Volume 1, BD Chaurasia Human Anatomy, Upper Limb and Thorax PDF

8 Arm  The man who gets angry, at the right things, with the right people, in the right...

8 Arm  The man who gets angry, at the right things, with the right people, in the right way, at the right time and for the right length of time is commended —Aristotle INTRODUCTION The arm extends from the shoulder joint till the elbow joint. The skeleton of the arm is a ‘solo’ bone, the humerus. Medial and lateral intermuscular septa divide the arm into an anterior or flexor compartment and a posterior or extensor compartment, to give each compartment its individuality and freedom of action. Since the structures in the front of arm continue across the elbow joint into the cubital fossa, the cubital fossa is also included in this chapter. The arm is called brachium, so most of the structures in this chapter are named accordingly, like brachialis, coracobrachialis and brachial artery. SURFACE LANDMARKS The following landmarks can be felt in the living subject. 1 The greater tubercle of the humerus is the most lateral bony point in the shoulder region. It can be felt just Fig. 8.1: Surface landmarks—front of upper arm below the acromion process, deep to the deltoid when the arm is by the side of the trunk (Fig. 8.1). the lower one-fourth of the arm as upward 2 The shaft of the humerus is felt only indistinctly continuations of the epicondyles. because it is surrounded by muscles in its upper 6 The deltoid forms the rounded contour of the half. In the lower half, the humerus is covered shoulder. The apex of the muscle is attached to the anteriorly by the biceps brachii and brachialis, and deltoid tuberosity located at the middle of the posteriorly by the triceps brachii. anterolateral surface of the humerus. 3 The medial epicondyle of the humerus is a prominent 7 The coracobrachialis forms an inconspicuous rounded bony projection on the medial side of the elbow. It ridge in the upper part of the medial side of the arm. is best seen and felt in a mid-flexed elbow. Pulsations of the brachial artery can be felt in the 4 The lateral epicondyle of the humerus is less prominent depression behind it. than the medial. It can be felt in the upper part of 8 The biceps brachii muscle is overlapped above by the the depression on the posterolateral aspect of the pectoralis major and by the deltoid. Below these elbow in the extended position of the forearm. muscles, the biceps forms a conspicuous elevation 5 The medial and lateral supracondylar ridges are better on the front of the arm. Upon flexing the elbow, the defined in the lower portions of the medial and contracting muscle becomes still more prominent. lateral borders of the humerus. They can be felt in The tendon of the biceps can be felt in front of the 94  ARM 95 elbow. The tendon is a guide to the brachial artery Two additional septa are present in the anterior which lies on its medial side. compartment of the arm. The transverse septum 9 The brachial artery can be felt in front of the elbow separates the biceps from the brachialis and encloses joint just medial to the tendon of the biceps brachii. the musculocutaneous nerve. The anteroposterior septum Brachial pulsations are used for recording the blood separates the brachialis from the muscles attached to pressure. the lateral supracondylar ridge; it encloses the radial 10 The ulnar nerve can be rolled by the palpating finger nerve and the anterior descending branch of the behind the medial epicondyle of the humerus. During profunda brachii artery. leprosy, this nerve becomes thick and enlarged. 11 The superficial cubital veins can be made more Competency achievement: The student should be able to: prominent by applying tight pressure round the arm AN 11.1 Describe and demonstrate muscle groups of upper arm and then contracting the forearm muscles by with emphasis on biceps and triceps brachii.1 clenching and releasing the fist a few times. The cephalic vein runs upwards along the lateral border of the biceps. The basilic vein can be seen along the ANTERIOR COMPARTMENT lower half of the medial border of the biceps. The cephalic and basilic veins are connected together in MUSCLES front of the elbow by the median cubital vein which Muscles of the anterior compartment of the arm are runs obliquely upwards and medially. the coracobrachialis, the biceps brachii and the brachialis. They are described in Tables 8.1 and 8.2. COMPARTMENTS OF THE ARM Morphological Importance of Coracobrachialis The arm is divided into anterior and posterior Morphologically, the muscle is very important for compartments by extension of deep fascia which are following reasons. called the medial and lateral intermuscular septa The coracobrachialis represents the medial compart- (Fig. 8.2). These septa provide additional surface for the ment, which is so well developed in the thigh. attachment of muscles. They also form planes along In some animals, it is a tricipital muscle. In human, which nerves and blood vessels travel. The septa are well the upper two heads have fused and musculocutaneous nerve passes between the two, and the lowest third head defined only in the lower half of the arm and are attached has disappeared. Persistence of the lower head in to the medial and lateral borders and supracondylar human is associated with the presence of ‘ligament of ridges of the humerus. The medial septum is pierced by Struthers’, which is a fibrous band extending from the the ulnar nerve and the superior ulnar collateral artery; trochlear spine to the medial epicondyle of the humerus, the lateral septum is pierced by the radial nerve and to which the third head of the coracobrachialis is radial collateral artery or the anterior descending branch inserted, and from the lower part of which the pronator of the profunda brachii artery (Fig. 8.7). teres muscle takes origin. Beneath the ligament pass the median nerve or brachial artery or both. The front or anterior compartment of the arm is homologous with flexor and medial compartments of the thigh. The flexor compartment of thigh lies Upper Limb posteriorly because the lower limb bud rotates medially. Competency achievement: The student should be able to: AN 11.2 Identify and describe origin, course, relations, branches (or tributaries), termination of important nerves and vessels in arm.2 NERVES Musculocutaneous Nerve 1 The musculocutaneous nerve is the main nerve of the Section front of the arm, and continues below the elbow as the lateral cutaneous nerve of the forearm (see Fig. 7.1a). It is a branch of the lateral cord of the brachial plexus, Fig. 8.2: Transverse section through the distal one-third of the arising at the lower border of the pectoralis minor (see arm, showing the intermuscular septa and the compartments Fig. 4.14) in the axilla.  UPPER LIMB 96 Table 8.1: Attachments of muscles Muscle Origin Insertion 1. Coracobrachialis The medial aspect of tip of the coracoid process with The middle 5 cm of the medial border of (see Fig. 2.8) the short head of the biceps brachii (Fig. 8.3a) the humerus 2. Biceps brachii It has two heads of origin: Posterior rough part of the radial tuberosity. (Fig. 8.3b) The short head arises with coracobrachialis from the The tendon is twisted; the anterior fibres lateral aspect of tip of the coracoid process become lateral and posterior fibres become The long head arises from the supraglenoid tubercle medial. The tendon is separated from the of the scapula and from the glenoidal labrum. The anterior part of the tuberosity by a bursa tendon is intracapsular (Fig. 8.4) The tendon gives off an extension called the bicipital aponeurosis which extends to ulna and it separates median cubital vein from brachial artery 3. Brachialis Lower half of the front of the humerus, including both Coronoid process and ulnar tuberosity (Fig. 8.5) the anteromedial and anterolateral surfaces and the Rough anterior surface of the coronoid anterior border process of the ulna Superiorly the origin embraces the insertion of the deltoid Medial and lateral intermuscular septa Table 8.2: Nerve supply and actions of muscles Muscle Nerve supply Actions 1. Coracobrachialis Musculocutaneous nerve (C5–C7) Flexes the arm at the shoulder joint (Fig. 8.3a) 2. Biceps brachii Musculocutaneous nerve (C5–C6) It is strong supinator when the forearm is flexed (Figs 8.3b and c, All screwing movements are done with it 8.6, 8.7) It is a flexor of the elbow The short head is a flexor of the arm The long head prevents upwards displacement of the head of the humerus It can be tested against resistance as shown in Fig. 8.8 3. Brachialis Musculocutaneous nerve is motor Flexes forearm at the elbow joint Radial nerve is proprioceptive Root Value Relations Upper Limb The root value of musculocutaneous nerve is ventral In the lower part of the axilla: It accompanies the third rami of C5–C7 segments of spinal cord. part of the axillary artery and has the following relations. Anteriorly: Pectoralis major. Origin, Course and Termination Posteriorly: Subscapularis. Musculocutaneous nerve arises from the lateral cord of brachial plexus in the lower part of the axilla. It Medially: Axillary artery and lateral root of the median nerve (see Fig. 4.9). accompanies the third part of the axillary artery. It then enters the front of arm, where it pierces coracobrachialis Laterally: Coracobrachialis (see Fig. 4.9). muscle. Musculocutaneous nerve leaves the axilla, and enters 1 Musculocutaneous nerve runs downwards and the front of the arm by piercing the coracobrachialis Section laterally between biceps brachii and brachialis muscles (Fig. 8.6). to reach the lateral side of the tendon of biceps brachii. In the arm: It runs downward and laterally between It terminates by continuing as the lateral cutaneous the biceps brachii and brachialis to reach the lateral side nerve of forearm 2 cm above the bend of the elbow of the tendon of the biceps. It ends by piercing the fascia (Fig. 8.6). 2 cm above the bend of the forearm.  ARM 97 Fig. 8.3a: Short head of biceps brachii and coacobrachialis muscles Fig. 8.3b: The biceps brachii muscle in extended elbow Upper Limb 1 Section Fig. 8.3c: Intracapsular course of long head of biceps brachii muscle  UPPER LIMB 98 Branches and Distribution Muscular branches: It supplies the following muscles of the front of the arm. i. Coracobrachialis ii. Biceps brachii, long and short heads iii. Brachialis (Figs 8.6 and 8.7). Cutaneous branches: Through the lateral cutaneous nerve of the forearm, it supplies the skin of the lateral side of the forearm from the elbow to the wrist including the ball of the thumb (see Fig. 7.1a). Articular branches: i. The elbow joint through its branch to the brachialis. Fig. 8.4: The precise mode of insertion of the biceps brachii ii. The shoulder joint through a separate branch which muscle enters the humerus along with its nutrient artery. Communicating branches: The musculocutaneous nerve through lateral cutaneous nerve of forearm communicates with the neighbouring nerves, namely the superficial branch of the radial nerve, the posterior cutaneous nerve of the forearm, and the palmar cutaneous branch of the median nerve. Upper Limb 1Section Fig. 8.5: The origin and insertion of the brachialis muscle Fig. 8.6: The course of the musculocutaneous nerve  ARM 99 Fig. 8.7: Transverse section passing through the lower one-third of the arm Median Nerve DISSECTION Median nerve is closely related to the brachial artery Make an incision in the middle of deep fascia of the throughout its course in the arm (Fig. 8.9). upper arm right down up to the elbow joint. Reflect the In the upper part, it is lateral to the artery; in the flaps sideways. middle of the arm, it crosses the artery from lateral to The most prominent muscle seen is the biceps the medial side; and remains on the medial side of the brachii. Deep to this, another muscle called brachialis artery right up to the elbow. is seen easily. In the fascial septum between the two In the arm, the median nerve gives off a branch to muscles lies the musculocutaneous nerve (a branch of the pronator teres just above the elbow and vascular the lateral cord of brachial plexus). Trace the tendinous branches to the brachial artery. long head of biceps arising from the supraglenoid An articular branch to the elbow joint arises at the tubercle and the short head arising from the tip of the elbow. coracoid process of scapula. Identify coracobrachialis muscle on the medial side of biceps brachii. This muscle Ulnar Nerve is easily identified as it is pierced by musculocutaneous nerve. Clean the branches of the nerve supplying all Ulnar nerve runs on the medial side of the brachial the three muscles dissected (refer to BDC App). artery up to the level of insertion of the coraco- brachialis, where it pierces the medial intermuscular septum and enters the posterior compartment of the CLINICAL ANATOMY arm. It is accompanied by the superior ulnar collateral Physician holds the patient’s wrist firmly, not letting it vessels. move. Patient is requested to flex the elbow against At the elbow, it passes behind the medial epicondyle Upper Limb the resistance offered by physician’s hand. One can see where it can be palpated with a finger (Fig. 8.13a). and palpate hardening biceps brachii muscle (Fig. 8.8). Radial Nerve At the beginning of the brachial artery, the radial nerve lies posterior to the artery (see Fig. 4.9). Soon the nerve leaves the artery by entering the radial (spiral) groove on the back of the arm where it is accompanied by the profunda brachii artery (Fig. 8.13a). 1 In the lower part of the arm, the nerve appears Section again on the front of the arm where it lies between the brachialis (medially); and the brachioradialis and extensor carpi radialis longus (laterally) (Fig. 8.17). Its branches will be discussed with the Fig. 8.8: Testing biceps brachii against resistance back of the arm.  UPPER LIMB 100 Biceps reflex: Musculocutaneous nerve is tested by downwards and laterally in the front of arm and crosses biceps reflex. Tap the tendon of biceps with forearm the elbow joint. It ends at the level of the neck of radius pronated and partially extended at the elbow. in the cubital fossa by dividing into its two terminal Normal reflex is jerk-like flexion of elbow joint. branches, the radial and ulnar arteries. Relations Competency achievement: The student should be able to: 1 It runs downwards and laterally, from the medial AN 11.2 Identify and describe origin, course, relations, branches (or side of the arm to the front of the elbow. tributaries), and termination of important nerves and vessels in arm.3 2 It is superficial throughout its extent and is accompanied by two venae comitantes. BRACHIAL ARTERY 3 Anteriorly, in the middle of the arm, it is crossed by Features the median nerve from the lateral to the medial side; Brachial artery is the continuation of the axillary artery. and in front of the elbow, it is covered by the bicipital It extends from the lower border of the teres major aponeurosis and the median cubital vein (Fig. 8.9). muscle to a point in front of the elbow, at the level of 4 Posteriorly, it is related to: the neck of the radius, just medial to the tendon of the i. The triceps brachii biceps brachii. ii. The radial nerve and the profunda brachii artery. Beginning, Course and Termination 5 Medially, in the upper part, it is related to the ulnar Brachial artery begins at the lower border of teres major nerve and the basilic vein, and in the lower part to muscle as continuation of axillary artery. It runs the median nerve (Figs 8.9a and b). Upper Limb 1Section Figs 8.9a and b: The course and relations of the brachial artery  ARM 101 Figs 8.10a and b: Anastomoses around the elbow joint 6 Laterally, it is related to the coracobrachialis, Anastomoses around the Elbow Joint the biceps brachii and the median nerve in its upper Anastomoses around the elbow joint link the brachial part; and to the tendon of the biceps brachii at the artery with the upper ends of the radial and ulnar arteries. elbow (Figs 8.9a and b). They supply the ligaments and bones of the joint. The 7 At the elbow, the structures from the medial to the anastomoses can be subdivided into the following parts. lateral side are: In front of the lateral epicondyle of the humerus, the i. Median nerve anterior descending (radial collateral) branch of the ii. Brachial artery profunda brachii anastomoses with the radial recurrent iii. Biceps brachii tendon branch of the radial artery (Figs 8.10a and b). iv. Radial nerve on a deeper plane (MBBR). Behind the lateral epicondyle of the humerus, the posterior descending branch of the profunda brachii Branches artery (middle collateral) anastomoses with the 1 Unnamed muscular branches. interosseous recurrent branch of the posterior Upper Limb 2 The profunda brachii artery arises just below the teres interosseous artery. major and accompanies the radial nerve. In front of the medial epicondyle of the humerus, the 3 The superior ulnar collateral branch arises in the upper inferior ulnar collateral branch of the brachial artery part of the arm and accompanies the ulnar nerve anastomoses with the anterior ulnar recurrent branch (Figs 8.10a and b). of the ulnar artery. 4 A nutrient artery is given off to the humerus. Behind the medial epicondyle of the humerus, the 5 The inferior ulnar collateral (or supratrochlear) branch superior ulnar collateral branch of the brachial artery arises in the lower part and takes part in the anastomoses with the posterior ulnar recurrent branch of the ulnar artery. 1 anastomoses around the elbow joint. 6 The artery ends by dividing into two terminal Section branches, the radial and ulnar arteries. DISSECTION Dissect the brachial artery as it lies on the medial side Competency achievement: The student should be able to: of the upper part of the arm medial to median nerve AN 11.6 Describe the anastomoses around the elbow joint.4 and lateral to ulnar nerve (Figs 8.9a and b).  UPPER LIMB 102 In the lower half of the upper arm, the brachial artery is seen lateral to the median nerve as the nerve crosses the brachial artery from lateral to medial side. Note that the median nerve and brachial artery are forming together a neurovascular bundle (refer to BDC App). Ulnar nerve accompanied by the superior ulnar collateral branch of the brachial artery will be dissected later as it reaches the posterior (extensor) compartment of the upper arm after piercing the medial intermuscular septum (refer to BDC App). Look for the radial nerve on the posterior aspect of artery before it enters the radial groove. Clean the branches of brachial artery and identify other arteries which take part in the arterial anastomoses around the elbow joint. Fig. 8.11: Blood pressure being taken CLINICAL ANATOMY Brachial pulsations are felt or auscultated in front of the elbow just medial to the tendon of biceps for recording the blood pressure (Fig. 8.11). Figure 8.12 shows other palpable arteries. Although the brachial artery can be compressed anywhere along its course, it can be compressed most favourably in the middle of the arm, where it lies on the tendon of the coracobrachialis. Blood for blood gas analysis is collected from brachial artery. Changes at the Level of Insertion of Coracobrachialis 1 Bone: The circular shaft becomes triangular below this level. 2 Fascial septa: The medial and lateral intermuscular septa become better defined from this level down (Fig. 8.5). 3 Muscles: i. Deltoid and coracobrachialis are inserted at this level (Fig. 8.3a). ii. Upper end of origin of brachialis. Upper Limb iii. Upper end of origin of the medial head of triceps brachii. 4 Arteries: i. The brachial artery passes from the medial side of the arm to its anterior aspect. ii. The profunda brachii artery runs in the spiral groove and divides into its anterior descending/ radial collateral artery and posterior descending/ middle collateral branches (Fig. 8.9). Fig. 8.12: Palpable arteries in the body 1 iii. The superior ulnar collateral artery originates Section from the brachial artery, and pierces the medial ii. Two venae comitantes of the brachial artery may intermuscular septum along with the ulnar nerve. unite to form one brachial vein. iv. The nutrient artery of the humerus enters the bone. 6 Nerves: 5 Veins: i. The median nerve crosses the brachial artery from i. The basilic vein pierces the deep fascia (Fig. 8.13b). the lateral to the medial side (Fig. 8.9).  ARM 103 Figs 8.13a and b: Changes in positions of nerve, veins and arteries ii. The ulnar nerve pierces the medial intermuscular septum with the superior ulnar collateral artery and goes to the posterior compartment (Fig. 8.9). iii. The radial nerve pierces the lateral intermuscular septum with the anterior descending (radial collateral) branch of the profunda brachii artery and passes from the posterior to the anterior compartment (Fig. 8.13a). iv. The medial cutaneous nerve of the arm pierces the deep fascia (Fig. 8.13b). v. The medial cutaneous nerve of the forearm pierces the deep fascia (Fig. 8.13b). Competency achievement: The student should be able to: Upper Limb AN 11.5 Identify and describe boundaries and contents of cubital fossa.5 CUBITAL FOSSA Features Cubital (Latin cubitus, elbow) fossa is a triangular hollow situated on the front of the elbow. (It is homologous Fig. 8.14: Boundaries of the right cubital fossa 1 with the popliteal fossa of the lower limb situated on the back of the knee.) Section Medially – Lateral border of the pronator teres. Boundaries Base – It is directed upwards, and is represented Laterally – Medial border of the brachioradialis by an imaginary line joining the front of (Fig. 8.14). two epicondyles of the humerus.  UPPER LIMB 104 Apex – It is directed downwards, and is formed by the area where brachioradialis crosses the pronator teres muscle. Roof The roof of the cubital fossa (Fig. 8.15) is formed by: a. Skin b. Superficial fascia containing the median cubital vein joining the cephalic and basilic veins. The lateral cutaneous nerve of the forearm lies along with cephalic vein and the medial cutaneous nerve of the forearm along with basilic vein. c. Deep fascia d. Bicipital aponeurosis Floor It is formed by: i. Brachialis (Figs 8.16a and b) ii. Supinator surrounding the upper part of radius Contents The fossa is actually very narrow. The contents described are seen after retracting the boundaries. From medial to the lateral side, the contents are as follows: 1 The median nerve: It gives branches to flexor carpi radialis, palmaris longus, flexor digitorum superficialis and leaves the fossa by passing between Figs 8.16a and b: The floor of the cubital fossa is formed by the two heads of pronator teres (Fig. 8.18). the brachialis and supinator muscles: (a) Surface view, and (b) cross-sectional view Upper Limb 1 Fig. 8.17: Contents of the right cubital fossa; mnemonic—MBBR Section 2 The termination of the brachial artery, and the beginning of the radial and ulnar arteries lie in the fossa. The radial artery is smaller and more superficial than Fig. 8.15: Structures in the roof of the right cubital fossa the ulnar artery. It gives off the radial recurrent branch.  ARM 105 4 The radial nerve: It descends medial to lateral epicondyle to enter cubital fossa. In the fossa, it gives off the posterior interosseous nerve or deep branch of the radial nerve which gives branches to extensor capri radialis brevis and supinator. Then it leaves the fossa by piercing the supinator muscle (Fig. 8.18). The remaining superficial branch runs in the front of forearm for some distance. DISSECTION Identify the structures (see text) present in the roof of a shallow cubital fossa located on the front of the elbow. Separate the lateral and medial boundaries formed respectively by the brachioradialis and pronator teres muscles (Figs 8.14 and 8.19). Clean the contents: i. Median nerve on the medial side of brachial artery. ii. Terminal part of brachial artery bifurcating into radial Fig. 8.18: Contents of right cubital fossa (schematic) and ulnar arteries (refer to BDC App). iii. The tendon of biceps brachii muscle between the brachial artery and radial nerve. The ulnar artery goes deep to both heads of pronator iv. The radial nerve on a deeper plane on the lateral teres and runs downwards and medially, being side of biceps tendon. separated from the median nerve by the deep head Identify brachialis and supinator muscles, forming of the pronator teres (Fig. 8.19). the floor of cubital fossa. Ulnar artery gives off the anterior ulnar recurrent, the posterior ulnar recurrent, and the common CLINICAL ANATOMY interosseous branches (Fig. 8.10). The common interosseous branch divides into the The cubital region is important for the following anterior and posterior interosseous arteries, and reasons: latter gives off the interosseous recurrent branch. a. The median cubital vein is often the vein of 3 The tendon of the biceps brachii (Fig. 8.17). choice for intravenous injections (see Fig. 7.8). It is used for introducing cardiac catheters to get sample of blood from various chambers of heart. b. The blood pressure is universally recorded by auscultating the brachial artery in front of the elbow (Fig. 8.11). The anatomy of the cubital fossa is useful while dealing with the fracture around the elbow, like Upper Limb the supracondylar fracture of the humerus. POSTERIOR COMPARTMENT Features The region contains the triceps muscle, the radial nerve and the profunda brachii artery. The nerve and artery run through the muscle. The ulnar nerve runs through 1 the lower part of this compartment. Section Competency achievement: The student should be able to: AN 11.1 Describe and demonstrate muscle groups of upper arm with emphasis on biceps and triceps brachii. Fig. 8.19: Contents of the cubital fossa seen in cross-section Biceps has been discribed in Tables 8.1 and 8.2.6  UPPER LIMB 106 TRICEPS BRACHII MUSCLE medial head is inserted partly into the superficial Origin tendon, and partly into the olecranon process. Although the medial head is separated from the capsule of the Triceps brachii muscle arises by the following three elbow joint by a small bursa, a few of its fibres are heads (Figs 8.20a and b). inserted into this part of the capsule: This prevents 1 The long head arises from the infraglenoid tubercle nipping of the capsule during extension of the arm. of the scapula; it is the longest of the three heads These fibres are referred to as the articularis cubiti, or as (Fig. 8.21). the subanconeus. 2 The lateral head arises from an oblique ridge on the upper part of the posterior surface of the humerus, Nerve Supply corresponding to the lateral lip of the radial (spiral) Each head receives a separate branch from the radial groove (Fig. 8.20a and b). nerve (C7, C8). The branches arise in the axilla and in 3 The medial head arises from a large triangular area on the radial groove. the posterior surface of the humerus below the radial groove, as well as from the medial and lateral Actions intermuscular septa. At the level of the radial The triceps is a powerful active extensor of the elbow. groove, the medial head is medial to the lateral head The long head causes extension and adduction of arm (see Figs 2.14a and b). at shoulder joint. It supports the head of the humerus in the abducted position of the arm. Gravity extends Insertion the elbow passively. The long and lateral heads converge and fuse to form a Electromyography has shown that the medial head superficial flattened tendon which covers the medial of the triceps is active in all forms of extension, and the head and are inserted into the posterior part of the actions of the long and lateral heads are minimal, except superior surface of the olecranon process (Fig. 8.20). The when acting against resistance. Upper Limb 1Section Figs 8.20a and b: The triceps brachii muscle  ARM 107 Fig. 8.21: Transverse section through the arm a little below the insertion of the coracobrachialis and deltoid showing arrangement of three heads of the triceps, and the radial nerve in the radial groove DISSECTION Reflect the skin of back of arm to view the triceps brachii muscle. Define its attachments and separate the long head of the muscle from its lateral head. Radial nerve will be seen passing between the long head of triceps and medial border of the humerus. Note the continuity of radial nerve up to axilla. Carefully cut through the lateral head of triceps to expose radial nerve along with profunda brachii vessels. Note that the radial nerve lies in the radial groove, on the back of humerus, passing between the lateral head of triceps above and its medial head below. In the lower part of arm, the radial nerve lies on the front of elbow just lateral to the brachialis, dividing into two terminal branches in the Fig. 8.22: Testing triceps brachii against resistance cubital fossa (refer to BDC App). The ulnar nerve (which was seen in the anterior compartment of arm till its middle) pierces the medial Origin, Course and Termination intermuscular septum with its accompanying vessels, Radial nerve is given off from the posterior cord in the reaches the back of elbow and may easily be palpated lower part of axilla. on the back of medial epicondyle of humerus. 1 It runs behind third part of axillary artery (see Upper Limb Figs 4.7c and d). CLINICAL ANATOMY 2 In the arm, it lies behind the brachial artery (Fig. 8.9a). 3 Leaves the brachial artery to enter the lower In radial nerve injuries in the arm, the triceps triangular space to reach the oblique radial sulcus brachii usually escapes complete paralysis because on the back of humerus (Fig. 8.13a). the two nerves supplying it, arise in the axilla. 4 The nerve reaches the lateral side of arm 5 cm below Physician holds the flexed forearm firmly. Patient deltoid tuberosity, pierces lateral intermuscular is requested to extend his elbow against the septum to enter the anterior compartment of arm on resistance of the physician’s hand. The contracting its lateral aspect (Fig. 8.13a). 1 triceps brachii is felt (Fig. 8.22). 5 It descends down medial to the lateral epicondyle Section into cubital fossa. RADIAL NERVE OR MUSCULOSPIRAL NERVE Radial nerve terminates by dividing into a superficial Radial nerve is the largest branch of the posterior cord and a deep branch (posterior interosseous nerve) just of the brachial plexus with a root value of C5–C8 and below the level of lateral epicondyle. These are seen in T1 (see Fig. 4.14). the cubital fossa (Fig. 8.18).  UPPER LIMB 108 Relations It then enters the radial groove with the profunda a. In the lower part of the axilla, radial nerve passes vessels (see Fig. 6.11). downwards and has the following relations. c. In the radial groove, the nerve runs downwards and Anteriorly: Third part of the axillary artery (see Fig. 4.8). laterally between the lateral and medial heads of the triceps brachii, in contact with the humerus (Fig. 8.13a). Posteriorly: Subscapularis, latissimus dorsi and teres At the lower end of the groove, 5 cm below the deltoid major. tuberosity, the nerve pierces the lateral intermuscular Laterally: Axillary nerve and coracobrachialis. septum and passes into the anterior compartment of Medially: Axillary vein (see Fig. 4.9). the arm (Fig. 8.17) to reach the cubital fossa where it b. In the upper part of the arm, it continues behind the ends by dividing into superficial and deep branches. brachial artery, and passes posterolaterally (with the profunda brachii vessels) through the lower Branches and Distribution triangular space, below the teres major, and between Various branches of radial nerve are shown in the long head of the triceps brachii and the humerus. Figs 8.23a–c. Upper Limb 1Section Figs 8.23a and b: Distribution of right radial nerve  ARM 109 or even the pressure of the crutch (crutch paralysis) (Figs 8.24a and b). b. Fractures of the shaft of the humerus. This results in the weakness and loss of power of extension at the wrist (wrist drop) (Fig. 8.25) and sensory loss over a narrow strip on the back of forearm, and on the lateral side of the dorsum of the hand (Fig. 8.26). Wrist drop is quite disabling, because the patient cannot grip any object firmly in the hand without the synergistic action of the extensors. Fig. 8.23c: Distribution of radial nerve (schematic) Muscular 1 Before entering the spiral groove, radial nerve supplies the long and medial heads of the triceps brachii. 2 In the spiral groove, it supplies the lateral and medial heads of the triceps brachii and the anconeus. 3 Below the radial groove, on the front of the arm, it supplies the brachialis with proprioceptive fibres. The brachioradialis and extensor carpi radialis Figs 8.24a and b: Injury to radial nerve: (a) Saturday night longus are supplied with motor fibres (Fig. 8.23a). palsy, and (b) crutch paralysis Cutaneous Branches 1 In the axilla, radial nerve gives off the posterior cutaneous nerve of the arm which supplies the skin on the back of the arm (see Fig. 7.1b). 2 In the radial groove, the radial nerve gives off the lower lateral cutaneous nerves of the arm and the posterior cutaneous nerve of the forearm. Upper Limb Articular branches: The articular branches near the elbow supply the elbow joint. Competency achievement: The student should be able to: AN 11.4 Describe the anatomical basis of Saturday night paralysis.7 AN 12.13 Describe the anatomical basis of wrist drop.8 CLINICAL ANATOMY 1 The radial nerve is very commonly damaged in Section the region of the radial (spiral) groove. The common causes of injury are as follows. a. Sleeping in an armchair with the limb hanging by the side of the chair (Saturday night palsy), Fig. 8.25: Wrist drop  UPPER LIMB 110 Mnemonics Cubital fossa contents MBBR From medial to lateral: Median nerve Brachial artery Tendon of Biceps Radial nerve Biceps brachii muscle: Origins “You walk shorter to a street corner. You ride longer on a superhighway” Short head originates from coracoid process. Long head originates from the supraglenoid tubercle. FACTS TO REMEMBER Fig. 8.26: Sensory loss over back of forearm and dorsum of Medial root of median nerve crosses the axillary hand artery in front to join lateral root to form the median nerve. PROFUNDA BRACHII ARTERY The order of structures from medial to lateral side in the cubital fossa is median nerve, brachial artery, Profunda brachii artery is a large branch, arising just tendon of biceps brachii and radial nerve. below the teres major. It accompanies the radial nerve through the radial groove, and before piercing the Triceps brachii is the only active extensor of elbow lateral intermuscular septum, it divides into the anterior joint. Gravity extends the joint passively. and posterior descending branches which take part in Biceps brachii is a strong supinator of the flexed the anastomoses around the elbow joint (Fig. 8.10). elbow, besides being its flexor. Branches CLINICOANATOMICAL PROBLEM 1 The radial collateral (anterior descending) artery is one of the terminal branches, and represents the In a motorcycle accident, there was injury to the continuation of the profunda artery. It accompanies middle of back of arm. the radial nerve, and ends by anastomosing with the What nerve is likely to be injured? radial recurrent artery in front of the lateral What muscles are affected? Name five of them. epicondyle of the humerus (Fig. 8.10). What is the effect of injury? 2 The middle collateral (posterior descending) artery is the largest terminal branch, which descends in the Ans: Due to injury to the middle of back of arm, the substance of the medial head of the triceps. It ends radial nerve gets injured. The muscles of arm affected by anastomosing with the interosseous recurrent partially are lateral and medial heads of triceps artery, behind the lateral epicondyle of the humerus brachii. A part of muscle escapes paralysis as it gets Upper Limb (Fig. 8.10). It usually gives a branch which supplied in the axilla. accompanies the nerve to the anconeus. The other muscles affected are the extensors of 3 The deltoid (ascending) branch ascends between the forearm. These are brachioradialis, extensor carpi long and lateral heads of the triceps, and radialis longus and brevis, extensor digitorum and anastomoses with the descending branch of the extensor pollicis longus. posterior circumflex humeral artery. The effect of injury is ‘wrist drop’. 4 The nutrient artery to the humerus is often present. It enters the bone in the radial groove just behind the FURTHER READING 1 deltoid tuberosity. However, it may be remembered Jayakumari S, Rath G, Arora J. Unilateral double axillary and that the main artery to the humerus is a branch of Section double brachial arteries. Embryological basis and clinical the brachial artery. implications. Int J Morph 2006;24(3):463–68. 1–8 From Medical Council of India, Competency based Undergraduate Curriculum for the Indian Medical Graduate, 2018;1:44–80.  ARM 111 1. Describe musculocutaneous nerve under following 3. Write short notes on: headings: a. Changes at the level of insertion of coraco- a. Root value b. Course brachialis c. Branches d. Relations b. Anastomoses around the elbow joint e. Clinical anatomy c. Origin and insertion of triceps brachii muscle 2. Enumerate all the boundaries and contents of cubital fossa. Give the clinical importance of the d. Branches of deep branch of radial nerve. What fossa. is the effect of its injury? 1. Which event does not occur at the insertion of 5. Lateral boundary of cubital fossa is formed by coracobrachialis? which muscle? a. Median nerve crosses brachial artery from the a. Biceps brachii b. Brachioradialis lateral to the medial side c. Brachialis d. Extensor carpi radialis b. Ulnar nerve pierces medial intermuscular septum longus c. Lateral cutaneous nerve of forearm pierces the 6. Fracture of humerus at mid-shaft is likely to cause deep fascia injury to which of the following nerves? d. Radial nerve pierces lateral intermuscular septum a. Median b. Radial 2. Interosseous recurrent artery is a branch of which c. Ulnar d. Musculocutaneous artery? 7. Correct order of structures from medial side to a. Ulnar lateral side in cubital fossa is: b. Common interosseous a. Median nerve, brachial artery, biceps tendon and c. Anterior interosseous radial nerve d. Posterior interosseous b. Median nerve, biceps tendon, radial nerve, 3. Which nerve is felt behind medial epicondyle of branchial artery humerus? c. Median nerve, brachial artery, radial nerve and a. Radial biceps tendon b. Median d. Brachial artery, median nerve, biceps tendon, c. Musculocutaneous radial nerve d. Ulnar 8. Which are the heads of triceps brachii muscle? 4. Which of the following nerve injury leads to wrist a. Long, medial and posterior drop? b. Long, lateral and medial a. Ulnar b. Radial c. Long, lateral and posterior Upper Limb c. Median d. Axillary d. Lateral, medial and posterior 1. c 2. d 3. d 4. b 5. b 6. b 7. a 8. b 1 Section How many compartments are there in the upper Name the events occurring at the level of insertion arm? of coracobrachialis. Name the root value of musculocutaneous nerve. What is name of its cutaneous branch?  UPPER LIMB 112 Name the muscles supplied by musculocutaneous Enumerate the structures forming its roof. nerve. Name the muscles forming floor of the fossa. Which muscle does coracobrachialis correspond to What are the main contents of the fossa? in lower limb? Name the branches of median nerve in the fossa. Name the branches of brachial artery. What is the clinical importance of brachial artery? Name the branches of brachial artery in the fossa. Name the nerves present on the medial side of Name the branches of radial nerve in the fossa. brachial artery in its course in upper part and in What is the clinical importance of bicipital lower part of arm. aponeurosis? How is median nerve formed? Why is it called What is clinical importance of cubital fossa? median nerve? Name the heads of triceps brachii muscle and show Name the branches of median nerve in the arm. their origins and insertion. Name the branches of radial nerve in the axilla. Name the regions through which radial nerve passes. Which movement will be affected in paralysis of the Name the branches of radial nerve in all these regions. musculocutaneous nerve? What is wrist drop? CUBITAL FOSSA What is the course of profunda brachii artery? Name What muscle forms lateral boundary of cubital fossa? its branches. What muscle forms its medial boundary? What does word ‘profunda’ mean? Upper Limb 1Section