicondyles lie adjacent, and somewhat superior, to the trochlea and capitulum (Fig. 7.61).


Anatomy_Gray

Anatomy_Gray. The two epicondyles The two epicondyles lie adjacent, and somewhat superior, to the trochlea and capitulum (Fig. 7.61). The medial epicondyle, a large bony protuberance, is the major palpable landmark on the medial side of the elbow, and projects medially from the distal end of the humerus. On its surface, it bears a large oval impression for the attachment of muscles in the anterior compartment of the forearm. The ulnar nerve passes from the arm into the forearm around the posterior surface of the medial epicondyle and can be palpated against the bone in this location. The lateral epicondyle is much less pronounced than the medial epicondyle. It is lateral to the capitulum and has a large irregular impression for the attachment of muscles in the posterior compartment of the forearm. The three fossae Three fossae occur superior to the trochlea and capitulum on the distal end of the humerus (Fig. 7.61).


Anatomy_Gray

Anatomy_Gray. The three fossae Three fossae occur superior to the trochlea and capitulum on the distal end of the humerus (Fig. 7.61). The radial fossa is the least distinct of the fossae and occurs immediately superior to the capitulum on the anterior surface of the humerus. The coronoid fossa is adjacent to the radial fossa and is superior to the trochlea. The largest of the fossae, the olecranon fossa, occurs immediately superior to the trochlea on the posterior surface of the distal end of the humerus. These three fossae accommodate projections from the bones in the forearm during movements of the elbow joint. Proximal end of the radius The proximal end of the radius consists of a head, a neck, and the radial tuberosity (Fig. 7.62A,B).


Anatomy_Gray

Anatomy_Gray. Proximal end of the radius The proximal end of the radius consists of a head, a neck, and the radial tuberosity (Fig. 7.62A,B). The head of the radius is a thick disc-shaped structure oriented in the horizontal plane. The circular superior surface is concave for articulation with the capitulum of the humerus. The thick margin of the disc is broad medially where it articulates with the radial notch on the proximal end of the ulna. The neck of the radius is a short and narrow cylinder of bone between the expanded head and the radial tuberosity on the shaft. The radial tuberosity is a large blunt projection on the medial surface of the radius immediately inferior to the neck. Much of its surface is roughened for the attachment of the biceps brachii tendon. The oblique line of the radius continues diagonally across the shaft of the bone from the inferior margin of the radial tuberosity. Proximal end of the ulna


Anatomy_Gray

Anatomy_Gray. Proximal end of the ulna The proximal end of the ulna is much larger than the proximal end of the radius and consists of the olecranon, the coronoid process, the trochlear notch, the radial notch, and the tuberosity of the ulna (Fig. 7.63A,B). The olecranon is a large projection of bone that extends proximally from the ulna. Its anterolateral surface is articular and contributes to the formation of the trochlear notch, which articulates with the trochlea of the humerus. The superior surface is marked by a large roughened impression for the attachment of the triceps brachii muscle. The posterior surface is smooth, shaped somewhat triangularly, and can be palpated as the “tip of the elbow.” The coronoid process projects anteriorly from the proximal end of the ulna (Fig. 7.63). Its superolateral surface is articular and participates, with the olecranon, in forming the trochlear notch. The lateral surface is marked by the radial notch for articulation with the head of the radius.


Anatomy_Gray

Anatomy_Gray. Just inferior to the radial notch is a fossa that allows the radial tuberosity to change position during pronation and supination. The posterior margin of this fossa is broadened to form the supinator crest. The anterior surface of the coronoid process is triangular, with the apex directed distally, and has a number of roughenings for muscle attachment. The largest of these roughenings, the tuberosity of the ulna, is at the apex of the anterior surface and is the attachment site for the brachialis muscle. The anterior compartment of the arm contains three muscles—the coracobrachialis, brachialis, and biceps brachii muscles—which are innervated predominantly by the musculocutaneous nerve. The posterior compartment contains one muscle—the triceps brachii muscle—which is innervated by the radial nerve.


Anatomy_Gray

Anatomy_Gray. The posterior compartment contains one muscle—the triceps brachii muscle—which is innervated by the radial nerve. The coracobrachialis muscle extends from the tip of the coracoid process of the scapula to the medial side of the midshaft of the humerus (Fig. 7.64 and Table 7.8). It passes through the axilla and is penetrated and innervated by the musculocutaneous nerve. The coracobrachialis muscle flexes the arm. The biceps brachii muscle has two heads: The short head of the muscle originates from the coracoid process in conjunction with the coracobrachialis. The long head originates as a tendon from the supraglenoid tubercle of the scapula (Fig. 7.64 and Table 7.8). The tendon of the long head passes through the glenohumeral joint superior to the head of the humerus and then passes through the intertubercular sulcus and enters the arm. In the arm, the tendon joins with its muscle belly and, together with the muscle belly of the short head, overlies the brachialis muscle.


Anatomy_Gray

Anatomy_Gray. The long and short heads converge to form a single tendon, which inserts onto the radial tuberosity. As the tendon enters the forearm, a flat sheet of connective tissue (the bicipital aponeurosis) fans out from the medial side of the tendon to blend with deep fascia covering the anterior compartment of the forearm. The biceps brachii muscle is a powerful flexor of the forearm at the elbow joint; it is also the most powerful supinator of the forearm when the elbow joint is flexed. Because the two heads of the biceps brachii muscle cross the glenohumeral joint, the muscle can also flex the glenohumeral joint. The biceps brachii muscle is innervated by the musculocutaneous nerve. A tap on the tendon of the biceps brachii at the elbow is used to test predominantly spinal cord segment C6.


Anatomy_Gray

Anatomy_Gray. The biceps brachii muscle is innervated by the musculocutaneous nerve. A tap on the tendon of the biceps brachii at the elbow is used to test predominantly spinal cord segment C6. The brachialis muscle originates from the distal half of the anterior aspect of the humerus and from adjacent parts of the intermuscular septa, particularly on the medial side (Fig. 7.64 and Table 7.8). It lies beneath the biceps brachii muscle, is flattened dorsoventrally, and converges to form a tendon, which attaches to the tuberosity of the ulna. The brachialis muscle flexes the forearm at the elbow joint. Innervation of the brachialis muscle is predominantly by the musculocutaneous nerve. A small component of the lateral part is innervated by the radial nerve. The only muscle of the posterior compartment of the arm is the triceps brachii muscle (Fig. 7.65 and Table 7.9). The triceps brachii muscle has three heads: The long head originates from the infraglenoid tubercle of the scapula.


Anatomy_Gray

Anatomy_Gray. The long head originates from the infraglenoid tubercle of the scapula. The medial head originates from the extensive area on the posterior surface of the shaft of the humerus inferior to the radial groove. The lateral head originates from a linear roughening superior to the radial groove of the humerus. The three heads converge to form a large tendon, which inserts on the superior surface of the olecranon of the ulna. The triceps brachii muscle extends the forearm at the elbow joint. Innervation of the triceps brachii is by branches of the radial nerve. A tap on the tendon of the triceps brachii tests predominantly spinal cord segment C7. The major artery of the arm, the brachial artery, is found in the anterior compartment (Fig. 7.66A). Beginning as a continuation of the axillary artery at the lower border of the teres major muscle, it terminates just distal to the elbow joint where it divides into the radial and ulnar arteries.


Anatomy_Gray

Anatomy_Gray. In the proximal arm, the brachial artery lies on the medial side. In the distal arm, it moves laterally to assume a position midway between the lateral epicondyle and the medial epicondyle of the humerus. It crosses anteriorly to the elbow joint where it lies immediately medial to the tendon of the biceps brachii muscle. The brachial artery is palpable along its length. In proximal regions, the brachial artery can be compressed against the medial side of the humerus. Branches of the brachial artery in the arm include those to adjacent muscles and two ulnar collateral vessels, which contribute to a network of arteries around the elbow joint (Fig. 7.66B). Additional branches are the profunda brachii artery and nutrient arteries to the humerus, which pass through a foramen in the anteromedial surface of the humeral shaft.


Anatomy_Gray

Anatomy_Gray. The profunda brachii artery, the largest branch of the brachial artery, passes into and supplies the posterior compartment of the arm (Fig. 7.66A,B). It enters the posterior compartment with the radial nerve and together they pass through the triangular interval, which is formed by the shaft of the humerus, the inferior margin of the teres major muscle, and the lateral margin of the long head of the triceps muscle. They then pass along the radial groove on the posterior surface of the humerus deep to the lateral head of the triceps brachii muscle. Branches of the profunda brachii artery supply adjacent muscles and anastomose with the posterior circumflex humeral artery. The artery terminates as two collateral vessels, which contribute to an anastomotic network of arteries around the elbow joint (Fig. 7.66B). Paired brachial veins pass along the medial and lateral sides of the brachial artery, receiving tributaries that accompany branches of the artery (Fig. 7.67).


Anatomy_Gray

Anatomy_Gray. Paired brachial veins pass along the medial and lateral sides of the brachial artery, receiving tributaries that accompany branches of the artery (Fig. 7.67). In addition to these deep veins, two large subcutaneous veins, the basilic vein and the cephalic vein, are located in the arm. The basilic vein passes vertically in the distal half of the arm, penetrates deep fascia to assume a position medial to the brachial artery, and then becomes the axillary vein at the lower border of the teres major muscle. The brachial veins join the basilic, or axillary, vein. The cephalic vein passes superiorly on the anterolateral aspect of the arm and through the anterior wall of the axilla to reach the axillary vein.


Anatomy_Gray

Anatomy_Gray. The cephalic vein passes superiorly on the anterolateral aspect of the arm and through the anterior wall of the axilla to reach the axillary vein. The musculocutaneous nerve leaves the axilla and enters the arm by passing through the coracobrachialis muscle (Fig. 7.68). It passes diagonally down the arm in the plane between the biceps brachii and brachialis muscles. After giving rise to motor branches in the arm, it emerges laterally to the tendon of the biceps brachii muscle at the elbow, penetrates deep fascia, and continues as the lateral cutaneous nerve of the forearm. The musculocutaneous nerve provides: motor innervation to all muscles in the anterior compartment of the arm, and sensory innervation to skin on the lateral surface of the forearm.


Anatomy_Gray

Anatomy_Gray. The musculocutaneous nerve provides: motor innervation to all muscles in the anterior compartment of the arm, and sensory innervation to skin on the lateral surface of the forearm. The median nerve enters the arm from the axilla at the inferior margin of the teres major muscle (Fig. 7.68). It passes vertically down the medial side of the arm in the anterior compartment and is related to the brachial artery throughout its course: In proximal regions, the median nerve is immediately lateral to the brachial artery. In more distal regions, the median nerve crosses to the medial side of the brachial artery and lies anterior to the elbow joint. The median nerve has no major branches in the arm, but a branch to one of the muscles of the forearm, the pronator teres muscle, may originate from the nerve immediately proximal to the elbow joint.


Anatomy_Gray

Anatomy_Gray. The median nerve has no major branches in the arm, but a branch to one of the muscles of the forearm, the pronator teres muscle, may originate from the nerve immediately proximal to the elbow joint. The ulnar nerve enters the arm with the median nerve and axillary artery (Fig. 7.68). It passes through proximal regions medial to the axillary artery. In the middle of the arm, the ulnar nerve penetrates the medial intermuscular septum and enters the posterior compartment where it lies anterior to the medial head of the triceps brachii muscle. It passes posterior to the medial epicondyle of the humerus and then into the anterior compartment of the forearm. The ulnar nerve has no major branches in the arm.


Anatomy_Gray

Anatomy_Gray. The ulnar nerve has no major branches in the arm. The radial nerve originates from the posterior cord of the brachial plexus and enters the arm by crossing the inferior margin of the teres major muscle (Fig. 7.69). As it enters the arm, it lies posterior to the brachial artery. Accompanied by the profunda brachii artery, the radial nerve enters the posterior compartment of the arm by passing through the triangular interval.


Anatomy_Gray

Anatomy_Gray. As the radial nerve passes diagonally, from medial to lateral, through the posterior compartment, it lies in the radial groove directly on bone. On the lateral side of the arm, it passes anteriorly through the lateral intermuscular septum and enters the anterior compartment where it lies between the brachialis muscle and a muscle of the posterior compartment of the forearm—the brachioradialis muscle, which attaches to the lateral supraepicondylar ridge of the humerus. The radial nerve enters the forearm anterior to the lateral epicondyle of the humerus, just deep to the brachioradialis muscle. In the arm, the radial nerve has muscular and cutaneous branches (Fig. 7.69).


Anatomy_Gray

Anatomy_Gray. In the arm, the radial nerve has muscular and cutaneous branches (Fig. 7.69). Muscular branches include those to the triceps brachii, brachioradialis, and extensor carpi radialis longus muscles. In addition, the radial nerve contributes to the innervation of the lateral part of the brachialis muscle. One of the branches to the medial head of the triceps brachii muscle arises before the radial nerve’s entrance into the posterior compartment and passes vertically down the arm in association with the ulnar nerve. Cutaneous branches of the radial nerve that originate in the posterior compartment of the arm are the inferior lateral cutaneous nerve of the arm and the posterior cutaneous nerve of the forearm, both of which penetrate through the lateral head of the triceps brachii muscle and the overlying deep fascia to become subcutaneous. The elbow joint is a complex joint involving three separate articulations, which share a common synovial cavity (Fig. 7.71).


Anatomy_Gray

Anatomy_Gray. The elbow joint is a complex joint involving three separate articulations, which share a common synovial cavity (Fig. 7.71). The joints between the trochlear notch of the ulna and the trochlea of the humerus and between the head of the radius and the capitulum of the humerus are primarily involved with hinge-like flexion and extension of the forearm on the arm and, together, are the principal articulations of the elbow joint. The joint between the head of the radius and the radial notch of the ulna, the proximal radio-ulnar joint, is involved with pronation and supination of the forearm. The articular surfaces of the bones are covered with hyaline cartilage. The synovial membrane originates from the edges of the articular cartilage and lines the radial fossa, the coronoid fossa, the olecranon fossa, the deep surface of the joint capsule, and the medial surface of the trochlea (Fig. 7.72).


Anatomy_Gray

Anatomy_Gray. The synovial membrane is separated from the fibrous membrane of the joint capsule by pads of fat in regions overlying the coronoid fossa, the olecranon fossa, and the radial fossa. These fat pads accommodate the related bony processes during extension and flexion of the elbow. Attachments of the brachialis and triceps brachii muscles to the joint capsule overlying these regions pull the attached fat pads out of the way when the adjacent bony processes are moved into the fossae. The fibrous membrane of the joint capsule overlies the synovial membrane, encloses the joint, and attaches to the medial epicondyle and the margins of the olecranon, coronoid, and radial fossae of the humerus (Fig. 7.73). It also attaches to the coronoid process and olecranon of the ulna. On the lateral side, the free inferior margin of the joint capsule passes around the neck of the radius from an anterior attachment to the coronoid process of the ulna to a posterior attachment to the base of the olecranon.


Anatomy_Gray

Anatomy_Gray. The fibrous membrane of the joint capsule is thickened medially and laterally to form collateral ligaments, which support the flexion and extension movements of the elbow joint (Fig. 7.73). In addition, the external surface of the joint capsule is reinforced laterally where it cuffs the head of the radius with a strong anular ligament of the radius. Although this ligament blends with the fibrous membrane of the joint capsule in most regions, they are separate posteriorly. The anular ligament of the radius also blends with the radial collateral ligament. The anular ligament of the radius and related joint capsule allow the radial head to slide against the radial notch of the ulna and pivot on the capitulum during pronation and supination of the forearm.


Anatomy_Gray

Anatomy_Gray. The deep surface of the fibrous membrane of the joint capsule and the related anular ligament of the radius that articulate with the sides of the radial head are lined by cartilage. A pocket of synovial membrane (sacciform recess) protrudes from the inferior free margin of the joint capsule and facilitates rotation of the radial head during pronation and supination. Vascular supply to the elbow joint is through an anastomotic network of vessels derived from collateral and recurrent branches of the brachial, profunda brachii, radial, and ulnar arteries. The elbow joint is innervated predominantly by branches of the radial and musculocutaneous nerves, but there may be some innervation by branches of the ulnar and median nerves.


Anatomy_Gray

Anatomy_Gray. The elbow joint is innervated predominantly by branches of the radial and musculocutaneous nerves, but there may be some innervation by branches of the ulnar and median nerves. The cubital fossa is an important area of transition between the arm and the forearm. It is located anterior to the elbow joint and is a triangular depression formed between two forearm muscles: the brachioradialis muscle originating from the lateral supra-epicondylar ridge of the humerus, and the pronator teres muscle originating from the medial epicondyle of the humerus (Fig. 7.77A). The base of the triangle is an imaginary horizontal line between the medial and lateral epicondyles. The bed or floor of the fossa is formed mainly by the brachialis muscle. The major contents of the cubital fossa, from lateral to medial, are: the tendon of the biceps brachii muscle, the brachial artery, and the median nerve (Fig. 7.77B).


Anatomy_Gray

Anatomy_Gray. The major contents of the cubital fossa, from lateral to medial, are: the tendon of the biceps brachii muscle, the brachial artery, and the median nerve (Fig. 7.77B). The brachial artery normally bifurcates into the radial and ulnar arteries in the apex of the fossa (Fig. 7.77B), although this bifurcation may occur much higher in the arm, even in the axilla. When taking a blood pressure reading from a patient, the clinician places the stethoscope over the brachial artery in the cubital fossa. The median nerve lies immediately medial to the brachial artery and leaves the fossa by passing between the ulnar and humeral heads of the pronator teres muscle (Fig. 7.77C).


Anatomy_Gray

Anatomy_Gray. The median nerve lies immediately medial to the brachial artery and leaves the fossa by passing between the ulnar and humeral heads of the pronator teres muscle (Fig. 7.77C). The brachial artery and the median nerve are covered and protected anteriorly in the distal part of the cubital fossa by the bicipital aponeurosis (Fig. 7.77B). This flat connective tissue membrane passes between the medial side of the tendon of the biceps brachii muscle and deep fascia of the forearm. The sharp medial margin of the bicipital aponeurosis can often be felt. The radial nerve lies just under the lip of the brachioradialis muscle, which forms the lateral margin of the fossa (Fig. 7.77C). In this position, the radial nerve divides into superficial and deep branches: The superficial branch continues into the forearm just deep to the brachioradialis muscle.


Anatomy_Gray

Anatomy_Gray. The superficial branch continues into the forearm just deep to the brachioradialis muscle. The deep branch passes between the two heads of the supinator muscle (see pp. 778–780 and Fig. 7.92) to access the posterior compartment of the forearm. The ulnar nerve does not pass through the cubital fossa. Instead, it passes posterior to the medial epicondyle. The roof of the cubital fossa is formed by superficial fascia and skin. The most important structure within the roof is the median cubital vein (Fig. 7.77D), which passes diagonally across the roof and connects the cephalic vein on the lateral side of the upper limb with the basilic vein on the medial side. The bicipital aponeurosis separates the median cubital vein from the brachial artery and median nerve. Other structures within the roof are cutaneous nerves—the medial cutaneous and lateral cutaneous nerves of the forearm.


Anatomy_Gray

Anatomy_Gray. The forearm is the part of the upper limb that extends between the elbow joint and the wrist joint. Proximally, most major structures pass between the arm and forearm through, or in relation to, the cubital fossa, which is anterior to the elbow joint (Fig. 7.79). The exception is the ulnar nerve, which passes posterior to the medial epicondyle of the humerus. Distally, structures pass between the forearm and the hand through, or anterior to, the carpal tunnel (Fig. 7.79). The major exception is the radial artery, which passes dorsally around the wrist to enter the hand posteriorly. The bone framework of the forearm consists of two parallel bones, the radius and the ulna (Figs. 7.79 and 7.80B). The radius is lateral in position and is small proximally, where it articulates with the humerus, and large distally, where it forms the wrist joint with the carpal bones of the hand.


Anatomy_Gray

Anatomy_Gray. The ulna is medial in the forearm, and its proximal and distal dimensions are the reverse of those for the radius: the ulna is large proximally and small distally. Proximal and distal joints between the radius and the ulna allow the distal end of the radius to swing over the adjacent end of the ulna, resulting in pronation and supination of the hand. As in the arm, the forearm is divided into anterior and posterior compartments (Fig. 7.79). In the forearm, these compartments are separated by: a lateral intermuscular septum, which passes from the anterior border of the radius to deep fascia surrounding the limb; an interosseous membrane, which links adjacent borders of the radius and ulna along most of their length; and the attachment of deep fascia along the posterior border of the ulna.


Anatomy_Gray

Anatomy_Gray. Muscles in the anterior compartment of the forearm flex the wrist and digits and pronate the hand. Muscles in the posterior compartment extend the wrist and digits and supinate the hand. Major nerves and vessels supply or pass through each compartment. Shaft and distal end of radius The shaft of the radius is narrow proximally, where it is continuous with the radial tuberosity and neck, and much broader distally, where it expands to form the distal end (Fig. 7.80). Throughout most of its length, the shaft of the radius is triangular in cross section, with: three borders (anterior, posterior, and interosseous), and three surfaces (anterior, posterior, and lateral).


Anatomy_Gray

Anatomy_Gray. The anterior border begins on the medial side of the bone as a continuation of the radial tuberosity. In the superior third of the bone, it crosses the shaft diagonally, from medial to lateral, as the oblique line of the radius. The posterior border is distinct only in the middle third of the bone. The interosseous border is sharp and is the attachment site for the interosseous membrane, which links the radius to the ulna. The anterior and posterior surfaces of the radius are generally smooth, whereas an oval roughening for the attachment of the pronator teres marks approximately the middle of the lateral surface of the radius. Viewed anteriorly, the distal end of the radius is broad and somewhat flattened anteroposteriorly (Fig. 7.80). Consequently, the radius has expansive anterior and posterior surfaces and narrow medial and lateral surfaces. Its anterior surface is smooth and unremarkable, except for the prominent sharp ridge that forms its lateral margin.


Anatomy_Gray

Anatomy_Gray. The posterior surface of the radius is characterized by the presence of a large dorsal tubercle, which acts as a pulley for the tendon of one of the extensor muscles of the thumb (extensor pollicis longus). The medial surface is marked by a prominent facet for articulation with the distal end of the ulna (Fig. 7.80). The lateral surface of the radius is diamond shaped and extends distally as a radial styloid process. The distal end of the bone is marked by two facets for articulation with two carpal bones (the scaphoid and lunate). Shaft and distal end of ulna The shaft of the ulna is broad superiorly where it is continuous with the large proximal end and narrow distally to form a small distal head (Fig. 7.81). Like the radius, the shaft of the ulna is triangular in cross section and has: three borders (anterior, posterior, and interosseous), and three surfaces (anterior, posterior, and medial).


Anatomy_Gray

Anatomy_Gray. The anterior border is smooth and rounded. The posterior border is sharp and palpable along its entire length. The interosseous border is also sharp and is the attachment site for the interosseous membrane, which joins the ulna to the radius. The anterior surface of the ulna is smooth, except distally where there is a prominent linear roughening for the attachment of the pronator quadratus muscle. The medial surface is smooth and unremarkable. The posterior surface is marked by lines, which separate different regions of muscle attachments to bone. The distal end of the ulna is small and characterized by a rounded head and the ulnar styloid process (Fig. 7.81). The anterolateral and distal part of the head is covered by articular cartilage. The ulnar styloid process originates from the posteromedial aspect of the ulna and projects distally.


Anatomy_Gray

Anatomy_Gray. The distal radio-ulnar joint occurs between the articular surface of the head of the ulna, with the ulnar notch on the end of the radius, and with a fibrous articular disc, which separates the radio-ulnar joint from the wrist joint (Fig. 7.82). The triangular-shaped articular disc is attached by its apex to a roughened depression on the ulna between the styloid process and the articular surface of the head, and by its base to the angular margin of the radius between the ulnar notch and the articular surface for the carpal bones. The synovial membrane is attached to the margins of the distal radio-ulnar joint and is covered on its external surface by a fibrous joint capsule. The distal radio-ulnar joint allows the distal end of the radius to move anteromedially over the ulna.


Anatomy_Gray

Anatomy_Gray. The distal radio-ulnar joint allows the distal end of the radius to move anteromedially over the ulna. The interosseous membrane is a thin fibrous sheet that connects the medial and lateral borders of the radius and ulna, respectively (Fig. 7.82). Collagen fibers within the sheet pass predominantly inferiorly from the radius to the ulna. The interosseous membrane has a free upper margin, which is situated just inferior to the radial tuberosity, and a small circular aperture in its distal third. Vessels pass between the anterior and posterior compartments superior to the upper margin and through the inferior aperture. The interosseous membrane connects the radius and ulna without restricting pronation and supination and provides attachment for muscles in the anterior and posterior compartments. The orientation of fibers in the membrane is also consistent with its role in transferring forces from the radius to the ulna and ultimately, therefore, from the hand to the humerus.


Anatomy_Gray

Anatomy_Gray. Pronation and supination of the hand occur entirely in the forearm and involve rotation of the radius at the elbow and movement of the distal end of the radius over the ulna (Fig. 7.83). At the elbow, the superior articular surface of the radial head spins on the capitulum while, at the same time, the articular surface on the side of the head slides against the radial notch of the ulna and adjacent areas of the joint capsule and anular ligament of the radius. At the distal radio-ulnar joint, the ulnar notch of the radius slides anteriorly over the convex surface of the head of the ulna. During these movements, the bones are held together by: the anular ligament of the radius at the proximal radio-ulnar joint, the interosseous membrane along the lengths of the radius and ulna, and the articular disc at the distal radio-ulnar joint (Fig. 7.83).


Anatomy_Gray

Anatomy_Gray. Because the hand articulates predominantly with the radius, the translocation of the distal end of the radius medially over the ulna moves the hand from the palm-anterior (supinated) position to the palm-posterior (pronated) position. Two muscles supinate and two muscles pronate the hand (Fig. 7.83). Biceps brachii. The biceps brachii muscle, the largest of the four muscles that supinate and pronate the hand, is a powerful supinator as well as a flexor of the elbow joint. It is most effective as a supinator when the forearm is flexed. Supinator. The second of the muscles involved with supination is the supinator muscle. Located in the posterior compartment of the forearm, it has a broad origin, from the supinator crest of the ulna and the lateral epicondyle of the humerus and from ligaments associated with the elbow joint.


Anatomy_Gray

Anatomy_Gray. The supinator muscle curves around the posterior surface and the lateral surface of the upper third of the radius to attach to the shaft of the radius superior to the oblique line. The tendon of the biceps brachii muscle and the supinator muscle both become wrapped around the proximal end of the radius when the hand is pronated (Fig. 7.83). When they contract, they unwrap from the bone, producing supination of the hand. Pronator teres and pronator quadratus. Pronation results from the action of the pronator teres and pronator quadratus muscles (Fig. 7.83). Both these muscles are in the anterior compartment of the forearm: The pronator teres runs from the medial epicondyle of the humerus to the lateral surface of the radius, approximately midway along the shaft. The pronator quadratus extends between the anterior surfaces of the distal ends of the radius and ulna.


Anatomy_Gray

Anatomy_Gray. The pronator quadratus extends between the anterior surfaces of the distal ends of the radius and ulna. When these muscles contract, they pull the distal end of the radius over the ulna, resulting in pronation of the hand (Fig. 7.83). Anconeus. In addition to hinge-like flexion and extension at the elbow joint, some abduction of the distal end of the ulna also occurs and maintains the position of the palm of the hand over a central axis during pronation (Fig. 7.84). The muscle involved in this movement is the anconeus muscle, which is a triangular muscle in the posterior compartment of the forearm that runs from the lateral epicondyle to the lateral surface of the proximal end of the ulna. Muscles in the anterior (flexor) compartment of the forearm occur in three layers: superficial, intermediate, and deep. Generally, these muscles are associated with: movements of the wrist joint, flexion of the fingers including the thumb, and pronation.


Anatomy_Gray

Anatomy_Gray. All muscles in the anterior compartment of the forearm are innervated by the median nerve, except for the flexor carpi ulnaris muscle and the medial half of the flexor digitorum profundus muscle, which are innervated by the ulnar nerve. All four muscles in the superficial layer—the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres—have a common origin from the medial epicondyle of the humerus, and, except for the pronator teres, extend distally from the forearm into the hand (Fig. 7.85 and Table 7.10). The flexor carpi ulnaris muscle is the most medial of the muscles in the superficial layer of flexors, having a long linear origin from the olecranon and posterior border of the ulna, in addition to an origin from the medial epicondyle of the humerus (Fig. 7.85A,B).


Anatomy_Gray

Anatomy_Gray. The ulnar nerve enters the anterior compartment of the forearm by passing through the triangular gap between the humeral and ulnar heads of the flexor carpi ulnaris (Fig. 7.85B). The muscle fibers converge on a tendon that passes distally and attaches to the pisiform bone of the wrist. From this point, force is transferred to the hamate bone of the wrist and to the base of metacarpal V by the pisohamate and pisometacarpal ligaments. The flexor carpi ulnaris muscle is a powerful flexor and adductor of the wrist and is innervated by the ulnar nerve (Table 7.10). The palmaris longus muscle, which is absent in about 15% of the population, lies between the flexor carpi ulnaris and the flexor carpi radialis muscles (Fig. 7.85A). It is a spindle-shaped muscle with a long tendon, which passes into the hand and attaches to the flexor retinaculum and to a thick layer of deep fascia, the palmar aponeurosis, which underlies and is attached to the skin of the palm and fingers.


Anatomy_Gray

Anatomy_Gray. In addition to its role as an accessory flexor of the wrist joint, the palmaris longus muscle also opposes shearing forces on the skin of the palm during gripping (Table 7.10). The flexor carpi radialis muscle is lateral to the palmaris longus and has a large and prominent tendon in the distal half of the forearm (Fig. 7.85A and Table 7.10). Unlike the tendon of the flexor carpi ulnaris, which forms the medial margin of the distal forearm, the tendon of the flexor carpi radialis muscle is positioned just lateral to the midline. In this position, the tendon can be easily palpated, making it an important landmark for finding the pulse in the radial artery, which lies immediately lateral to it. The tendon of the flexor carpi radialis passes through a compartment formed by bone and fascia on the lateral side of the anterior surface of the wrist and attaches to the anterior surfaces of the bases of metacarpals II and III.


Anatomy_Gray

Anatomy_Gray. The flexor carpi radialis is a powerful flexor of the wrist and can also abduct the wrist. The pronator teres muscle originates from the medial epicondyle and supraepicondylar ridge of the humerus and from a small linear region on the medial edge of the coronoid process of the ulna (Fig. 7.85A). The median nerve often exits the cubital fossa by passing between the humeral and ulnar heads of this muscle. The pronator teres crosses the forearm and attaches to an oval roughened area on the lateral surface of the radius approximately midway along the bone. The pronator teres forms the medial border of the cubital fossa and rotates the radius over the ulna during pronation (Table 7.10).


Anatomy_Gray

Anatomy_Gray. The pronator teres forms the medial border of the cubital fossa and rotates the radius over the ulna during pronation (Table 7.10). The muscle in the intermediate layer of the anterior compartment of the forearm is the flexor digitorum superficialis muscle (Fig. 7.86). This large muscle has two heads: the humero-ulnar head, which originates mainly from the medial epicondyle of the humerus and from the adjacent medial edge of the coronoid process of the ulna; and the radial head, which originates from the anterior oblique line of the radius. The median nerve and ulnar artery pass deep to the flexor digitorum superficialis between the two heads. In the distal forearm, the flexor digitorum superficialis forms four tendons, which pass through the carpal tunnel of the wrist and into the four fingers. The tendons for the ring and middle fingers are superficial to the tendons for the index and little fingers.


Anatomy_Gray

Anatomy_Gray. In the forearm, carpal tunnel, and proximal regions of the four fingers, the tendons of the flexor digitorum superficialis are anterior to the tendons of the flexor digitorum profundus muscle. Near the base of the proximal phalanx of each finger, the tendon of the flexor digitorum superficialis splits into two parts to pass posteriorly around each side of the tendon of the flexor digitorum profundus and ultimately attach to the margins of the middle phalanx (Fig. 7.86). The flexor digitorum superficialis flexes the metacarpophalangeal joint and proximal interphalangeal joint of each finger; it also flexes the wrist joint (Table 7.11). There are three deep muscles in the anterior compartment of the forearm: the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus (Fig. 7.87).


Anatomy_Gray

Anatomy_Gray. There are three deep muscles in the anterior compartment of the forearm: the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus (Fig. 7.87). The flexor digitorum profundus muscle originates from the anterior and medial surfaces of the ulna and from the adjacent half of the anterior surface of the interosseous membrane (Fig. 7.87). It gives rise to four tendons, which pass through the carpal tunnel into the four medial fingers. Throughout most of their course, the tendons are deep to the tendons of the flexor digitorum superficialis muscle. Opposite the proximal phalanx of each finger, each tendon of the flexor digitorum profundus passes through a split formed in the overlying tendon of the flexor digitorum superficialis muscle and passes distally to insert into the anterior surface of the base of the distal phalanx. In the palm, the lumbrical muscles originate from the sides of the tendons of the flexor digitorum profundus (see Fig. 7.108).


Anatomy_Gray

Anatomy_Gray. In the palm, the lumbrical muscles originate from the sides of the tendons of the flexor digitorum profundus (see Fig. 7.108). Innervation of the medial and lateral halves of the flexor digitorum profundus varies as follows: The lateral half (associated with the index and middle fingers) is innervated by the anterior interosseous nerve (branch of the median nerve). The medial half (the part associated with the ring and little fingers) is innervated by the ulnar nerve. The flexor digitorum profundus flexes the metacarpophalangeal joints and the proximal and distal interphalangeal joints of the four fingers. Because the tendons cross the wrist, it can flex the wrist joint as well (Table 7.12).


Anatomy_Gray

Anatomy_Gray. The flexor pollicis longus muscle originates from the anterior surface of the radius and the adjacent half of the anterior surface of the interosseous membrane (Fig. 7.87). It is a powerful muscle and forms a single large tendon, which passes through the carpal tunnel, lateral to the tendons of the flexor digitorum superficialis and flexor digitorum profundus muscles, and into the thumb where it attaches to the base of the distal phalanx. The flexor pollicis longus flexes the thumb and is innervated by the anterior interosseous nerve (branch of the median nerve) (Table 7.12). The pronator quadratus muscle is a flat square-shaped muscle in the distal forearm (Fig. 7.87). It originates from a linear ridge on the anterior surface of the lower end of the ulna and passes laterally to insert onto the flat anterior surface of the radius. It lies deep to, and is crossed by, the tendons of the flexor digitorum profundus and flexor pollicis longus muscles.


Anatomy_Gray

Anatomy_Gray. The pronator quadratus muscle pulls the distal end of the radius anteriorly over the ulna during pronation and is innervated by the anterior interosseous nerve (branch of the median nerve) (Table 7.12). The largest arteries in the forearm are in the anterior compartment, pass distally to supply the hand, and give rise to vessels that supply the posterior compartment (Fig. 7.88). The brachial artery enters the forearm from the arm by passing through the cubital fossa. At the apex of the cubital fossa, it divides into its two major branches, the radial and ulnar arteries.


Anatomy_Gray

Anatomy_Gray. The brachial artery enters the forearm from the arm by passing through the cubital fossa. At the apex of the cubital fossa, it divides into its two major branches, the radial and ulnar arteries. The radial artery originates from the brachial artery at approximately the neck of the radius and passes along the lateral aspect of the forearm (Fig. 7.88). It is: just deep to the brachioradialis muscle in the proximal half of the forearm, related on its lateral side to the superficial branch of the radial nerve in the middle third of the forearm, and medial to the tendon of the brachioradialis muscle and covered only by deep fascia, superficial fascia, and skin in the distal forearm.


Anatomy_Gray

Anatomy_Gray. In the distal forearm, the radial artery lies immediately lateral to the large tendon of the flexor carpi radialis muscle and directly anterior to the pronator quadratus muscle and the distal end of the radius (Fig. 7.88). In the distal forearm, the radial artery can be located using the flexor carpi radialis muscle as a landmark. The radial pulse can be felt by gently palpating the radial artery against the underlying muscle and bone. The radial artery leaves the forearm, passes around the lateral side of the wrist, and penetrates the posterolateral aspect of the hand between the bases of metacarpals I and II (Fig. 7.88). Branches of the radial artery in the hand often provide the major blood supply to the thumb and lateral side of the index finger.


Anatomy_Gray

Anatomy_Gray. Branches of the radial artery originating in the forearm include: a radial recurrent artery, which contributes to an anastomotic network around the elbow joint and to numerous vessels that supply muscles on the lateral side of the forearm (see Fig. 7.66B); a small palmar carpal branch, which contributes to an anastomotic network of vessels that supply the carpal bones and joints; a somewhat larger branch, the superficial palmar branch, which enters the hand by passing through, or superficial to, the thenar muscles at the base of the thumb (Fig. 7.88) and anastomoses with the superficial palmar arch formed by the ulnar artery. The ulnar artery is larger than the radial artery and passes down the medial side of the forearm (Fig. 7.88). It leaves the cubital fossa by passing deep to the pronator teres muscle, and then passes through the forearm in the fascial plane between the flexor carpi ulnaris and flexor digitorum profundus muscles.


Anatomy_Gray

Anatomy_Gray. In the distal forearm, the ulnar artery often remains tucked under the anterolateral lip of the flexor carpi ulnaris tendon, and is therefore not easily palpable. In distal regions of the forearm, the ulnar nerve is immediately medial to the ulnar artery. The ulnar artery leaves the forearm, enters the hand by passing lateral to the pisiform bone and superficial to the flexor retinaculum of the wrist, and arches over the palm (Fig. 7.88). It is often the major blood supply to the medial three and one-half digits.


Anatomy_Gray

Anatomy_Gray. Branches of the ulnar artery that arise in the forearm include: the ulnar recurrent artery with anterior and posterior branches, which contribute to an anastomotic network of vessels around the elbow joint (see Fig. 7.66B); numerous muscular arteries, which supply surrounding muscles; the common interosseous artery, which divides into anterior and posterior interosseous arteries (Fig. 7.88); and two small carpal arteries (dorsal carpal branch and palmar carpal branch), which supply the wrist. The posterior interosseous artery passes dorsally over the proximal margin of the interosseous membrane into the posterior compartment of the forearm.


Anatomy_Gray

Anatomy_Gray. The posterior interosseous artery passes dorsally over the proximal margin of the interosseous membrane into the posterior compartment of the forearm. The anterior interosseous artery passes distally along the anterior aspect of the interosseous membrane and supplies muscles of the deep compartment of the forearm and the radius and ulna. It has numerous branches, which perforate the interosseous membrane to supply deep muscles of the posterior compartment; it also has a small branch, which contributes to the vascular network around the carpal bones and joints. Perforating the interosseous membrane in the distal forearm, the anterior interosseous artery terminates by joining the posterior interosseous artery. Deep veins of the anterior compartment generally accompany the arteries and ultimately drain into brachial veins associated with the brachial artery in the cubital fossa.


Anatomy_Gray

Anatomy_Gray. Deep veins of the anterior compartment generally accompany the arteries and ultimately drain into brachial veins associated with the brachial artery in the cubital fossa. Nerves in the anterior compartment of the forearm are the median and ulnar nerves and the superficial branch of the radial nerve (Fig. 7.89). The median nerve innervates the muscles in the anterior compartment of the forearm except for the flexor carpi ulnaris and the medial part of the flexor digitorum profundus (ring and little fingers). It leaves the cubital fossa by passing between the two heads of the pronator teres muscle and passing between the humero-ulnar and radial heads of the flexor digitorum superficialis muscle (Fig. 7.89).


Anatomy_Gray

Anatomy_Gray. The median nerve continues a straight linear course distally down the forearm in the fascia on the deep surface of the flexor digitorum superficialis muscle. Just proximal to the wrist, it moves around the lateral side of the muscle and becomes more superficial in position, lying between the tendons of the palmaris longus and flexor carpi radialis muscles. It leaves the forearm and enters the palm of the hand by passing through the carpal tunnel deep to the flexor retinaculum. Most branches to the muscles in the superficial and intermediate layers of the forearm originate medially from the nerve just distal to the elbow joint.


Anatomy_Gray

Anatomy_Gray. Most branches to the muscles in the superficial and intermediate layers of the forearm originate medially from the nerve just distal to the elbow joint. The largest branch of the median nerve in the forearm is the anterior interosseous nerve, which originates between the two heads of the pronator teres, passes distally down the forearm with the anterior interosseous artery, innervates the muscles in the deep layer (the flexor pollicis longus, the lateral half of the flexor digitorum profundus, and the pronator quadratus) and terminates as articular branches to joints of the distal forearm and wrist. A small palmar branch originates from the median nerve in the distal forearm immediately proximal to the flexor retinaculum (Fig. 7.89), passes superficially into the hand, and innervates the skin over the base and central palm. This palmar branch is spared in carpal tunnel syndrome because it passes into the hand superficial to the flexor retinaculum of the wrist.


Anatomy_Gray

Anatomy_Gray. The ulnar nerve passes through the forearm and into the hand, where most of its major branches occur. In the forearm, the ulnar nerve innervates only the flexor carpi ulnaris muscle and the medial part (ring and little fingers) of the flexor digitorum profundus muscle (Fig. 7.89). The ulnar nerve enters the anterior compartment of the forearm by passing posteriorly around the medial epicondyle of the humerus and between the humeral and ulnar heads of the flexor carpi ulnaris muscle. After passing down the medial side of the forearm in the plane between the flexor carpi ulnaris and the flexor digitorum profundus muscles, it lies under the lateral lip of the tendon of the flexor carpi ulnaris proximal to the wrist. The ulnar artery is lateral to the ulnar nerve in the distal two-thirds of the forearm, and both the ulnar artery and nerve enter the hand by passing superficial to the flexor retinaculum and immediately lateral to the pisiform bone (Fig. 7.89).


Anatomy_Gray

Anatomy_Gray. In the forearm the ulnar nerve gives rise to: muscular branches to the flexor carpi ulnaris and to the medial half of the flexor digitorum profundus that arise soon after the ulnar nerve enters the forearm; and two small cutaneous branches—the palmar branch originates in the middle of the forearm and passes into the hand to supply skin on the medial side of the palm; the larger dorsal branch originates from the ulnar nerve in the distal forearm and passes posteriorly deep to the tendon of the flexor carpi ulnaris and innervates skin on the posteromedial side of the back of the hand and most skin on the posterior surfaces of the medial one and one-half digits. The radial nerve bifurcates into deep and superficial branches under the margin of the brachioradialis muscle in the lateral border of the cubital fossa (Fig. 7.89).


Anatomy_Gray

Anatomy_Gray. The radial nerve bifurcates into deep and superficial branches under the margin of the brachioradialis muscle in the lateral border of the cubital fossa (Fig. 7.89). The deep branch is predominantly motor and passes between the superficial and deep layers of the supinator muscle to access and supply muscles in the posterior compartment of the forearm. The superficial branch of the radial nerve is sensory. It passes down the anterolateral aspect of the forearm deep to the brachioradialis muscle and in association with the radial artery. Approximately two-thirds of the way down the forearm, the superficial branch of the radial nerve passes laterally and posteriorly around the radial side of the forearm deep to the tendon of the brachioradialis. The nerve continues into the hand where it innervates skin on the posterolateral surface.


Anatomy_Gray

Anatomy_Gray. Muscles in the posterior compartment of the forearm occur in two layers: a superficial and a deep layer. The muscles are associated with: movement of the wrist joint, extension of the fingers and thumb, and supination. All muscles in the posterior compartment of the forearm are innervated by the radial nerve. The seven muscles in the superficial layer are the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus (Fig. 7.90). All have a common origin from the supraepicondylar ridge and lateral epicondyle of the humerus and, except for the brachioradialis and anconeus, extend as tendons into the hand. The brachioradialis muscle originates from the proximal part of the supraepicondylar ridge of the humerus and passes through the forearm to insert on the lateral side of the distal end of the radius just proximal to the radial styloid process (Fig. 7.90).


Anatomy_Gray

Anatomy_Gray. In the anatomical position, the brachioradialis is part of the muscle mass overlying the anterolateral surface of the forearm and forms the lateral boundary of the cubital fossa. Because the brachioradialis is anterior to the elbow joint, it acts as an accessory flexor of this joint even though it is in the posterior compartment of the forearm. Its action is most efficient when the forearm is midpronated and it forms a prominent bulge as it acts against resistance. The radial nerve emerges from the posterior compartment of the arm just deep to the brachioradialis in the distal arm and innervates the brachioradialis. Lateral to the cubital fossa, the brachioradialis lies over the radial nerve and its bifurcation into deep and superficial branches. In more distal regions, the brachioradialis lies over the superficial branch of the radial nerve and radial artery (Table 7.13).


Anatomy_Gray

Anatomy_Gray. The extensor carpi radialis longus muscle originates from the distal part of the supraepicondylar ridge and the lateral epicondyle of the humerus; its tendon inserts on the dorsal surface of the base of metacarpal II (Fig. 7.90). In proximal regions, it is deep to the brachioradialis muscle. The extensor carpi radialis longus muscle extends and abducts the wrist, and is innervated by the radial nerve before the nerve divides into superficial and deep branches (Table 7.13). The extensor carpi radialis brevis muscle originates from the lateral epicondyle of the humerus, and the tendon inserts onto adjacent dorsal surfaces of the bases of metacarpals II and III (Fig. 7.90). Along much of its course, the extensor carpi radialis brevis lies deep to the extensor carpi radialis longus.


Anatomy_Gray

Anatomy_Gray. The extensor carpi radialis brevis muscle extends and abducts the wrist, and is innervated by the deep branch of the radial nerve before the nerve passes between the two heads of the supinator muscle (Table 7.13). The extensor digitorum muscle is the major extensor of the four fingers (index, middle, ring, and little fingers). It originates from the lateral epicondyle of the humerus and forms four tendons, each of which passes into a finger (Fig. 7.90). On the dorsal surface of the hand, adjacent tendons of the extensor digitorum are interconnected. In the fingers, each tendon inserts, via a triangular-shaped connective tissue aponeurosis (the extensor hood), into the base of the dorsal surfaces of the middle and distal phalanges. The extensor digitorum muscle is innervated by the posterior interosseous nerve, which is the continuation of the deep branch of the radial nerve after it emerges from the supinator muscle (Table 7.13).


Anatomy_Gray

Anatomy_Gray. The extensor digiti minimi muscle is an accessory extensor of the little finger and is medial to the extensor digitorum in the forearm (Fig. 7.90). It originates from the lateral epicondyle of the humerus and inserts, together with the tendon of the extensor digitorum, into the extensor hood of the little finger. The extensor digiti minimi is innervated by the posterior interosseous nerve (Table 7.13). The extensor carpi ulnaris muscle is medial to the extensor digiti minimi (Fig. 7.90). It originates from the lateral epicondyle, and its tendon inserts into the medial side of the base of metacarpal V. The extensor carpi ulnaris extends and adducts the wrist, and is innervated by the posterior interosseous nerve (Table 7.13).


Anatomy_Gray

Anatomy_Gray. The extensor carpi ulnaris extends and adducts the wrist, and is innervated by the posterior interosseous nerve (Table 7.13). The anconeus muscle is the most medial of the superficial extensors and has a triangular shape. It originates from the lateral epicondyle of the humerus and has a broad insertion into the posterolateral surface of the olecranon and related posterior surface of the ulna (see Fig. 7.84). The anconeus abducts the ulna during pronation to maintain the center of the palm over the same point when the hand is flipped. It is also considered to be an accessory extensor of the elbow joint. The anconeus is innervated by the branch of the radial nerve that innervates the medial head of the triceps brachii muscle (Table 7.13). The deep layer of the posterior compartment of the forearm consists of five muscles: supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis (Fig. 7.91).


Anatomy_Gray

Anatomy_Gray. Except for the supinator muscle, all these deep layer muscles originate from the posterior surfaces of the radius, ulna, and interosseous membrane and pass into the thumb and fingers. Three of these muscles—the abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus—emerge from between the extensor digitorum and the extensor carpi radialis brevis tendons of the superficial layer and pass into the thumb. Two of the three “outcropping” muscles (the abductor pollicis longus and extensor pollicis brevis) form a distinct muscular bulge in the distal posterolateral surface of the forearm. All muscles of the deep layer are innervated by the posterior interosseous nerve, the continuation of the deep branch of the radial nerve. The supinator muscle has two layers, which insert together on the proximal aspect of the radius (Fig. 7.91):


Anatomy_Gray

Anatomy_Gray. The supinator muscle has two layers, which insert together on the proximal aspect of the radius (Fig. 7.91): The more superficial (humeral) layer originates mainly from the lateral epicondyle of the humerus and the related anular ligament and the radial collateral ligament of the elbow joint. The deep (ulnar) layer originates mainly from the supinator crest on the posterolateral surface of the ulna. From their sites of origin, the two layers wrap around the posterior and lateral aspect of the head, neck, and proximal shaft of the radius to insert on the lateral surface of the radius superior to the anterior oblique line and to the insertion of the pronator teres muscle. The supinator muscle supinates the forearm and hand. The deep branch of the radial nerve innervates the supinator muscle and passes to the posterior compartment of the forearm by passing between the two heads of this muscle (Table 7.14).


Anatomy_Gray

Anatomy_Gray. The deep branch of the radial nerve innervates the supinator muscle and passes to the posterior compartment of the forearm by passing between the two heads of this muscle (Table 7.14). The abductor pollicis longus muscle originates from the proximal posterior surfaces of the radius and the ulna and from the related interosseous membrane (Fig. 7.91). In the distal forearm, it emerges between the extensor digitorum and extensor carpi radialis brevis muscles to form a tendon that passes into the thumb and inserts on the lateral side of the base of metacarpal I. The tendon contributes to the lateral border of the anatomical snuffbox at the wrist. The major function of the abductor pollicis longus is to abduct the thumb at the joint between the metacarpal I and trapezium bones (Table 7.14).


Anatomy_Gray

Anatomy_Gray. The major function of the abductor pollicis longus is to abduct the thumb at the joint between the metacarpal I and trapezium bones (Table 7.14). The extensor pollicis brevis muscle arises distal to the origin of the abductor pollicis longus from the posterior surface of the radius and interosseous membrane (Fig. 7.91). Together with the abductor pollicis longus, it emerges between the extensor digitorum and extensor carpi radialis brevis muscles to form a bulge on the posterolateral surface of the distal forearm. The tendon of the extensor pollicis brevis passes into the thumb and inserts on the dorsal surface of the base of the proximal phalanx. At the wrist, the tendon contributes to the lateral border of the anatomical snuffbox. The extensor pollicis brevis extends the metacarpophalangeal and carpometacarpal joints of the thumb (Table 7.14).


Anatomy_Gray

Anatomy_Gray. The extensor pollicis brevis extends the metacarpophalangeal and carpometacarpal joints of the thumb (Table 7.14). The extensor pollicis longus muscle originates from the posterior surface of the ulna and adjacent interosseous membrane and inserts via a long tendon into the dorsal surface of the distal phalanx of the thumb (Fig. 7.91). Like the abductor pollicis longus and extensor pollicis brevis, the tendon of this muscle emerges between the extensor digitorum and the extensor carpi radialis brevis muscles. However, it is held away from the other two deep muscles of the thumb by passing medially around the dorsal tubercle on the distal end of the radius. The tendon forms the medial margin of the anatomical snuffbox at the wrist. The extensor pollicis longus extends all joints of the thumb (Table 7.14).


Anatomy_Gray

Anatomy_Gray. The extensor pollicis longus extends all joints of the thumb (Table 7.14). The extensor indicis muscle is an accessory extensor of the index finger. It originates distal to the extensor pollicis longus from the posterior surface of the ulna and adjacent interosseous membrane (Fig. 7.91). The tendon passes into the hand and inserts into the extensor hood of the index finger with the tendon of the extensor digitorum (Table 7.14). The blood supply to the posterior compartment of the forearm occurs predominantly through branches of the radial, posterior interosseous, and anterior interosseous arteries (Fig. 7.92).


Anatomy_Gray

Anatomy_Gray. The blood supply to the posterior compartment of the forearm occurs predominantly through branches of the radial, posterior interosseous, and anterior interosseous arteries (Fig. 7.92). The posterior interosseous artery originates in the anterior compartment from the common interosseous branch of the ulnar artery and passes posteriorly over the proximal margin of the interosseous membrane and into the posterior compartment of the forearm. It contributes a branch, the recurrent interosseous artery (see Fig. 7.66B), to the vascular network around the elbow joint and then passes between the supinator and abductor pollicis longus muscles to supply the superficial extensors. After receiving the terminal end of the anterior interosseous artery, the posterior interosseous artery terminates by joining the dorsal carpal arch of the wrist.


Anatomy_Gray

Anatomy_Gray. The anterior interosseous artery, also a branch of the common interosseous branch of the ulnar artery, is situated in the anterior compartment of the forearm on the interosseous membrane. It has numerous perforating branches, which pass directly through the interosseous membrane to supply deep muscles of the posterior compartment. The terminal end of the anterior interosseous artery passes posteriorly through an aperture in the interosseous membrane in distal regions of the forearm to join the posterior interosseous artery. The radial artery has muscular branches, which contribute to the supply of the extensor muscles on the radial side of the forearm. Deep veins of the posterior compartment generally accompany the arteries. They ultimately drain into brachial veins associated with the brachial artery in the cubital fossa.


Anatomy_Gray

Anatomy_Gray. Deep veins of the posterior compartment generally accompany the arteries. They ultimately drain into brachial veins associated with the brachial artery in the cubital fossa. The nerve of the posterior compartment of the forearm is the radial nerve (Fig. 7.92). Most of the muscles are innervated by the deep branch, which originates from the radial nerve in the lateral wall of the cubital fossa deep to the brachioradialis muscle and becomes the posterior interosseous nerve after emerging from between the superficial and deep layers of the supinator muscle in the posterior compartment of the forearm. In the lateral wall of the cubital fossa, and before dividing into superficial and deep branches, the radial nerve innervates the brachioradialis and extensor carpi radialis longus muscles.


Anatomy_Gray

Anatomy_Gray. In the lateral wall of the cubital fossa, and before dividing into superficial and deep branches, the radial nerve innervates the brachioradialis and extensor carpi radialis longus muscles. The deep branch innervates the extensor carpi radialis brevis, then passes between the two layers of the supinator muscle and follows the plane of separation between the two layers dorsally and laterally around the proximal shaft of the radius to the posterior aspect of the forearm. It supplies the supinator muscle and then emerges, as the posterior interosseous nerve, from the muscle to lie between the superficial and deep layers of muscles. The posterior interosseous nerve supplies the remaining muscles in the posterior compartment and terminates as articular branches, which pass deep to the extensor pollicis longus muscle to reach the wrist.


Anatomy_Gray

Anatomy_Gray. The hand (Fig. 7.93) is the region of the upper limb distal to the wrist joint. It is subdivided into three parts: the wrist (carpus), the metacarpus, and the digits (five fingers including the thumb). The five digits consist of the laterally positioned thumb and, medial to the thumb, the four fingers—the index, middle, ring, and little fingers. In the normal resting position, the fingers form a flexed arcade, with the little finger flexed most and the index finger flexed least. In the anatomical position, the fingers are extended. The hand has an anterior surface (palm) and a dorsal surface (dorsum of hand). Abduction and adduction of the fingers are defined with respect to the long axis of the middle finger (Fig. 7.93). In the anatomical position, the long axis of the thumb is rotated 90° to the rest of the digits so that the pad of the thumb points medially; consequently, movements of the thumb are defined at right angles to the movements of the other digits of the hand.


Anatomy_Gray

Anatomy_Gray. The hand is a mechanical and sensory tool. Many of the features of the upper limb are designed to facilitate positioning the hand in space. There are three groups of bones in the hand: The eight carpal bones are the bones of the wrist. The five metacarpals (I to V) are the bones of the metacarpus. The phalanges are the bones of the digits—the thumb has only two; the rest of the digits have three (Fig. 7.94). The carpal bones and metacarpals of the index, middle, ring, and little fingers (metacarpals II to V) tend to function as a unit and form much of the bony framework of the palm. The metacarpal of the thumb functions independently and has increased flexibility at the carpometacarpal joint to provide opposition of the thumb to the fingers. The small carpal bones of the wrist are arranged in two rows, a proximal and a distal row, each consisting of four bones (Fig. 7.94).


Anatomy_Gray

Anatomy_Gray. The small carpal bones of the wrist are arranged in two rows, a proximal and a distal row, each consisting of four bones (Fig. 7.94). From lateral to medial and when viewed from anteriorly, the proximal row of bones consists of: the boat-shaped scaphoid, the lunate, which has a crescent shape, the three-sided triquetrum bone, and the pea-shaped pisiform (Fig. 7.94). The pisiform is a sesamoid bone in the tendon of the flexor carpi ulnaris and articulates with the anterior surface of the triquetrum. The scaphoid has a prominent tubercle on its lateral palmar surface that is directed anteriorly. From lateral to medial and when viewed from anteriorly, the distal row of carpal bones consists of: the irregular four-sided trapezium bone, the four-sided trapezoid, the capitate, which has a head, and the hamate, which has a hook (Fig. 7.94). The trapezium articulates with the metacarpal bone of the thumb and has a distinct tubercle on its palmar surface that projects anteriorly.


Anatomy_Gray

Anatomy_Gray. The trapezium articulates with the metacarpal bone of the thumb and has a distinct tubercle on its palmar surface that projects anteriorly. The largest of the carpal bones, the capitate, articulates with the base of metacarpal III. The hamate, which is positioned just lateral and distal to the pisiform, has a prominent hook (hook of hamate) on its palmar surface that projects anteriorly. The carpal bones have numerous articular surfaces (Fig. 7.94). All of them articulate with each other, and the carpal bones in the distal row articulate with the metacarpals of the digits. With the exception of the metacarpal of the thumb, all movements of the metacarpal bones on the carpal bones are limited. The expansive proximal surfaces of the scaphoid and lunate articulate with the radius to form the wrist joint.


Anatomy_Gray

Anatomy_Gray. The expansive proximal surfaces of the scaphoid and lunate articulate with the radius to form the wrist joint. The carpal bones do not lie in a flat plane; rather, they form an arch, whose base is directed anteriorly (Fig. 7.94). The lateral side of this base is formed by the tubercles of the scaphoid and trapezium. The medial side is formed by the pisiform and the hook of the hamate. The flexor retinaculum attaches to, and spans the distance between, the medial and lateral sides of the base to form the anterior wall of the so-called carpal tunnel. The sides and roof of the carpal tunnel are formed by the arch of the carpal bones. Each of the five metacarpals is related to one digit: Metacarpal I is related to the thumb. Metacarpals II to V are related to the index, middle, ring, and little fingers, respectively (Fig. 7.94). Each metacarpal consists of a base, a shaft (body), and distally, a head.


Anatomy_Gray

Anatomy_Gray. Metacarpals II to V are related to the index, middle, ring, and little fingers, respectively (Fig. 7.94). Each metacarpal consists of a base, a shaft (body), and distally, a head. All of the bases of the metacarpals articulate with the carpal bones; in addition, the bases of the metacarpal bones of the fingers articulate with each other. All of the heads of the metacarpals articulate with the proximal phalanges of the digits. The heads form the knuckles on the dorsal surface of the hand when the fingers are flexed. The phalanges are the bones of the digits (Fig. 7.94): The thumb has two—a proximal and a distal phalanx. The rest of the digits have three—a proximal, a middle, and a distal phalanx. Each phalanx has a base, a shaft (body), and distally, a head. The base of each proximal phalanx articulates with the head of the related metacarpal bone.


Anatomy_Gray

Anatomy_Gray. Each phalanx has a base, a shaft (body), and distally, a head. The base of each proximal phalanx articulates with the head of the related metacarpal bone. The head of each distal phalanx is nonarticular and flattened into a crescent-shaped palmar tuberosity, which lies under the palmar pad at the end of the digit. The wrist joint is a synovial joint between the distal end of the radius and the articular disc overlying the distal end of the ulna, and the scaphoid, lunate, and triquetrum (Fig. 7.94). Together, the articular surfaces of the carpals form an oval shape with a convex contour, which articulates with the corresponding concave surface of the radius and articular disc. The wrist joint allows movement around two axes. The hand can be abducted, adducted, flexed, and extended at the wrist joint. Because the radial styloid process extends further distally than does the ulnar styloid process, the hand can be adducted to a greater degree than it can be abducted.


Anatomy_Gray

Anatomy_Gray. Because the radial styloid process extends further distally than does the ulnar styloid process, the hand can be adducted to a greater degree than it can be abducted. The capsule of the wrist joint is reinforced by palmar radiocarpal, palmar ulnocarpal, and dorsal radiocarpal ligaments. In addition, radial and ulnar collateral ligaments of the wrist joint span the distance between the styloid processes of the radius and ulna and the adjacent carpal bones. These ligaments reinforce the medial and lateral sides of the wrist joint and support them during flexion and extension. The synovial joints between the carpal bones share a common articular cavity. The joint capsule of the joints is reinforced by numerous ligaments. Although movement at the carpal joints (intercarpal joints) is limited, the joints do contribute to the positioning of the hand in abduction, adduction, flexion, and, particularly, extension.


Anatomy_Gray

Anatomy_Gray. Although movement at the carpal joints (intercarpal joints) is limited, the joints do contribute to the positioning of the hand in abduction, adduction, flexion, and, particularly, extension. There are five carpometacarpal joints between the metacarpals and the related distal row of carpal bones (Fig. 7.94). The saddle joint, between metacarpal I and the trapezium, imparts a wide range of mobility to the thumb that is not a feature of the rest of the digits. Movements at this carpometacarpal joint are flexion, extension, abduction, adduction, rotation, and circumduction. The carpometacarpal joints between metacarpals II to V and the carpal bones are much less mobile than the carpometacarpal joint of the thumb, allowing only limited gliding movements. Movement of the joints increases medially, so metacarpal V slides to the greatest degree. This can be best observed on the dorsal surface of the hand as it makes a fist.


Anatomy_Gray

Anatomy_Gray. The joints between the distal heads of the metacarpals and the proximal phalanges of the digits are condylar joints, which allow flexion, extension, abduction, adduction, circumduction, and limited rotation (Fig. 7.94). The capsule of each joint is reinforced by the palmar ligament and by medial and lateral collateral ligaments. The three deep transverse metacarpal ligaments (Fig. 7.95) are thick bands of connective tissue connecting the palmar ligaments of the metacarpophalangeal joints of the fingers to each other. They are important because, by linking the heads of the metacarpal bones together, they restrict the movement of these bones relative to each other. As a result, they help form a unified skeletal framework for the palm of the hand.


Anatomy_Gray

Anatomy_Gray. Significantly, a deep transverse metacarpal ligament does not occur between the palmar ligament of the metacarpophalangeal joint of the thumb and the palmar ligament of the index finger. The absence of this ligament, and the presence of a saddle joint between metacarpal I and the trapezium, are responsible for the increased mobility of the thumb relative to the rest of the digits of the hand. Interphalangeal joints of hand The interphalangeal joints of the hand are hinge joints that allow mainly flexion and extension. They are reinforced by medial and lateral collateral ligaments and palmar ligaments. Carpal tunnel and structures at the wrist The carpal tunnel is formed anteriorly at the wrist by a deep arch formed by the carpal bones and the flexor retinaculum (see Fig. 7.94). The base of the carpal arch is formed medially by the pisiform and the hook of the hamate and laterally by the tubercles of the scaphoid and trapezium.


Anatomy_Gray

Anatomy_Gray. The base of the carpal arch is formed medially by the pisiform and the hook of the hamate and laterally by the tubercles of the scaphoid and trapezium. The flexor retinaculum is a thick connective tissue ligament that bridges the space between the medial and lateral sides of the base of the arch and converts the carpal arch into the carpal tunnel. The four tendons of the flexor digitorum profundus, the four tendons of the flexor digitorum superficialis, and the tendon of the flexor pollicis longus pass through the carpal tunnel, as does the median nerve (Fig. 7.98). The flexor retinaculum holds the tendons to the bony plane at the wrist and prevents them from “bowing.”


Anatomy_Gray

Anatomy_Gray. The flexor retinaculum holds the tendons to the bony plane at the wrist and prevents them from “bowing.” Free movement of the tendons in the carpal tunnel is facilitated by synovial sheaths, which surround the tendons. All the tendons of the flexor digitorum profundus and flexor digitorum superficialis are surrounded by a single synovial sheath; a separate sheath surrounds the tendon of the flexor pollicis longus. The median nerve is anterior to the tendons in the carpal tunnel. The tendon of the flexor carpi radialis is surrounded by a synovial sheath and passes through a tubular compartment formed by the attachment of the lateral aspect of the flexor retinaculum to the margins of a groove on the medial side of the tubercle of the trapezium.


Anatomy_Gray

Anatomy_Gray. The ulnar artery, ulnar nerve, and tendon of the palmaris longus pass into the hand anterior to the flexor retinaculum and therefore do not pass through the carpal tunnel (Fig. 7.98). The tendon of the palmaris longus is not surrounded by a synovial sheath. The radial artery passes dorsally around the lateral side of the wrist and lies adjacent to the external surface of the scaphoid. The extensor tendons pass into the hand on the medial, lateral, and posterior surfaces of the wrist in six compartments defined by an extensor retinaculum and lined by synovial sheaths (Fig. 7.98): The tendons of the extensor digitorum and extensor indicis share a compartment and synovial sheath on the posterior surface of the wrist. The tendons of the extensor carpi ulnaris and extensor digiti minimi have separate compartments and sheaths on the medial side of the wrist.


Anatomy_Gray

Anatomy_Gray. The tendons of the extensor carpi ulnaris and extensor digiti minimi have separate compartments and sheaths on the medial side of the wrist. The tendons of the abductor pollicis longus and extensor pollicis brevis muscles, the extensor carpi radialis longus and extensor carpi radialis brevis muscles, and the extensor pollicis longus muscle pass through three compartments on the lateral surface of the wrist. The palmar aponeurosis is a triangular condensation of deep fascia that covers the palm and is anchored to the skin in distal regions (Fig. 7.99). The apex of the triangle is continuous with the palmaris longus tendon, when present; otherwise, it is anchored to the flexor retinaculum. From this point, fibers radiate to extensions at the bases of the digits that project into each of the index, middle, ring, and little fingers and, to a lesser extent, the thumb. Transverse fibers interconnect the more longitudinally arranged bundles that continue into the digits.


Anatomy_Gray

Anatomy_Gray. Transverse fibers interconnect the more longitudinally arranged bundles that continue into the digits. Vessels, nerves, and long flexor tendons lie deep to the palmar aponeurosis in the palm. The palmaris brevis, a small intrinsic muscle of the hand, is a quadrangular-shaped subcutaneous muscle that overlies the hypothenar muscles, ulnar artery, and superficial branch of the ulnar nerve at the medial side of the palm (Fig. 7.99). It originates from the palmar aponeurosis and flexor retinaculum and inserts into the dermis of the skin on the medial margin of the hand. The palmaris brevis deepens the cup of the palm by pulling on skin over the hypothenar eminence and forming a distinct ridge. This may improve grip. The palmaris brevis is innervated by the superficial branch of the ulnar nerve.


Anatomy_Gray

Anatomy_Gray. The palmaris brevis is innervated by the superficial branch of the ulnar nerve. The “anatomical snuffbox” is a term given to the triangular depression formed on the posterolateral side of the wrist and metacarpal I by the extensor tendons passing into the thumb (Fig. 7.100). Historically, ground tobacco (snuff) was placed in this depression before being inhaled into the nose. The base of the triangle is at the wrist and the apex is directed into the thumb. The impression is most apparent when the thumb is extended: The lateral border is formed by the tendons of the abductor pollicis longus and extensor pollicis brevis. The medial border is formed by the tendon of the extensor pollicis longus. The floor of the impression is formed by the scaphoid and trapezium, and the distal ends of the tendons of the extensor carpi radialis longus and extensor carpi radialis brevis.


Anatomy_Gray

Anatomy_Gray. The floor of the impression is formed by the scaphoid and trapezium, and the distal ends of the tendons of the extensor carpi radialis longus and extensor carpi radialis brevis. The radial artery passes obliquely through the anatomical snuffbox, deep to the extensor tendons of the thumb and lies adjacent to the scaphoid and trapezium. Terminal parts of the superficial branch of the radial nerve pass subcutaneously over the snuffbox as does the origin of the cephalic vein from the dorsal venous arch of the hand.


Anatomy_Gray

Anatomy_Gray. Terminal parts of the superficial branch of the radial nerve pass subcutaneously over the snuffbox as does the origin of the cephalic vein from the dorsal venous arch of the hand. After exiting the carpal tunnel, the tendons of the flexor digitorum superficialis and profundus muscles cross the palm and enter fibrous sheaths on the palmar aspect of the digits (Fig. 7.101). These fibrous sheaths: begin proximally, anterior to the metacarpophalangeal joints, and extend to the distal phalanges; are formed by fibrous arches and cruciate (cross-shaped) ligaments, which are attached posteriorly to the margins of the phalanges and to the palmar ligaments associated with the metacarpophalangeal and interphalangeal joints; and hold the tendons to the bony plane and prevent the tendons from bowing when the digits are flexed.


Anatomy_Gray

Anatomy_Gray. Within each tunnel, the tendons are surrounded by a synovial sheath. The synovial sheaths of the thumb and little finger are continuous with the sheaths associated with the tendons in the carpal tunnel (Fig. 7.101). The tendons of the extensor digitorum and extensor pollicis longus muscles pass onto the dorsal aspect of the digits and expand over the proximal phalanges to form complex “extensor hoods” or “dorsal digital expansions” (Fig. 7.103A). The tendons of the extensor digiti minimi, extensor indicis, and extensor pollicis brevis muscles join these hoods.


Anatomy_Gray

Anatomy_Gray. Each extensor hood is triangular, with: the apex attached to the distal phalanx, the central region attached to the middle phalanx (index, middle, ring, and little fingers) or proximal phalanx (thumb), and each corner of the base wrapped around the sides of the metacarpophalangeal joint—in the index, middle, ring, and little fingers, the corners of the hoods attach mainly to the deep transverse metacarpal ligaments; in the thumb, the hood is attached on each side to muscles. In addition to other attachments, many of the intrinsic muscles of the hand insert into the free margin of the hood on each side. By inserting into the extensor hood, these intrinsic muscles are responsible for complex delicate movements of the digits that could not be accomplished with the long flexor and extensor tendons alone.


Anatomy_Gray

Anatomy_Gray. In the index, middle, ring, and little fingers, the lumbrical, interossei, and abductor digiti minimi muscles attach to the extensor hoods. In the thumb, the adductor pollicis and abductor pollicis brevis muscles insert into and anchor the extensor hood. Because force from the small intrinsic muscles of the hand is applied to the extensor hood distal to the fulcrum of the metacarpophalangeal joints, the muscles flex these joints (Fig. 7.103B). Simultaneously, the force is transferred dorsally through the hood to extend the interphalangeal joints. This ability to flex the metacarpophalangeal joints, while at the same time extending the interphalangeal joints, is entirely due to the intrinsic muscles of the hand working through the extensor hoods. This type of precision movement is used in the upstroke when writing a t (Fig. 7.103C).


Anatomy_Gray

Anatomy_Gray. The intrinsic muscles of the hand are the palmaris brevis (described on p. 791; see Fig. 7.99), interossei, adductor pollicis, thenar, hypothenar, and lumbrical muscles (Figs. 7.104 to 7.108). Unlike the extrinsic muscles that originate in the forearm, insert in the hand, and function in forcefully gripping (“power grip”) with the hand, the intrinsic muscles occur entirely in the hand and mainly execute precision movements (“precision grip”) with the fingers and thumb. All of the intrinsic muscles of the hand are innervated by the deep branch of the ulnar nerve except for the three thenar and two lateral lumbrical muscles, which are innervated by the median nerve. The intrinsic muscles are predominantly innervated by spinal cord segment T1 with a contribution from C8.


Anatomy_Gray

Anatomy_Gray. The interossei are muscles between and attached to the metacarpals (Figs. 7.104 and 7.105). They insert into the proximal phalanx of each digit and into the extensor hood and are divided into two groups, the dorsal interossei and the palmar interossei. All of the interossei are innervated by the deep branch of the ulnar nerve. Collectively, the interossei abduct and adduct the digits and contribute to the complex flexion and extension movements generated by the extensor hoods. Dorsal interossei are the most dorsally situated of all of the intrinsic muscles and can be palpated through the skin on the dorsal aspect of the hand (Fig. 7.104). There are four bipennate dorsal interosseous muscles between, and attached to, the shafts of adjacent metacarpal bones (Fig. 7.104). Each muscle inserts both into the base of the proximal phalanx and into the extensor hood of its related digit. The tendons of the dorsal interossei pass dorsal to the deep transverse metacarpal ligaments:


Anatomy_Gray

Anatomy_Gray. The tendons of the dorsal interossei pass dorsal to the deep transverse metacarpal ligaments: The first dorsal interosseous muscle is the largest and inserts into the lateral side of the index finger. The second and third dorsal interossei insert into the lateral and medial sides, respectively, of the middle finger. The fourth dorsal interosseous muscle inserts into the medial side of the ring finger. In addition to generating flexion and extension movements of the fingers through their attachments to the extensor hoods, the dorsal interossei are the major abductors of the index, middle, and ring fingers, at the metacarpophalangeal joints (Table 7.15). The middle finger can abduct medially and laterally with respect to the long axis of the middle finger and consequently has a dorsal interosseous muscle on each side. The thumb and little finger have their own abductors in the thenar and hypothenar muscle groups, respectively, and therefore do not have dorsal interossei.


Anatomy_Gray

Anatomy_Gray. The radial artery passes between the two heads of the first dorsal interosseous muscle as it passes from the anatomical snuffbox on the posterolateral side of the wrist into the deep aspect of the palm. The three (or four) palmar interossei are anterior to the dorsal interossei, and are unipennate muscles originating from the metacarpals of the digits with which each is associated (Fig. 7.105). The first palmar interosseous muscle is rudimentary and often considered part of either the adductor pollicis or the flexor pollicis brevis. When present, it originates from the medial side of the palmar surface of metacarpal I and inserts into both the base of the proximal phalanx of the thumb and into the extensor hood. A sesamoid bone often occurs in the tendon attached to the base of the phalanx. The second palmar interosseous muscle originates from the medial surface of metacarpal II and inserts into the medial side of the extensor hood of the index finger.