Upper Limb Anatomy: Shoulder, Arm, and Brachial Plexus - PDF

Image (reuse: Wikimedia creative commons) The axial skeleton is made up of the skull (cranium), the vertebral column, the ribs and the sternum. The upper and lower extremity, or limb, bones (including the pectoral and pelvic girdles) make up the appendicular skeleton. The pectoral (shoulder) girdle...

Image (reuse: Wikimedia creative commons) The axial skeleton is made up of the skull (cranium), the vertebral column, the ribs and the sternum. The upper and lower extremity, or limb, bones (including the pectoral and pelvic girdles) make up the appendicular skeleton. The pectoral (shoulder) girdle includes the scapula and clavicle and has a considerable range of motion. Grant’s Fig. 6.01A The upper extremity is composed of the following regions: the shoulder, arm, forearm, wrist and hand. These are the proper anatomical terms for the parts of the upper extremity. The shoulder is the proximal segment of the limb that overlaps parts of the trunk (thorax and back) and lower lateral neck. Be mindful that the term “arm” (L. brachium) refers to the upper extremity between the shoulder and the elbow; “forearm” (L. antebrachium) refers to the upper extremity between the elbow and the wrist. This terminology is specific and designed to avoid confusion, so practice using it as much as you can! Thieme Anatomy: An Essential Textbook 2nd ed. Fig. 13.3 Two bones make up the pectoral girdle. From proximal to distal, they are the clavicle, the scapula. The clavicle is an s-shaped bone that articulates with the sternum proximally and the scapula distally. Note that it is the only bony attachment of the upper limb to the axial skeleton. The clavicle is the first long bone to start ossification (begins ossifying around week 5-6 via intramembranous ossification) but it is also one of the last long bones to fuse (22-25 years of age). Scale-like ossification center at the sternal end that begins to fuse with the diaphysis (shaft) between 18-25 years – don’t mistake this for a fracture. Thieme Anatomy: An Essential Textbook 2nd ed. 13.4A,C The scapula (shoulder blade) articulates with the clavicle at the acromion and the two bones collectively form the shoulder girdle. Two bony processes, the acromion and the coracoid process, project anteriorly from the scapula. You should be familiar with the other bony features listed on this slide. Thieme Anatomy: An Essential Textbook 2nd ed. 13.4B; Gliroy 3rd ed Fig. 25.2C The scapula rests against the posterior rib cage. The glenoid cavity, a hyaline-lined shallow depression in the scapula, is the site of the glenohumeral joint. Thieme Anatomy: An Essential Textbook 2nd ed. 13.6A,B The humerus is the only bone of the anatomical arm. For now we will focus on the features of the proximal humerus. The anatomical neck is the most proximal. The surgical neck is slightly more distal, and is a more common site of fractures than the anatomic neck. The deltoid tuberosity is more distal and is found on the lateral aspect of the humerus. At the head of the humerus, the greater tubercle is lateral and the lesser tubercle is anterior (tuberosity and tubercle are essentially fancy words for “bump”). The groove running between the two tubercles is called the intertubercular (or biciptal) groove. Thieme Anatomy: An Essential Textbook 2nd ed. Fig. 13.3; Gliroy 3rd ed. Fig 25.11A There is only one bony articulation between the upper extremity and the axial skeleton: the sternoclavicular joint. The clavicle also articulates with the scapula at the acromioclavicular (“AC”) joint, a synovial joint with limited motion. Note the position of the scapula on the ribs. Movements of the shoulder girdle require some mobility at the AC joint. The glenohumeral or shoulder joint is a ball and socket type in which the socket (the glenoid cavity) is decidedly shallow such that the ball or the head of the humerus does not really penetrate the socket. Gliroy 3rd ed. Fig 25.9 The sternoclavicular joint (SC) is a saddle joint (type of synovial joint). The SC joint is divided into two compartments by a fibrocartilaginous disc. The disc is firmly attached to the sternoclavicular and interclavicular ligaments, strengthening the joint. While strong, the SC joint is significantly mobile to allow movements of the pectoral girdle and upper limbs. Thieme Anatomy: An Essential Textbook, 2nd ed. Fig 14.10 The acromiolclavicular joint (AC joint) is a plane joint, a synovial joint with limited motion. The acromial end of the clavicle articulates with acromion of the scapula. The articular surfaces are covered in fibrocartilage and are separated by an incomplete wedge-shaped articular disc. Gliroy 3rd ed Box 25.3; Simon’s Emergency Orthopedics, 7e, Fig. 16-37 The acromioclavicular and coracoclavicular ligaments are important for maintaining shoulder stability. Falling on an outstretched arm or shoulder frequently causes dislocation of the acromioclavicular joint and damage to the coracoclavicular ligament. Shoulder separation occurs at the AC joint whereas shoulder dislocation occurs at the glenohumeral joint. In a fall capable of separating the AC joint a person will often fracture the clavicle, the most common place being between the middle and lateral thirds. A “complete shoulder separation” is the rupture of all three ligaments (the acromioclavicular, the trapezoid, and conoid), while a “partial shoulder separation” is the rupture of only the acromioclavicular ligament. In either event, surgical intervention is often indicated to repair the torn ligaments followed by physical therapy to rebuild strength and stability in the shoulder. Thieme Anatomy: An Essential Textbook 2nd ed. Fig. 14.201; Table 14.5, Acland’s Video Atlas Netter (4th ed.) 423D The glenohumeral joint is a synovial joint; the articular surfaces of the bones are covered by hyaline cartilage. The cartilaginous surfaces are actually in contact with each other (even though here they appear separated for emphasis). The synovial or joint cavity contains synovial fluid secreted by the synovial membrane. The glenohumeral or shoulder joint is a ball-and-socket type synovial joint in which the socket -- the glenoid cavity -- is relatively shallow such that the ball or the head of the humerus is not surrounded by the socket. The glenoid cavity is somewhat deepened by the fibrocartilaginous glenoid labrum. The head can rotate and slide loosely in many directions, which makes the joint quite unstable. It is the surrounding ligaments and muscles which act to stabilize this joint. Note the subdeltoid (sub-acromial) bursa between the supra and infraspinatus muscles and the acromion and the coracoacromial ligament. This bursa often gets irritated and inflamed (called bursitis). Simon’s Emergency Orthopedics, 7e, Fig. 16–47: The shoulder, with its wide range of motion and shallow glenoid, is inherently unstable. As a consequence, shoulder dislocation is a common joint dislocation presenting to the ED, representing approximately 50% of all major dislocations seen by the emergency physician. The most frequent location of a glenohumeral joint dislocation is anterior, accounting for 95% of cases. Approximately 70% of all anterior dislocations of the shoulder occur in patients younger than 30 years. There are three types of anterior dislocation: subclavicular, subcoracoid, and subglenoid. In 90% of cases, the humeral head is in a subcoracoid location. Movements of the arm occur around three perpendicular axes (i.e. the x, y, and z axes). Shoulder flexion lifts the upper limb anteriorly. Shoulder extension lifts the upper limb posteriorly. Shoulder abduction (AB‐duction) lifts the upper limb laterally (think, “help I’m being AB-ducted!” to remember this motion). Shoulder adduction (ADduction) brings the upper limb back to anatomical position (i.e, it adds the upper limb back to the body). Lateral (external) rotation of the shoulder rotates the arm laterally, such that the hand is lateral. Medial (internal) rotation of the shoulder rotates the arm medially, such that the hand is medial. Circumduction is complex and involves a combination of shoulder flexion/extension and abduction/adduction. Schuenke, Atlas of Anatomy Vol. 1, 2nd Ed., Fig 5.57 Df, Ca; 20.480 B The force a muscle exerts at a joint axis depends on a number of factors including the size and shape, the angle of pull relative to the axis, the attachement points, and the position of the body during muscle recruitment. All muscles help to stabilize the joint they cross Gilroy 2nd ed. Fig. 21.23B,C,D In addition to the superficial muscles of the back which insert on the scapula and move it, there are muscles which originate on the scapula and insert on the proximal humerus to move the arm. The most superficial muscle is the deltoid, which originates in a “U-shaped” fashion from the lateral ⅓ of the clavicle, the acromion, and the spine of the scapula to insert on the deltoid tuberosity of the lateral humeral shaft. The deltoid creates the normal rounded surface anatomy of the shoulder. It is the major abductor of the arm and is innervated by the axillary nerve. **Note that the deltoid abducts from 15˚ onwards, with another muscle (supraspinatus) responsible for abducting the first 15˚.** Origin/attachment point: Spine of the scapula, acromion, lateral 1/3 of clavicle Insertion/attachment point: Deltoid tuberosity of humerus Nerve): Axillary nerve Fx(function): Abducts arm; anterior fibers can flex arm, posterior fibers can extend arm Gilroy 2nd ed. Fig. 21.17. 21.24E The four rotator cuff muscles are deep to the deltoid. Three of the muscles (supraspinatus, infraspinatus, and teres minor) originate from the posterior surface of the scapula and insert on the greater tubercle of the humerus, a lateral structure. The remaining muscle (subscapularis) originates from the anterior surface of the scapula and inserts on the lesser tubercle, an anterior structure. These four muscles surround the glenohumeral joint and provide stability. The supraspinatus initiates the first 15˚ of abduction; the infraspinatus is a lateral (external) rotator of the humerus. Both are innervated by the suprascapular nerve. The teres minor is also a lateral rotator but is innervated by the axillary nerve. The subscapularis is a medial (internal) rotator and is innervated by the upper and lower subscapular nerves. The tendons of insertion of the rotator cuff muscles form a musculotendinous cuff around the shoulder joint. Repeated abduction and flexion (such as the throwing motion of a pitcher) cause stress on the tendons as they rub on the acromion and coracoacromial ligament. This may lead to cuff tears or rupture. The tendon of the supraspinatus is most vulnerable to injury. Fig. 1.16 in Schunke et al., Thieme, Atlas of Anatomy, Volume 1 Supraspinatus (impingement) syndrome. If the supraspinatus tendon becomes thickened due to calcification or other degenerative changes, it can be caught underneath the acromion, impinging upon the subacromial bursa, when the arm is abducted. Pain from this supraspinatus, or impingement, syndrome occurs between 60 and 120° of abduction. Gilroy 2nd ed. Fig. 21.22B The teres major is not a rotator cuff muscle. It originates from the inferior angle of the scapula and inserts on the medial lip of the intertubercular groove of the humerus. Teres major adducts and medially rotates the humerus and is innervated by the lower subscapular nerve. There are three muscles of the arm arising from the scapula which will be discussed in a bit – for now notice the long head of the triceps brachii which originates from the infraglenoid tubercle of the scapula. The blood supply and innervation of all these shoulder (and arm) muscles arise from structures passing anterior to the shoulder joint. There must be spaces for them to pass through to become posterior… Thieme Anatomy: An Essential Textbook, 2nd ed. Fig. 14.13A There are three such spaces: the quadrangular space, the triangular space, and the triangular interval. The borders of these spaces are created by the teres minor and major, the long head of the triceps and the shaft of the humerus. You should know the borders of these three spaces. It may be helpful to remember that the long head of the triceps muscle passes anterior to the teres minor but posterior to the teres major as it descends from its origin on the infraglenoid tubercle of the scapula. Fig. 5.9, Thieme, Schunke et al., Atlas of Anatomy, Vol. 1 General… The posterior circumflex humeral artery accompanies the axillary nerve through the quadrangular space. The circumflex scapula artery is visible in the triangular space. The radial nerve and deep artery of the arm (profunda brachii) pass through the triangular interval. The suprascapular vessels and nerve cross the neck to reach the posterior surface of the scapula via the suprascapular notch, with the artery passing superficial to the transverse scapular ligament and the nerve passing deep. Mnemonic to remember the artery as superficial and nerve as deep to the transverse scapular ligament: the “Army goes over the bridge; Navy goes under the bridge.” They supply both the supra- and infraspinatus muscles. Gilroy 3nd ed. Fig 24.3 As is the case with most joints, the shoulder has a rich vascular anastomosis. This supplies not only the 16 muscles attaching to the scapula and other shoulder muscles, but also provides collateral circulation to the upper limb should the proximal part of the axillary artery became occluded. i.e. the axillary artery may be bypassed by anastomoses between the suprascapular, circumflex scapular arteries, and dorsal scapular. Gilroy 3rd ed. Fig. 25.29B There are muscles that do not originate on the scapula and yet produce motion of the shoulder joint, such as the latissimus dorsi. Recall that the latissimus dorsi originates from the spinous processes of lower thoracic and lumbar vertebrae, iliac crest, sacrum and inserts into the medial floor of the intertubercular groove, anterior and slightly superior to the insertion of the teres major. It is a powerful extensor, adductor and medial rotator the humerus and is innervated by the thoracodorsal nerve. Gilroy 3rd ed. Fig 25.27A; Drake 7.3 The trapezius muscle is a broad muscle with multiple attachment points. Gilroy 3rd ed. 4.18, Fig 25.27A When the trapezius contracts, it moves the scapula against the chest wall. Since the fibers of the trapezius are oriented in different directions, they can move the scapula in more than one direction. The innervation of the trapezius is the accessory nerve. This nerve is a cranial nerve (CN XI) and thus trapezius is an exception to the general rule that the superficial extrinsic muscles are innervated by ventral rami. Gilroy 3rd ed. Fig 25.28B O/attachment point: Spinous processes of lower cervical and upper thoracic vertebrae I/attachment point: Medial border of scapula (rhomboid minor superior to the spine; rhomboid major inferior to the spine) N: Dorsal scapular nerve Fx: Retracts and medially rotates scapula remember that the “R-homboids R-etract”! Gilroy 3rd ed. Fig 25.28B O/attachment point: Transverse processes of upper cervical vertebrae I/attachment point: Superior angle of scapula N: Dorsal scapular nerve Fx: Elevates scapula Gilroy 2nd ed. Fig. 24.12C; Sherman SC. Simon’s Emergency Orthopedics, 7e Fig. 16-80 The serratus anterior originates from the lateral aspect of the upper 8 or 9 ribs and inserts on the medial costal border of the scapula. It protracts and laterally rotates the scapula. It is innervated by the long thoracic nerve which travels along its surface. **Clinical correlation: Injury to the long thoracic nerve will paralyze or weaken the serratus anterior muscle. This nerve is injured due to its length and superficial course. Clinically, this injury is noted by an unusual prominence of the medial and inferior borders of the scapula, commonly referred to as the “winged scapula”. The most common cause of this injury is overuse. Other causes include acute trauma, either blunt or penetrating, and the improper use of axillary crutches. The cause is idiopathic in 17% of cases. Gilroy 2nd ed. Fig. 21.19A,B The pectoralis major originates on the anterior thoracic wall and inserts on the lateral lip of the intertubercular groove. It flexes, adducts and medially rotates the humerus. Innervation is by both the lateral and medial pectoral nerves. Pectoralis minor lies deep to the pectoralis major and does not directly participate in the movement of the humerus. The deltopectoral groove lies between the medial border of the anterior deltoid and the lateral edge of the pectoralis major. The cephalic vein, a major route for blood returning to the heart from the upper extremity, lies within this groove. **the cephalic vein is a frequently utilized site for venous access, particularly for cardiac pacemakers and subcutaneous venous access ports. Thieme Anatomy: An Essential Textbook 2nd ed. Fig. 14.5; Gilroy 3rd ed. Fig. 24.1B The axilla (aka, the armpit) is a densely packed area of nerves and vessels traveling between the torso and upper extremity. In the image above, the axilla is suggested by the translucent blue shape. It is generally pyramidal in shape with its apex near the clavicle and first rib, and its floor is the axillary skin fold. The shape of the axilla varies depending upon the position of the arm. Borders of the axilla Anteriorly: the pectoralis muscles (major and minor) Posteriorly: latissimus dorsi, teres major, long head of the triceps and subscapularis Medially: lateral thoracic wall and serratus anterior Laterally: the intertubercular groove of the humerus Schuenke, Vol 1 2nd ed. Fig. 18.348; Gilroy 2nd ed. Fig 24.34B The major arteries and nerves to the upper extremity as well as the veins and lymphatics draining the extremity pass through the axilla. They are contained within the axillary sheath, an extension of the prevertebral fascia of the cervical (neck) region. It is partially suggested here by the green cylinder. **Note: local anesthetic agents injected within this fascial sheath are contained by it and permit a good regional anesthetic “block” of the brachial plexus nerves. Schuenke, Vol 1, 2nd ed. Fig. 17.354 The subclavian artery, which passes superior to the first rib and in between the anterior and middle scalene muscles, changes its name to the axillary artery at the lateral border of the first rib and continues distally through the axilla to the inferior border of the teres major muscle where its name then changes to the brachial artery. Gilroy 2nd. Ed Fig. 24.1 The axillary artery has three parts defined by the pectoralis minor. The first is part is proximal to the pectoralis minor, the second posterior to, and the third distal to it. The first, second and third parts have 1, 2 and 3 branches respectively. The artery of the first portion is the 1) superior thoracic. The arteries of the second portion are the 1) thoracoacromial and the 2) lateral thoracic; of the third portion the 1) subscapular and the 2) anterior and posterior circumflex humeral. The thoracoacromial artery is the common origin of four branches which supply the anterior shoulder area and are not important to memorize individually: acromial, clavicular, deltoid and pectoral). Schuenke Vol.1 2nd ed. Fig. 18.379C The axillary vein, formed by the merger of the brachial and basilic veins, starts at the inferior border of the teres major muscle and ends at the lateral border of the 1st rib where its name changes to the subclavian vein. It is situated anteromedial to the axillary artery in anatomic position and anteroinferior if the arm is abducted. The cephalic vein empties into the axillary vein slightly lateral to the 1st rib. Netter 418. The brachial plexus is created by spinal nerves from spinal cord levels C5 through T1 and contains roots, which are ventral rami, then trunks, divisions, cords, and finally branches (mnemonic = “Rob Thomas Drinks Cold Beer”). The brachial plexus extends through the neck and axilla to supply the upper limb. Each grossly visible nerve contains thousands of axons of nerve fibers (cells) encased in a common epineurium (like a telephone cable). Grant’s Dissector Fig. 6.13; Gilroy 2nd ed Fig. 24.11B The three cords surround the axillary artery and are named according to their relation to that artery in the anatomical position. Repeatedly drawing the plexus is a highly effective and strongly suggested way to gain schematic mastery. I have posted a blank brachial for you to practice labeling, but drawing it from scratch is even better. Branches from the roots: dorsal scapular, long thoracic Branches from trunks: suprascapular Branches from cords Lateral=lateral pectoral Post=upper, lower subscapularis, and thoracodorsal (also known as the middle subscapular) Medial=medial pectoral, medial brachial cutaneous, medial antebrachial cutaneous NO branches from the divisions Terminal branches-radial, axillary, median, ulnar and musculocutaneous You should obtain a good working knowledge of the brachial plexus (C5 - T1) dermatomes on the anterior and posterior upper extremity and fingers. Note that a dermatome is not the same thing as cutaneous innervation. A cutaneous nerve supplies an area of the skin that is related to a peripheral nerve (not a single dorsal root). Any given cutaneous nerve might contain fibers from several individual spinal nerves. Therefore, cutaneous nerve areas and dermatome areas overlap but are not the same thing. A cutaneous nerve area is generally broader and wider than an area supplied by only a single spinal (dermatome) nerve. To review, the humerus is the single bone of the arm and the head of the humerus articulates with the glenoid fossa of the scapula. Proximal features include the anatomical neck, which is directly distal to the head of the humerus, the lesser tubercle anteriorly, the greater tubercle on the lateral aspect, and the intertubercular (bicipital) groove on the anterior side between the greater and lesser tubercles. At the distal end of the humerus the capitulum is lateral for articulation with the radius of the forearm, and the trochlea is medial for articulation with the ulna. Small fossa allow full flexion and extension of the forearm at the elbow. They are the radial and coronoid fossa anteriorly and the olecranon fossa posteriorly. The prominences of the distal humerus on the medial and lateral side of the elbow are the medial and lateral epicondyles, respectively. Supracondylar ridges extend superiorward from the epicondyles. The epicondyles and supracondylar ridges are attachments for muscles of the forearm. Finally, there's a groove (the radial groove) in the medial aspect of the humerus for the radial nerve. Thieme Anatomy: An Essential Textbook Fig. 14.35A In the limbs, there is a layer of superficial fascia directly beneath the skin. Directly covering muscles there is a thin but stronger sheet of deep fascia that surrounds all of the deep structures. Most major nerves and arteries are contained in a perivascular sheath, while individual muscles are also surrounded by deep fascia. Most limbs are divided into compartments, with a thicker layer of fascia segregating groups of muscles. This is termed an intermuscular septum, and there is an intermuscular septum that separates the arm into an anterior, flexor compartment and a posterior, extensor compartment. **Clinical correlation—compartment syndrome: The deep fasciae (particularly of the leg, the tibial, fibular and calf) are not expansible. Pressure buildup within these compartments can cause ischaemia (a restriction in blood supply) as the low pressure blood vessels (veins and capillaries) are compressed, causing tingling and numbness as intracompartmental nerves are compromised. Ischaemia also causes muscle damage leading to further swelling, and if untreated the compartment contents may die. Compartment syndrome can also be caused by blood leaking into the tissues via traumatic injury. A fasciotomy (making a cut in the deep fascia covering the compartment) can be used before returning circulation to prevent pressure from building up. Gilroy 2nd ed. Fig 21.19A,B There are only 3 muscles of the flexor compartment of the arm. Gilroy 2nd ed. Fig 21.20A,C The biceps brachii muscle has 2 heads (“bi” meaning two). The short head of the biceps arises from the coracoid process and the long head arises from the supraglenoid tubercle of the scapula. Insertion is primarily on the radial tuberosity although there is a very superficial bicipital aponeurosis in the medial forearm. Since this muscle crosses two joints, the glenohumeral and the elbow joint, it functions at both joints. It is a weak flexor of the shoulder joint while it is a very powerful flexor and supinator at the elbow. Attachment point: supraglenoid tubercle (long head); coracoid process (short head) Attachment point: radial tuberosity on radius, antebrachial fascia via bicipital aponeurosis N: musculocutaneous Fx: supinates and flexes forearm Gilroy 2nd ed. Fig 21.20A,C The other muscles of the anterior compartment are the brachialis and coracobrachialis muscles. The former arises from the distal half of the anterior humerus and inserts on the ulnar tuberosity. This is also a flexor at the elbow, but a relatively weak one compared to the biceps. The coracobrachialis muscle runs from the coracoid process to the midshaft of the humerus on the medial side of the arm. Since it is on the medial and anterior side of the arm, it flexes and adducts the arm at the glenohumeral joint. Gilroy 2nd ed. Fig. 24.11A; Schuenke Vol. 1 2nd ed. Fig 17.366C The nerves of the upper extremity arise as terminal branches of the brachial plexus. The musculocutaneous (MC) nerve arises from the lateral cord of the brachial plexus and contains mainly C6 and C7 nerve fibers. The MC nerve is easily identified during dissection because it pierces (and innervates) the coracobrachialis muscle. The nerve travels in the arm between the biceps and brachialis muscles, innervates them, then emerges lateral to the biceps tendon at the elbow; here it changes “names to the lateral antebrachial cutaneous nerve, which innervates the skin of the anterolateral forearm. Gilroy 2nd ed. Fig. 24.11A; Schuenke Vol. 1 2nd ed. Fig 17.371G, 17.373G The median and ulnar nerves have no branches in the arm!! Note that the median nerve arises from contributions from both the lateral and medial cords of the brachial plexus, while the ulnar nerve comes from the medial cord alone. The median nerve passes the elbow in the company of the brachial artery. The ulnar nerve passes posterior to the medial epicondyle, where it's vulnerable to injury. At some point you have probably “hit your funny bone”. What you actually did was transiently entrap or compress your ulnar nerve against the bony structures of the elbow. Gilroy 2nd ed. Fig. 24.1B Recalll that the axillary artery becomes the brachial artery as it passes the teres major muscle. The first major branch to come off the brachial artery is the profunda brachii (or deep brachial artery) which follows the radial nerve in the radial (spiral) groove. As the brachial artery passes the elbow it divides into the radial artery that remains quite superficial, and the ulnar artery that goes deep. Note: sometimes the brachial artery divides into radial and ulnar arteries within the flexor compartment of the arm. More commonly, this division occurs in the forearm. Gilroy 2nd ed. Fig. 24.35 An important relationship to keep in mind is the neurovascular bundle located between the flexor and extensor muscles on the medial side of the arm. The median and ulnar nerves, and brachial artery are in close proximity here. This is where the brachial pulse can be palpated. Usually the radial pulse is checked first, but it is important to know how to palpate the brachial pulse too. For instance, we typically take an infant’s brachial pulse instead of the radial pulse. Schuenke Vol. 1 2nd ed. Fig. 17.357D In many places across the body, you will find a set of deep veins and superficial veins. There are deep veins that follow each of the major arteries, called venae comitantes. However, the superficial veins are somewhat different because they run independently (of arteries) in the superficial fascia (superficial veins are important in thermoregulation, since increased blood flow to the superficial veins helps radiate heat). When vigorous muscle contraction compresses the deep veins, venous blood is shunted into the superficial veins and causes them to become more prominent (like the “climber’s pump” in the image). The superficial veins also provide an excellent location to obtain blood or for intravenous access. Gilroy 2nd ed. Fig. 24.36A, 24.6 The superficial veins of the upper limb begin on the dorsum of the hand and typically continue in two groups, a lateral one called the cephalic venous system and a medial one called the basilic system (but this can/does vary). There are usually communications between these systems at the elbow, most notably a large vein from the cephalic to the basilic called the median cubital vein. Any one of these veins can be accessed at the elbow to obtain blood. Theime Anatomy: An Essential Textbook 2nd ed. Fig 14.14A The triangular shaped area marked by an imaginary line through the epicondyles and by the borders of the pronator teres muscle and brachioradialis muscles, is called the cubital fossa. The cubital fossa has superficial veins as well as some cutaneous nerves. The biceps tendon and bicipital aponeurosis are in this region. It's important to understand this area since directly beneath the bicipital aponeurosis are larger nerves and the brachial artery. These can be accessed or damaged in this region by deeper penetrations. Gilroy 2nd ed. Fig. 24.36C The median nerve and brachial artery are the most likely structures to be damaged by penetrations in this area. From lateral to medial the order of structures is biceps tendon, brachial artery, and median nerve (mnemonic = T A N).