Trail Guide Shoulder OIAs

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San Diego State University *

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Anatomy

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Oct 30, 2023

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S EEE R REREREREERREEERENEREEERRERRERNERENRRRRRERARRORAEE Deltoid The triangle-shaped deltoid is located on the cap of the shoulder. The origin of the deltoid (which is, interestingly enough, identical to the insertion of the trapezius) curves around the spine of the scapula and clavicle forming a “V" shape. From this broad origin, the Middle fibers converge down the arm to attach at the deltoid fibers tuberosity (2.36). The deltoid fibers can be divided into three segments: the anterior, middle and posterior fibers. All three groups abduct the humerus, but the anterior and posterior fibers are antagonists in both flexion/ extension and medial/lateral rotation. fibers All fibers: Abduct the shoulder (glenohumeral joint) Anterior fibers: 2.36 Lateral view of deltoid Flex the shoulder (G/H joint) showing the three segments Medially rotate the shoulder (G/H joint) When Do You Use Your Deltoid? - Virtually all movements that involve the shoulder - Slipping your arms into ajacket | « Raking, shoveling, sawing m « Rowing a dinghy Horizontally adduct the shoulder (G/H joint) Posterior fibers: Extend the shoulder (G/H joint) Laterally rotate the shoulder (G/H joint) Horizontally abduct the shoulder (G/H joint) /:\. '\\\ o gy L { A 3] Lateral one-third of clavicle, acromion L,\ ™~ § and spine of scapula o} y i 2.37 Origin and Sl insertion of deltoid Deltoid tuberosity Axillary C5, 6 @ Belly of the deltoid 1) Seated. Locate the spine of the scapula, the acromion and the lateral one-third of the clavicle. Note the “V” shape these landmarks form. 2) Locate the deltoid tuberosity. 3) Palpate between these landmarks to isolate the superficial, convergent fibers of the deltoid. Be sure to explore the deltoid’s most anterior and posterior aspects. Are the fibers you feel superficial and do they 2L converge toward the deltoid tuberosity? If your s partner alternately abducts and releases, do you feel / - D the fibers contract and relax (2.38)? ' 2.38 Anterior/lateral view deltoid del-toid Grk. delta, capital letter D (A) in the Greek alphabet Shoulder & Arm | 67
2.39 Lateral view of right shoulder. Use both hands to sculpt out the edges of the deltoid, following them down to the tuberosity. sy @Deltoid as antagonist to itself To feel the antagonistic abilities of the deltoid's anterior and posterior fibers: 1) Shaking hands with your partner, place your other hand on the deltoid. 2) Keeping his elbow next to his side, ask your partner to medially and laterally rotate his arm against your resistance. Can you sense the anterior fibers contracting upon medial rotation and relaxing upon lateral rotation, and vice versa for the posterior fibers? Superior nuchal line of the occiput Spinous process of C-7 Middle fibers { Lower fibers £ i, \{/L ; 1% { ; \ k f ‘l . - \( Spinous process é‘ i of T-12 Lf | O 2.40 Posterior view of trapezius 68 | Trail Guide to the Body Trapezius | The trapezius lies superficially along the upper back and neck. Its broad, thin fibers blanket the shoulders, attaching to the occiput (the bone at the base of the head, p. 231), lateral clavicle, scapula and spinous processes of the thoracic vertebrae (2.40, 2.42). The trapezius fibers can be divided into three groups: upper (descending) fibers, middle fibers and lower (ascending) fibers. The upper and lower fibers are antagonists in elevation and depression of the scapula, respectively. All fibers of the trapezius are easy to palpate. 2.47 Origin and insertion of trapezius
’D"",””,,WU’OJ,\L'\'V-’_ Upper fibers: Bilaterally Extend the head and neck Unilaterally Laterally flex the head and neck to the same side External occipital protruberance Rotate the head and neck to the opposite side Elevate the scapula (scapulothoracic joint) Acromion Upwardly rotate the scapula (S/T joint) Middle fibers: Adduct the scapula (S/T joint) Stabilize the scapula (S/T joint) Lower fibers: Depress the scapula (S/T joint) Upwardly rotate the scapula (S/T joint) External occipital protuberance, medial portion of superior nuchal line of the occiput, ligamentum 2.42 Lateral view nuchae and spinous processes of C-7 through T-12 of trapezius Lateral one-third of clavicle, acromion and spine of the scapula Spinal portion of cranial nerve XI (accessory) and ventral ramus C2, 3, 4 () Upper fibers of the trapezius 1) Prone. These fibers form the easily accessible flap of muscle lying across the top of the shoulder. Along the posterior neck they are surprisingly skinny, each being only an inch wide. 2) Grasp the superficial tissue on the top of the Yv p shouder and feel the upper trapezius fibers. Take \ t L note of their slender quality (2.43). % T s 3) Follow the fibers superiorly toward the base of the S il head at the occiput. To feel the fibers along the posterior neck contract, stand at the side of the table m and ask your partner to extend his head “a quarter inch off the face cradle” Then follow the fibers inferiorly to the lateral clavicle. == s the muscle you are grasping thin and superficial? 2N Grasp the fibers along the top of the shoulder and have your partner elevate his scapula gently toward his ear. Do the muscle fibers become taut? As your partner extends his head, you will likely see two parallel “speed bumps” running along the posterior neck. These bulges are formed primarily by the deeper semispinalis capitis muscle (p. 201), with the trapezius muscles draped on top. trapezius tra-pee-ze-us Grk. alittle table or trapezoid shape nuchae nu-kay L. nape of neck Shoulder & Arm | 69 occiput ok-si-put L. the back of the skull
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RN NS ... et A/‘K g‘; ] b \ Latissimus Dorsi and Teres Major The latissimus dorsi is the broadest muscle of the back. Its thin, superficial fibers originate at the low back, ascend the side of the trunk and merge into a thick bundle at the axilla (2.46). Both ends of the latissimus dorsi are difficult to isolate; however, its middle portion next to the lateral border of the scapula is easy to grasp. The teres major is called “lat’s little helper” because it is a complete synergist with the latissimus dorsi (2.47). It is superficial and located along the scapula’s lateral border between the latissimus dorsi and teres minor. Although they share names, the teres major and teres minor rotate the arm in opposite directions—the major medially, the minor laterally. The latissimus dorsi and teres major are sometimes called the “handcuff muscles;’ since their actions collectively bring the arms into the “arresting” position! Latissimus Dorsi Extend the shoulder (glenohumeral joint) Adduct the shoulder (G/H joint) Medially rotate the shoulder (G/H joint) Inferior angle of scapula, spinous processes of last six thoracic vertebrae, last three or four ribs, thoracolumbar aponeurosis and posterior iliac crest n Intertubercular groove of the humerus Thoracodorsal C6,7, 8 Teres Major Extend the shoulder (glenohumeral joint) Adduct the shoulder (G/H joint) Medially rotate the shoulder (G/H joint) Inferior angle and lower one-third of lateral border of the scapula n Crest of the lesser tubercle of the humerus Lower subscapular C5, 6, 7 latissimus dorsi la-tis-i-mus dor-si L. widest of the back teres teh-reez Thoracolumbar aponeurosis Posterior iliac crest 2.46 Lateral/posterior view of latissimus dorsi 2.47 Posterior view of teres major The latissimus dorsi not only moves the arm, but, because of its broad origin, can also affect the trunk and spine. Contraction of the left latissimus dorsi assists in lateral flexion of the trunk to the left. If the arm is fixed, as when hanging from a bar, the latissimus will assist in extension of the spine and tilting of the pelvis anteriorly and laterally. L. rounded, finely shaped Shoulder & Arm | 71
F ) F e ) ) n ) = () [ " = [ e [ = [ ) = e L - = L) =) = - - @ = Supraspinatus Abduct the shoulder (glenohumeral joint) Stabilize the head of humerus in glenoid cavity Supraspinous fossa of the scapula n Greater tubercle of the humerus Suprascapular C4, 5, 6 Infraspinatus Laterally rotate the shoulder (glenohumeral joint) Adduct the shoulder (G/H joint) Stabilize the head of humerus in glenoid cavity Infraspinous fossa of the scapula n Greater tubercle of the humerus Suprascapular C(4), 5, 6 Teres Minor Laterally rotate the shoulder (glenohumeral joint) Adduct the shoulder (G/H joint) Stabilize the head of humerus in glenoid cavity m Upper two-thirds of lateral border of the scapula n Greater tubercle of the humerus Axillary C5, 6 Subscapularis Medially rotate the shoulder (glenohumeral joint) Stabilize the head of humerus in glenoid cavity Subscapular fossa of the scapula Lesser tubercle of the humerus 1] Upper and lower subscapular C5, 6, 7 2.57 Posterior view of right shoulder showing origins and insertions of supraspinatus, infraspinatus and teres minor 2.58 Anterior view of right shoulder showing origin and insertion of subscapularis Shoulder & Arm | 75
Spinous process of T-2 Rhomboid Major and Minor The rhomboid muscles are located between the scapula and vertebral column. Named for their geo- metric shape, the major (2.72) is larger than the minor (2.73). The muscles are difficult to distinguish individually. They have thin fibers that lie deep to the trapezius and superficial to the erector spinae muscles (p. 196). Spinous process of C-7 m Adduct the scapula (scapulothoracic joint) Elevate the scapula (S/T joint) Downwardly rotate the scapula (S/T joint) (3] Major: Spinous processes of T-2 to T-5 Minor: Spinous processes of C-7 and T-1 0 Mmajor: Medial border of the scapula between the spine of the scapula and inferior angle Minor: Upper portion of medial border of the scapula, across from spine of the scapula Dorsal scapular C4, 5 2.74 Posterior view of right shoulder showing origins and insertions of rhomboids 82 | Trail Guide to the Body Here is a wonderful opportunity to explore the different layers of muscle tissue between the medial border of the scapula and spinous processes of the thoracic vertebrae. The superficial trapezius, intermediate rhomboids and deep erector spinae muscles all have different fiber directions. Palpate in this area to see whether you can differentiate the perpendicular fibers of the trapezius from those of the rhomboids. Also try differentiating between the diagonal rhomboid fibers and the vertical fibers I of the erector spinae. s fwi) > with ahliae analec and Anh/ rhomboid rom-boyd Grk. in geometry, a parallelogram s
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Levator Scapula w = = | A & ¢ : ) Unilaterally: 2 Trapezius % y i P 5‘“\ f Elevate the scapula (scapulothoracic joint) > P \ E . " | ::’: : VALY Downwardly rotate the scapula (S/T joint) Splenius capitis 1 A | !; /AL \ Laterally flex the head and neck A \ Levator scapula \FE. /8 \ Rotate the head and neck to the same side M P ) (7 Bilaterally: Posterior scalene ’\i_, / 4 Extend the head and neck Transverse processes of first through fourth W cervical vertebrae Middle scalene Omohyoid Medial border of scapula, between superior 2.77 Lateral view angle and superior portion of spine of scapula Cervical 3, 4, and dorsal scapular C4, 5 When Do You Use Your Levator? + Rotating head when changing lanes in traffic + Holding a phone between your ear and shoulder « Lying on your side, snugaling your head into your pillow g e 2.78 Origin and insertion of levator scapula 1) Prone, supine or side lying. Palpating through the trapezius, locate the superior angle of the scapula (p. 53) and the upper region of the medial border. 2) Place your fingers just off the superior angle and firmly strum across the belly of the levator. The fibers will likely have a ropy texture (2.79). 3) Follow these fibers superiorly as they extend to the lateral side of the neck to the transverse processes of the cervical vertebrae (p. 180). 7 Can you differentiate the levator fibers from the 4 trapezius fibers? Do the fibers Yyou are palpating lead toward the lateral side of the neck? Trapezius 2.79 Partner prone 84 | Trail Guide to the Body 808 & Ra
the scapula Muscle fibers // underneath 2.82 Lateral view of serratus anterior 2.83 Origin and insertion of serratus anterior i 86 | Trail Guide to the Body 2.84 Anterior view with serratus highlighted Serratus Anterior Always well-developed on superheroes, the serratus anterior lies along the posterior and lateral rib cage. Its oblique fibers extend from the ribs underneath the scapula and attach to its medial border (2.82). Most of the serratus anterior is deep to the scapula, latissimus dorsi or pectoralis major; however, the portion of the serratus below the axilla (armpit) is superficial and easily accessible (2.84). This muscle is unique in its ability to abduct the scapula, making it an antagonist to the rhomboids. Palpating along the sides of the ribs can tickle, so use slow, firm pressure. Also, if you are accessing the right serratus, it may be easier to stand on the left side of the table. With the origin fixed: Abduct the scapula (scapulothoracic joint) Upwardly rotate the scapula (S/T joint) Depress the scapula (S/T joint) Hold the medial border of the scapula against the rib cage With the scapula fixed: May act to elevate the thorax during forced inhalation External surfaces of upper eight or nine ribs n Anterior surface of medial border of the scapula Long thoracic C5, 6,7, 8 Pectoralis major Serratus anterior External oblique serratus ser-a-tus L. notched 212122292299 992992999229292 AR AAAARAAANCOES
Pectoralis Major The pectoralis major is a broad, powerful muscle located on the chest. Except for the part beneath breast tissue, its convergent, superficial fibers are accessible. Pectoralis major is divided into three segments: the clavicular, sternal and costal fibers (2.88). The upper and lower fibers perform opposing actions at the shoulder joint—flexion and extension, respectively—making this muscle an antagonist to itself. All fibers: Adduct the shoulder (glenohumeral joint) Medially rotate the shoulder (G/H joint) Assist to elevate the thorax during forced inhalation (with the arm fixed) Upper fibers: Flex the shoulder (G/H joint) Horizontally adduct the shoulder (G/H joint) Lower fibers: Extend the shoulder (G/H joint) [%) Medial half of clavicle, sternum and cartilage of first through sixth ribs n Crest of greater tubercle of humerus Upper fibers: Lateral pectoral C5, 6, 7 Lower fibers: Lateral and medial pectoral C6, 7,8, T1 The difference between the white and dark meat of a cooked bird is due to its different intramuscular connective tissues. Dark and white meat are present in all mammals, but are more distinct in birds. The reason is that light-colored musculature is rich in muscle fibers and poor in sarcoplasm—the tissue that surrounds the muscle fiber— while dark meat has the exact opposite composition. And if you are fond of the “breast,” chew on this fact: a bird’s pectoralis majors make up 20-35% of its body weight. pectoralis pek-to-ra-lis L. chest Clavicular | 7 7 % Costal 2.88 Anterior view identifying the three segments of pectoralis major 2.89 Origin and insertion of pectoralis major Shoulder & Arm | 89
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2.93 Anterior view of pectoralis minor 2.94 Origin and insertion of, pectoralis minor 2.95 Brochid e o ————— 2.95 Brachial plexus, axillary artery and vein passing beneath pectoralis minor 92 | Trail Guide to the Body Pectoralis Minor The pectoralis minor lies next to the rib cage deep to the pectoralis major (2.93). lIts fibers run perpendicular to the pectoralis major fibers from the scapula’s cora- coid process to the upper ribs. During aerobic activity the pectoralis minor helps to elevate the rib cage for inhalation, The major vessels serving the arm— the brachial plexus, axillary artery and vein—cross underneath the pectoralis minor, creating the potential for neurovascular compression by this muscle (2.95). Access to the minor can be achieved by either pressing through or sliding underneath the thick pectoralis major. The second method is more specific and will be outlined here, The pectoralis minor can be sensitive, so palpate slowly, allowing your fingers or thumb to sink into the tissue, Depress the scapula (scapulothoracic joint) Abduct the scapula (/T joint) Downwardly rotate the scapula (/T joint) With the scapula fixed: Assist to elevate the thorax during forced inhalation Third, fourth and fifth ribs n Medial surface of coracoid process of the scapula ] Medial pectoral, with fibers from a communicating branch of the lateral pectoral C(6),7,8,T1 it efaacecer
Coracobrachialis The coracobrachialis is a small, tubular muscle located in the axilla (2.109). Sometimes known as the “armpit” muscle, it is a secondary flexor and adductor of the shoulder. In anatomical position, the coracobrachialis is deep to the pectoralis major and anterior deltoid and lies anterior to the axillary artery and brachial plexus. Abducting the shoulder (opening up the axilla) brings the belly of the coracobrachialis to a superficial and palpable position. Flex the shoulder (glenohumeral joint) Adduct the shoulder (G/H joint) Coracoid process of the scapula B Medial surface of mid-humeral shaft Musculocutaneous C6, 7 1) Supine. Laterally rotate and abduct the shoulder to 45°. Locate the fibers of the pectoralis major. This tissue forms the axilla’s anterior wall and will be a reference point for locating coracobrachialis. 2) Lay one hand along the medial side of the arm and move your fingerpads into the armpit. 3) Have your partner horizontally adduct gently against your resistance (2.111). Isolate the solid edge of the pectoralis major then slide off the pectoralis major fibers posteriorly (into the axilla) and explore for the slender, contracting belly of the coracobrachialis. Its belly may be visible upon adduction. . Is the muscle you are palpating on the medial A1 side of the upper arm? Does its belly lie posterior to the overlying flap of the pectoralis major? Can you strum along its cylindrical belly? When Do You Use Your Coracobrachialis? « Reaching around your face to scratch your opposite ear - Weightlifting—doing a bench press - In martial arts—a forearm block in front of your chest coracobrachialis kor-a-ko-bra-kee-al-is Coracoid process 2.110 Origin and insertion of coracobrachialis 2.111 Partner supine, palpating coraco- brachialis as your partner horizontally adducts against your resistance Shoulder & Arm | 99
Biceps Brachii The biceps brachii lies superficially on the anterior arm. It has a long head and a short head which merge to form a long, oval belly. The tendon of the long head passes through the intertubercular groove of the humerus (p. 60). This groove helps to stabilize the tendon as it rises over the top of the shoulder (2.100). The distal tendon of the biceps dives into the antecubital space (inner elbow) to attach at the radius, allowing this muscle to be the primary muscle of fore- arm supination. The majority of the biceps brachii is easily palpable. Flex the elbow (humeroulnar joint) Supinate the forearm (radioulnar joints) Flex the shoulder (glenohumeral joint) Short head: Coracoid process of scapula Long head: Supraglenoid tubercle of scapula Tuberosity of the radius and aponeurosis of the biceps brachii Musculocutaneous C5, 6 1) Supine or seated. Bend the elbow and shake hands with your partner. 2) Ask your partner to flex his elbow against your resistance. Palpate the anterior surface of the arm and locate the hard, round belly of the biceps (2.102). 3) Follow the belly distally to the inner elbow. Note how the muscle belly thins, becoming a solid, distinct tendon. Then follow the biceps proximally to where it tucks beneath the anterior fibers of the deltoid. Ask your partner to flex his elbow and see if you can L0 sculpt out the biceps’ distal tendon and distinguish it from the deeper brachialis muscle (p. 132). Also, shake hands with your partner and ask him to alternately pronate and supinate his forearm against your resistance. Do you feel the muscle belly and tendon contract upon supination? In addition to a long head and a short head, the biceps may have a head which attaches to the humerus. Reported in less than 10% of the population, this extra head originates along the medial humerus next to the coracobrachialis before joining the short head. biceps brachii bi-seps bray-key-i L. two-headed muscle of the arm Supraglenoid tubercle Coracoid process Intertubercular groove (deep) Short head Long head > 2.100 Anterior view of biceps brachii Aay | \%\ Bicipital aponeurosis 2.101 Origin and insertion of biceps brachii 2.102 Feeling biceps contract as your partner tries to flex his elbow Shoulder & Arm | 95
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Triceps Brachii The triceps brachii is the only muscle located on the posterior arm. Creating extension at the elbow and shoulder, it is an antagonist at both these joints to the biceps brachii. The triceps has three heads: long, lateral and medial (2.104, 2.105). The long head extends off the infraglenoid tubercle of the scapula (p. 54), weaving between the teres major and minor. The lateral head lies superficially beside the deltoid while the medial head lies mostly underneath the long head. All three heads converge into a thick, distal tendon proximal to the elbow. Aside from its proximal portion, which is deep to the deltoid, the triceps is superficial and easily accessible. Medial head Lateral head Medial head Olecranon of triceps brachii process When Do You Use Your Triceps Brachii? + Slamming the trunk of a car + Pounding in large nails with a big ol hammer « Raising your body during the up phase of a push-up « Dribbling a basketball triceps brachii tri-seps bray-key-i 2.104 Posterior view 2.106 Origin and insertion of triceps brachii L. three-headed muscle of the arm I3 Allheads: Extend the elbow (humeroulnar joint) Long head: Extend the shoulder (glenohumeral joint) Adduct the shoulder (G/H joint) [8 Long head: Infraglenoid tubercle of the scapula Lateral head: Posterior surface of proximal half of the humerus Medial head: Posterior surface of distal half of the humerus Olecranon process of the ulna Radial C6, 7,8, T1 Medialhead\:f[!.‘,‘\..“. \\ (il 2.105 Posterior view of the medial head of triceps brachii, deep to the lateral and long heads Shoulder & Arm | 97

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