8 Scapular Region and Arm
Scapular Region and Arm
Learning Objectives
By the end of the course students will be able to:
- Identify the muscles of the scapular and deltoid regions, their function, nerve, and blood supply
- Illustrate or describe the brachial plexus in these regions, including its parts, the nerves arising from it, their specific origins, and areas of distribution.
- Predict the functional and cutaneous loss that might result in the back, posterior shoulder, or cutaneous upper limb, given an injury to a specific site in the brachial plexus.
- Predict the injury location, given a functional or cutaneous loss in the back, posterior shoulder, pectoral region, or cutaneous upper limb.
5. Identify prominent bony features of the humerus, cubital fossa, scapula, radius, and ulna as stated in the lab manual.
Reference: Moore, Clinically Oriented Anatomy, chapter 6
Particularly Relevant Blue Boxes in Moore:
● Injury to Axillary nerve p. 710-711
● Rotator Cuff Injuries p. 712
To access the Netter Presenter Database click here
To access the Primal Pictures software click here
Check out the Primal Pictures model of the Pectoral Region and Axilla
To check of Gray’s Photographic Dissector on the Scapular Region click here
SCAPULAR AND DELTOID REGIONS (Moore 697-712)
The shoulder is composed of a group of bones and muscles that attaches the humerus to the body and allows for the great mobility of the upper limb. The two bones of the shoulder girdle are the SCAPULA and the CLAVICLE. The clavicle is a rather nondescript bone that acts as a strut, providing structural support to the shoulder girdle. The scapula has several important features, which include: the coracoid process, acromion, spine, and glenoid fossa (Netter 405, 406).
Articulations of the Shoulder Girdle
The clavicle articulates with the manubrium of the sternum forming the sternoclavicular joint (Netter 404). This joint allows elevation/depression, protraction/retraction and circumduction. The fibrous joint capsule is supported by anterior and posterior sternoclavicular ligaments and the costoclavicular ligament which runs between the clavicle and the first rib. The only bony connection of the upper limb to the trunk occurs at the sternoclavicular joint. This attachment, along with the extremely mobilescapula, allows for a wide range of movement at the shoulder girdle.
The acromioclavicular joint, (Netter 408) involving an articulation between the acromion and the clavicle is a sliding articulation with two degrees of freedom. Rotation of the scapula occurs primarily at the joint about an anterior-posterior axis. Other movements of this joint are mainly accomodations to motions that occur at the sternoclavicular joint.
The articular capsule is reinforced by strong ligaments. The coracoclavicular ligament runs from the coracoid process of the scapula to the clavicle. It is subdivided into a conoid ligament and a trapezoid ligament, both of which provide superior-inferior stability. The acromioclavicular ligament bridges the joint and provides anterior-posterior stability.
Clinical Note:
Acromioclavicular subluxation, or shoulder separation, is common despite these ligamentous reinforcements. Usually the result of traumatic downward displacement of the clavicle
The Scapulothoracic Joint
No bony articulation exists between the scapula and the thoracic cage. This conceptualized pseudojoint, which lies between the subscapularis muscle and the serratus anterior muscle, appears to function as a joint, although its movement pairs actually occur at the sternoclavicular and acromioclavicular joints.
This “joint” has three degrees of freedom, which allows for considerable motion of the scapula on the posterolateral thoracic cage.
1. Protraction/retraction occurs through a vertical axis at the sternoclavicular joint so that the scapula slides anterolaterally/posteromedially on the posterior thoracic wall
2. Elevation/depression occurs through an anterior-posterior axis at the sternoclavicular joint so that the scapula slides cranially/caudally on the posterior thoracic wall.
3. Rotation occurs through an anterior-posterior axis at the acromioclavicular joint so that the scapula rotates on the posterior thoracic wall.
The Genohumeral Joint (shoulder) will be discussed later in this chapter
Muscle Function at the Shoulder Joint
A majority of the shoulder muscles either originate or insert on the scapula. Although the muscles of the shoulder all act together, we will divide them into three groups for learning purposes:
I — muscles that originate from the axial skeleton and insert onto the humerus
II — muscles that originate from the axial skeleton and insert onto the shoulder girdle
III – muscles that originate from the shoulder girdle (the scapula plus the clavicle) and insert on the humerus
Groups I and II are also known as axioappendicular muscles and Group III is also known as scapulohumeral muscles.
Group I — BODY TO HUMERUS (Axioappendicular muscles)
This group contains two muscles, the Pectoralis Major and the Latissimus Dorsi. Both muscles insert onto the anterior and proximal humerus, but originate from the anterior and posterior body wall respectively (Netter 409). The pectoralis major forms the anterior border of the axilla, while the latissimus dorsi forms the posterior border. Both of these muscles ADDUCT and MEDIALLY ROTATE the humerus. The latissimus dorsi also extends the humerus.
Group II — BODY TO SCAPULA (Netter 413) (Axioappendicular muscles)
This group contains seven muscles: the subclavius, rhomboid major, rhomboid minor, levator scapulae, pectoralis minor, serratus anterior, and trapezius.
Subclavius –This is a small and unimportant muscle found inferior to the clavicle. Its only practical function is to protect the large adjacent blood vessels in the case of a fractured clavicle.
There are three small muscles that originate from the spinous processes of vertebrae and insert onto the medial edge of the scapula: Rhomboid Major, Rhomboid Minor, and Levator Scapulae. The rhomboids contract to draw the scapula medially towards the body’s midline. The levator scapulae muscles work to elevate the scapula. Together, these muscles oppose the pull of the serratus anterior, which holds the medial edge of the scapula tightly against the ribs.
Pectoralis Minor – This muscle originates from ribs 3, 4, and 5 and inserts onto the coracoid process of the scapula. It functions in bringing the scapula forward and down. It is found immediately deep to pectoralis major muscle.
Serratus Anterior – This muscle originates from the first nine ribs anteriorly and wraps posteriorly around the lateral rib cage. As is wraps around the body wall, it passes deep to the scapula and subscapularis muscle and inserts onto the scapula’s medial edge. It works to bring the scapula forward around the body wall, thus bringing the shoulder forward.
Trapezius – This is a superficial back muscle and covers the rhomboids and levator scapulae muscles. It originates from all of the spinous processes of the cervical and thoracic vertebrae and inserts onto the spine of the scapula. The trapezius is a very large muscle with several components; depending on which portion of the muscle contracts, the scapula can be moved superiorly, medially, or inferiorly.
Group III — GIRDLE TO HUMERUS and the Rotator Cuff Muscles (Netter 411) (Scapulohumeral muscles)
There are six muscles in this group that work to move the humerus in relation to the shoulder girdle. These muscles also help to strengthen the otherwise very weak shoulder capsule.
The SUPRASPINATUS and INFRASPINATUS muscles arise from the posterior aspect of the scapula. The infraspinatus inserts onto the greater tubercle of the humerus and acts as a lateral rotator of the arm. The supraspinatus inserts onto the superior aspect of the humerus, and acts as an abductor of the arm for the first 15 degrees of abduction. The TERES MAJOR and MINOR originate from the lateral edge of the scapula. The teres major inserts anteriorly on the humerus, while the teres minor inserts posteriorly on the humerus; thus they are medial and lateral rotators of the shoulder, respectively. Both of the teres muscles also act to adduct the arm.
DELTOID – This muscle is the largest and most superficial in this group. It originates from both the clavicle and the spine of the scapula and inserts onto the lateral aspect of the humerus at the deltoid tuberosity. The deltoid serves as a powerful abductor of the arm. In addition, its anterior muscle fibers flex the arm and its posterior muscle fibers extend the arm.
SUBSCAPULARIS – This muscle originates from the most anterior surface of the scapula and inserts onto the anterior aspect of the proximal humerus. It inserts closely to the axis of the shoulder joint so its action varies with the position of the joint. When the shoulder is in anatomic position, the subscapularis medially rotates and adducts the arm.
Four of these muscles form the important structure known as the ROTATOR CUFF. The tendons of Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis all insert around the head of the humerus. Their fibers blend with the joint capsule and greatly strengthen the capsule. The four muscles combine to exert a strong medial pull on the joint and act as the major force holding the humeral head in the glenoid fossa of the scapula.
THE SHOULDER JOINT (Netter 408, 411; Moore 796-800)
The shoulder, or GLENO-HUMERAL joint, is a very mobile and rather unstable ball-and-socket joint. The head of the humerus is a very large “ball”, while the GLENOID FOSSA (or cavity) is a very flat and shallow “socket”. The glenoid fossa is slightly deepened — in an analogous fashion to the acetabulum — by the GLENOID LABRUM, a ring of fibrocartilage encircling its rim. The CAPSULE of the shoulder joint is also very lax and is poorly reinforced with ligaments. The capsule extends from the rim of the glenoid fossa to the anatomic neck of the humerus and has three thickenings: the superior, middle, and inferior glenohumeral ligaments. These ligaments do little to stabilize the joint.
In the shoulder joint, stability has been sacrificed for mobility. The only factor that prevents continual dislocation of the joint is the attachment of the rotator cuff muscles across the joint. The ROTATOR CUFF MUSCLES — supraspinatus, infraspinatus, subscapularis, and teres minor — blend with and strongly reinforce the capsule. These four muscles attach around the joint, acting to hold the humeral head in the glenoid fossa. In addition to the rotator cuff muscles, the tendon of the long head of the biceps muscle crosses and helps reinforce the joint.
Table of Muscles of Scapular Region and Shoulder (adapted from Moore’s Tables 6.4 and 6.6)
Origin Insertion Action Innervation
| trapezius | Superior nuchal line of occipital bone, nuchal ligament, spines of 7th & all thoracic vertebrae | Lateral third of clavicle, median margin of acromion, scapular spine |
Elevates shoulder, upwardly rotates scapula,retracts scapula on thoracic wall | spinal accessory n. |
| latissimus dorsi | Spinous processes of lower thoracic vertebrae, thoracolumbar fascia crest of ilium |
floor of intertubercular groove of humerus |
adducts, extends, medially rotates arm | Thoracodorsal n. |
| rhomboid major | Spinous processes of 2nd-5th thoracic vertebrae | Medial border of scapula, below root of scapular spine |
retracts and medially rotates scapula | dorsal scapular n. |
| rhomboid minor | Spine of 7th cervical and 1st thoracic vertebrae, inferior portion of nuchal ligament |
medial margin of scapula at the root of the scapular spine |
retracts and downwardly rotates scapula | dorsal scapular n. |
| levator scapulae | transverse processes of C1-C4 | medial border of scapula above root of scapular spine |
raises and downwardlyrotates scapula | dorsal scapular n. |
| supraspinatus | supraspinous fossa of scapula | superior aspect of greater tubercle of humerus |
abducts the arm(1- 15 degrees) | suprascapular n. |
| infraspinatus | infraspinous fossa of scapula | mid portion of greater tubercle of humerus |
rotates the arm laterally | suprascapular n. |
| teres minor | lateral border of scapula | lower aspect of greater tubercle of humerus | rotates arm laterally | axillary n. |
| teres major | inferior medial border of scapula | crest of lesser tubercle of humerus | adducts and rotates arm medially | lower subscapular n. |
| deltoid | lateral third of clavicle acromion process scapular spine |
deltoid tuberosity of humerus | abducts the arm(15 – 90 degrees) | axillary n. |
| triceps, long head | infraglenoid tubercle of scapula | olecranon process of ulna | extends arm and forearm | radial n. |
Note: when studying these muscles do not memorize the detailed origins and insertions of each muscle. Instead, identify the origins and insertions of these muscles on one of the skeletons in the lab and understand how each muscle operates across a particular joint.
Bursae Around the Shoulder
Several bursae lie between the various musculoskeletal components:
The subacromial bursa (Netter 408) separates the acromion process from the underlying supraspinatus muscle. The space is frequently the site of subacromial bursitis and supraspinatus tendinitis with calcium deposits. Pain associated with subacromial bursitis, felt mainly durng the initial stages of abduction and forward flexion, severely limits shoulder mobility.
The subdeltoid bursa separates the deltoid muscle from the head of the humerus and the insertions of the rotator cuff muscles. The subacromial and subdeltoid bursae frequently communicate, but neither should communicate with the joint capsule. Such a finding is an indication of a capsular tear.
Clinical Correlation
Shoulder Dislocation. Despite the multitendinous cuff and other stabilizing features, the extreme mobility of the glenohumeral joint and the shallowness of the glenoid fossa result in loss of stability, which predisposes to dislocation of the humerus. In anterior, (or, inferior), dislocations, the head of the humerus comes to lie inferior to the coracoid process. The axillary nerve is sometime injured as it lies directly below the head of the humerus in the quadrangular space (see next chapter). Dislocation stretches the anterior capsule and may avulse the glenoid labrum which increases the likelihood of recurrence. In posterior dislocations (rare) the humeral head is displaced posteriorly. Because the dislocation is away from the brachial plexus, the incidence of associated neurovascular injury is low.
COLLATERAL CIRCULATION AROUND THE SHOULDER
There are three areas of the upper limb where effective and clinically important arterial anastomoses are formed. These are the anastomoses around the SCAPULA (Netter 414), around the ELBOW (Netter 420), and in the PALM of the HAND and the DIGITS (Netter 453). In the shoulder, anastamoses occur between the circumflex branch of the subscapular artery, the posterior and anterior circumflex humeral arteries and the transverse scapular and suprascapular arteries
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Clinical Considerations: Scapular anastomosis: Surgical ligation of the subclavian-axillary artery is possible due to the extensive anastomotic connections of the scapula. In order to ligate these arteries successfully, there must be connections in the circulation both proximal and distal to the point of obstruction. The Intercostal arteries (from the descending aorta), the Suprascapular, and the Transverse Cervical arteries (from the thyrocervical trunk of the subclavian artery) all participate in the extensive anastomosis around the scapula. During a subclavian or axillary artery ligation, the normal blood flow of the Subscapular artery is reversed. This artery will begin to drain the scapular region, instead of supplying it. This allows sufficient blood to reach the distal portion of the axillary artery and to supply the remainder of the upper limb (see Blue Box 726-727). Fracture of the greater tuberosity: occurs by direct trauma or by violent contractions of the supraspinatus muscle. The bone fragment has the attachments of the supraspinatus, infraspinatus and teres minor muscles whose tendons form parts fo the rotator cuff. Fracture of the lesser tuberosity may accompany posterior dislocation of the shoulder joint and the bone fragment has the insertion of the subscapularis tendon. Fracture of the surgical neck may injure the axillary nerve and the posterior humeral circumflex artery as they pass through teh quadrangular space. Rupture of the rotator cuff may occur by a chronic wear and tear or an acute fall on the outstretched arm. A rupture of the rotator cuff, particularly with damage of the supraspinatus tendon by friction, ultimately causes degenerative inflammatory changes (degenerative tendonitis) of the rotator cuff and often to open communication between teh shoulder joint cavity and the subacromial bursa which is subject to inflammation (subacromial bursitis and supraspinatus tendonitis), resulting in a painful abduction of the arm. |
THE ARM (Moore 731-744)
The single bone of the arm is the HUMERUS (Netter 405, 406). This bone is a shaft with articular surfaces at either end. At the proximal end of the humerus there are several important structures, which include: the articular HEAD, the ANATOMICAL and SURGICAL NECKS, the GREATER and LESSER TUBERCLES, and the INTERTUBERCULAR (BICIPETAL) GROOVE (or sulcus). Along the shaft of the humerus, note the DELTOID TUBEROSITY (insertion of the deltoid muscle) and the RADIAL GROOVE posteriorly. The distal end of the humerus is noted for: MEDIAL and LATERAL EPICONDYLES, the CAPITULUM (for articulation with the radius), and the TROCHLEA (for articulation with the ulna.)
The muscles of the arm are invested within a tube of deep fascia, known as the BRACHIAL FASCIA. This fascia attaches to the LATERAL and MEDIAL INTERMUSCULAR SEPTI, to form the ANTERIOR and POSTERIOR COMPARTMENTS of the arm (Netter 421). Note that the medial intermuscular septum splits to surround the nerves and vessels, forming the neurovascular bundle.
ARM – POSTERIOR (EXTENSOR) COMPARTMENT
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The posterior compartment of the arm contains one muscle, the TRICEPS BRACHII (Netter 418). This muscle is a powerful EXTENSOR of the FOREARM. It has three heads of origin, which all insert by a common tendon into the olecranon of the ulna. LONG HEAD — originates from the infraglenoid tubercle of scapula LATERAL HEAD — originates from the proximal 1/2 of the posterior humerus (proximal and lateral to the radial groove) Deep to both the long and lateral head is the: MEDIAL HEAD — which arises from the distal 1/2 of the posterior humerus (distal to the radial groove) The RADIAL (or SPIRAL) GROOVE separates the origin of the medial and lateral heads of the triceps brachii muscle. |
The RADIAL NERVE (Netter 465) innervates all three heads of triceps brachii muscle. The nerve wraps distally and laterally around the posterior aspect of the humerus. The radial nerve runs in the radial groove, deep to the long and lateral muscle heads and immediately adjacent to the shaft of the humerus. Occasionally, a fractured humerus will transect the radial nerve, thereby paralyzing the extensor muscles of the forearm. The radial nerve crosses the elbow joint by passing deeply between the brachialis and brachioradialis muscles; the nerve lies lateral and anterior to the elbow joint. In addition, the PROFUNDA BRACHII ARTERY (a branch of the brachial artery) travels in the radial groove with the nerve to supply the triceps brachii muscle.
The MUSCULOCUTANEOUS NERVE (Netter 462) , a preaxial terminal branch of the brachial plexus, innervates all the muscles of the anterior compartment. The nerve passes directly through coracobrachialis and descends within the fascia of the arm, between the biceps brachii and brachialis muscles. The nerve emerges on the lateral border of biceps, proximal to the elbow joint, and continues distally to supply cutaneous innervation to the lateral forearm (named the lateral cutaneous nerve of the forearm). This ‘two-part’ innervation, muscular in the arm, cutaneous in the forearm, gives the nerve its name
Scapular and Deltoid Regions quiz click here