5 Neurovascular Systems: Topographical Anatomy
5.1 Surface Anatomy and Superficial Nerves and Vessels: Anterior View
A Surface anatomy of the right upper limb
Anterior view. The palpable bony landmarks of the upper limb are reviewed on p. 241.
B Hand lines and flexion creases on the right palm with the wrist in slight flexion (after Schmidt and Lanz)
The proximal wrist crease, located approximately one finger width from the palm, coincides with the distal epiphyseal lines of the radius and ulna. The distal wrist crease usually overlies the midcarpal joint.
C Schematic structure of the ridged skin on the palm of the hand
The smooth, thin skin of the forearm gives way to the thicker, ridged skin on the palm of the hand. The papillary ridges are particularly high on the palmar skin of the fingers and, at 0.1 to 0.4 mm, are distinctly visible. The ridge pattern (dermatoglyphs) found on the bulbs of the fingers is unique for each individual. The tactile sensitivity of the fingertips is closely linked to the spatial distribution of tactile corpuscles and free nerve endings (e.g., 75–80 Vater–Pacini corpuscles per finger and approximately 100 free nerve endings per square millimeter).
D Superficial cutaneous veins and nerves of the right upper limb
Anterior view. The arrangement of cutaneous veins about the elbow can vary considerably (see p. 358). This dissection does not show the cutaneous arteries that perforate the antebrachial fascia (particularly those arising from the radial artery, see also p. 357).
E Radicular (segmental) cutaneous innervation pattern (dermatomes) in the right upper limb
Anterior view. With the outgrowth of the upper limb during development, the sensory cutaneous segments become elongated in varying degrees to form narrow bands. In the process, segments C5–C7 become separated from the body wall.
F Pattern of peripheral sensory cutaneous innervation in the right upper limb
Anterior view. The territories supplied by the peripheral cutaneous nerves (cutaneous branches) correspond to the areas of cutaneous nerve branching in the subcutaneous connective tissue that are demonstrable by dissection. The area served exclusively by a single nerve and thus rendered completely anesthetic by a lesion is much smaller because the individual sensory territories overlap extensively. Note: The sensory loss following damage to a peripheral nerve shows a completely different pattern than that of a damaged nerve root.
5.2 Surface Anatomy and Superficial Nerves and Vessels: Posterior View
A Surface anatomy of the right upper limb
Posterior view. The palpable bony landmarks of the upper limb are reviewed on p. 241.
B Extension creases on the dorsum of the right hand (after Schmidt and Lanz)
In contrast to the palm, the dorsal surfaces of the hand and fingers bear indistinct extension creases that deepen with maximum dorsiflexion of the hand. The most proximal crease overlies the styloid process of the ulna, while the most distal crease approximately overlies the distal margin of the extensor retinaculum. Unlike the hairless ridged skin of the palm, the dorsum of the hand is covered by smooth, thin, hair-bearing skin.
C Location of the MCP, PIP, and DIP joint spaces
Right hand closed into a fist, radial view.
D Superficial cutaneous veins (subcutaneous veins) and cutaneous nerves of the right upper limb
Posterior view. The epifascial veins of the dorsum of the hand (dorsal venous network) display a highly variable branching pattern. Generally, the epifascial veins are clearly visible beneath the skin, receiving tributaries that include perforating veins from the palmar side of the hand. The cephalic vein on the radial side of the hand provides for most of the dorsal venous drainage, while the basilic vein provides for a lesser degree on the ulnar side. This dissection does not show the main branches of the posterior interosseous artery that perforate the antebrachial fascia on the back of the forearm (see also p. 357).
E Radicular (segmental) cutaneous innervation pattern (dermatomes) in the right upper limb
Posterior view. With the outgrowth of the limb during development, the sensory cutaneous segments become elongated in varying degrees to form narrow bands. As this occurs, segments C5–C7 become separated from the body wall.
F Peripheral sensory cutaneous innervation pattern in the right upper limb
Posterior view. The color-coded areas that are supplied by the peripheral cutaneous nerves (cutaneous branches) correspond to the areas of cutaneous nerve branching in the subcutaneous connective tissue that are demonstrable by dissection. The areas of exclusive non-overlapping innervation of a specific nerve is much smaller.
Note that the sensory loss following damage to a peripheral nerve shows a completely different pattern from that caused by damage to a nerve root (see E).
5.3 The Shoulder Region: Anterior View
A Superficial veins and nerves of the right shoulder and neck region
Anterior view. The skin, platysma, muscle fasciae, and superficial layer of the cervical fascia have been removed in this dissection to demonstrate the branches of the cervical plexus (e.g., the great auricular nerve) and the superficial veins of the lateral and anterior neck. The external jugular vein and anterior jugular vein (not shown) are visible through the skin when the patient is lying supine and the veins are well filled. When right-sided heart failure is present, these veins may be engorged due to the damming back of venous blood and may be visible even when the patient is sitting upright. The cephalic vein crosses the shoulder in the groove between the pectoralis major and deltoid muscles (deltopectoral groove) and empties into the axillary or subclavian vein. This site of entry into the axillary vein, and thus into the deep veins, is visible and palpable on the skin as the infraclavicular fossa. At the level of the lateral border of the first rib, the axillary vein becomes the subclavian vein.
B Relationship of major superficial and deep veins in the neck to the sternocleidomastoid muscle
Anterior view. The internal jugular vein runs almost straight downward from the jugular foramen and unites with the subclavian vein just lateral to the sternoclavicular joint to form the brachiocephalic vein. When its course is projected onto the side of the neck, it follows a line drawn from the earlobe to the medial end of the clavicle. The internal jugular vein is crossed obliquely in its lower third by the sternocleidomastoid muscle, while the external jugular vein runs obliquely downward on the muscle and opens into the subclavian vein.
C Course of the right subclavian artery in the lateral neck region
Anterior view. The sternocleidomastoid and omohyoid muscles and all layers of the cervical fasciae have been removed to demonstrate the deep lateral cervical triangle and the passage of the subclavian artery and brachial plexus through the space between the anterior and middle scalene muscles (interscalene space). At the level of the first rib the subclavian artery becomes the axillary artery, which enters the axilla posterior to the tendon of insertion of the pectoralis minor.
D Origin and branches of the right subclavian artery
E Branches of the subclavian artery: normal anatomy and variants (after Lippert and Pabst)
a Normally (30% of cases), the subclavian artery gives off the following branches:
• Thyrocervical trunk with the inferior thyroid artery, suprascapular artery, and transverse cervical artery
• Vertebral artery
• Internal thoracic artery
• Costocervical trunk
b The transverse cervical artery arises separately from the subclavian artery (30%).
c The internal thoracic artery arises from the thyrocervical trunk (10%).
d The thyrocervical trunk is made up of the inferior thyroid artery, suprascapular artery, and internal thoracic artery (8%).
e The subclavian artery gives off two main branches:
1. One with the inferior thyroid and transverse cervical arteries.
2. One with the internal thoracic and suprascapular arteries (4%).
5.4 The Axilla: Anterior Wall
A The walls and fasciae of the right axilla
Anterior view. With the arm abducted, the axilla (axillary fossa) resembles a four-sided pyramid whose apex is approximately at the center of the clavicle and whose base is represented by the axillary fascia. The walls of the axilla are formed by various muscles and their fasciae:
Anterior wall: The anterior wall of the axilla consists of the pectoralis major and minor and the clavipectoral fascia (the pectoralis minor is not shown here; see C and D).
Posterior wall: This consists of the subscapularis, teres major (not shown here, see p. 308), and latissimus dorsi.
Lateral wall: This is narrow and formed by the intertubercular groove of the humerus.
Medial wall: This is formed by the lateral thoracic wall (ribs 1–4 and associated intercostal muscles) and the serratus anterior.
B The clavipectoral triangle and clavipectoral fascia
Right shoulder, anterior view. The clavicular part of the pectoralis major has been removed. In the clavipectoral triangle bounded by the deltoid, pectoralis major, and clavicle, the cephalic vein runs upward in the deltopectoral groove, pierces the clavipectoral fascia, and drains into the axillary vein at the level of the infraclavicular fossa.
C The axilla after removal of the pectoralis major and clavipectoral fascia
Right shoulder, anterior view. The axillary artery runs approximately 2 cm below the coracoid process and posterior to the pectoralis minor. It relates laterally to the lateral cord of the brachial plexus and medially to the medial cord (both are retracted slightly upward in the drawing). The posterior cord of the brachial plexus, which runs behind the axillary artery, is just visible.
D Location of the superficial and deep thoracic fasciae
Sagittal section through the anterior wall of the right axilla. The clavipectoral fascia, known also as the “deep” thoracic fascia, encloses the pectoralis minor and subclavius muscles and covers the subclavian vein while being fused to its wall. The fascia is made tense by the pectoralis minor. The clavipectoral fascia exerts traction on the vein wall that can keep its lumen patent, thus facilitating venous return to the superior vena cava.
E Schematic transverse section through the right axilla
Superior view. The three muscular walls and the bony lateral wall of the axilla are clearly delineated in this view. Neurovascular structures (axillary artery and vein plus the medial, lateral, and posterior cords of the brachial plexus) traverse the axilla, invested by a fibrous sheath and embedded in the axillary fat.
5.5 The Axilla: Posterior Wall
A Posterior wall of the axilla with the posterior cord and its branches
Right shoulder, anterior view. The medial and lateral cords of the brachial plexus and the axillary vessels have been removed to demonstrate the course of the posterior cord and its branches in the posterior axilla.
B Relationship of the medial, lateral, and posterior cords of the brachial plexus to the axillary artery
Note that the musculocutaneous nerve passes through the coracobrachialis, which aids in locating the nerve. Very rarely, this nerve may be compressed as it pierces the muscle.
C Origin and branches of the axillary artery
Right shoulder, anterior view.
D Axilla with the entire anterior wall removed
Right shoulder, anterior view. The axillary vein has been removed, and the medial and lateral cords of the brachial plexus have been retracted upward to show more clearly the location and course of the posterior cord and its terminal branches, the radial nerve and axillary nerve.
Note the superficial course of the long thoracic nerve on the serratus anterior.
E Branches of the axillary artery: normal anatomy and variants (after Lippert and Pabst)
a Normally (40% of cases), the axillary artery gives off the following branches:
Superior thoracic artery, thoracoacromial artery, lateral thoracic artery, subscapular artery, anterior circumflex humeral artery, and posterior circumflex humeral artery.
b The thoracoacromial artery arises from the lateral thoracic artery (10% of cases).
c Common origin of the lateral thoracic artery and subscapular artery (10% of cases).
d The posterior circumflex humeral artery arises from the subscapular artery (20% of cases).
e Common origin of the anterior and posterior circumflex humeral arteries (20% of cases). The common segment formed by both arteries is termed the common circumflex humeral artery.
5.6 Conduction Anesthesia of the Brachial Plexus: Principle, Pathways, and Administering the Block
A Principle of peripheral conduction anesthesia
Peripheral conduction anesthesia is a regional anesthetic technique that blocks conduction of action potentials. The area under anesthesia is thus distal to the puncture site. It is possible to anesthetize both individual peripheral nerves and the entire plexus.
B Topography of the brachial plexus and anatomic landmarks
The brachial plexus is responsible for the motor and sensory nerve supply of the upper limbs. It is formed from the anterior rami of the spinal nerves C5–T1 (see p. 362). In the course of the plexus, first the trunks are formed, followed by the divisions, and then the cords. The trunks are located at the level of the interscalene space. The divisions are above and behind the clavicle. The cords run infraclavicular and start cranial or lateral to the axillary artery and at the level of the axilla, posterior (posterior cord), lateral (lateral cord), and medial (medial cord) to the axillary artery.
Note the important anatomic landmarks for the individual pathways: sternocleidomastoid, cricoid cartilage, thyroid, anterior and middle scalenes (interscalene space), clavicle, acromion, jugular fossa, infraclavicular fossa (Mohrenheim’s fossa), coracobrachialis, and axillary artery. In addition, it is recommended to memorize the topographic anatomy in relation to the following structures, which could potentially get damaged: phrenic nerve, recurrent laryngeal nerve, cervical or thoracic and cervical sympathetic ganglia (e.g., stellate ganglion), vertebral artery, cervical epidural and subarachnoid space, and pleural dome.
C Brachial plexus sheath and electrical nerve stimulation
From passage through the interscalene space to the axillary region, the entire brachial plexus, together with the accompanying axillary artery and vein, is enclosed by a connective-tissue sheath. Within this sheath, local anesthetic can dissipate more or less evenly, anesthetizing all nerves in this area. In order to target and effectively block one particular nerve, electrical nerve stimulation is performed. A stimulation cannula, only the tip of which is not isolated, emits a defined current pulse. This current pulse can trigger action potentials at the respective motor axons (for more details about the possible responses, see E). With correct positioning of the cannula, ensuing injection of 1 to 2 mL of a suitable local anesthetic should lead to immediate suppression of muscle function (extinction phenomenon).