Lab 11 Pre-Lab Exercise:
Note: If possible you should have the material from your bone box or that available in the model room with you when you use this pre-lab material.
The clavicle, commonly called the "collar bone", is a critical component of the shoulder girdle. The upper limb is indirectly attached to the axial skeleton through the clavicle. The clavicle is a strut-like bone in the shape of a shallow letter 'S' and lies transversely on the cranial end and ventral side of the rib cage. . The clavicle articulates with two bones, the sternum and the scapula. The medial end of the clavicle expands into an ovoid and articulates with the manubrium. The lateral end of the clavicle flattens craniocaudally and articulates with the acromion of the scapula. The clavicle has a synovial joint at each end. There is an articular disc at its sternoclavicular joint. At the articulation with the scapula it is bound tightly to the acromion with ligaments that cross the synovial joint. The cranial surface of the clavicle is relatively smooth. The caudal surface of the clavicle presents a conoid tubercle which is the attachment of the conoid ligament, which binds the clavicle to the coracoid process of the scapula.
- Identify the following landmarks on the clavicle:
1. sternal end
2. acromial end
3. conoid tubercle
The scapula is a spade-shaped bone comprised of a thin triangular body and a semi-ovoid cavity known as the glenoid fossa (glenoid cavity). The glenoid fossa faces lateral and slightly anterior and cranial. A bony spine runs across the dorsal surface of the scapular body and terminates in the acromion. The scapula articulates with two bones, the humerus and clavicle. The scapula does not directly contact the bony rib cage: the two structures are separated by muscle and other soft tissue.
- Identify the following landmarks on the scapula:
1. coracoid process
3. scapular spine
4. inferior angle
- Study the sternoclavicular and acromioclavicular joints on an articulated skeleton.
- Place your fingertips on your own sternoclavicular joint, and raise, lower, protract, and retract your shoulder.
Note the relatively great mobility of the sternoclavicular joint.
- Place your fingers on the spine of your scapula and the thumb of the same hand on your clavicle, and raise, lower, protract, and retract your shoulder.
The acromioclavicular joint permits only a little fore-and-aft sliding of the scapula on the clavicle. Mobility is greatly restricted by the powerful coracoclavicular ligament that passes upward from the coracoids to the clavicle. This ligament so strongly prevents the scapula from being driven medially that, if you fall on your shoulder, you are more likely to fracture your clavicle than to dislocate the acromioclavicular joint.
- Locate the following areas of major muscle attachment on a disarticulated scapula:
- the ventral subscapular fossa (for the subscapularis muscle)
- the dorsal supraspinous fossa (for the suprapinous muscle)
- the dorsal infraspinous fossa (for the infraspinatus and teres minor muscles)
The humerus is the large single bone of the upper arm. Proximally, it articulates with the glenoid fossa of the scapula forming the glenohumeral joint. The humeral head is large and globular. Just ventral to the articular surface is the lesser tubercle, where the subscapularis attaches. Lateral to the articular surface is the greater tubercle. The rotator cuff muscles of the shoulder insert on the proximal humerus.
- Examine a disarticulated humerus and identify the following:
- humeral head
- anatomical neck
- the greater tubercle where the supraspinatus, infraspinatus, and teres major insert
- the lesser tubercle where subscapularis and the more distal attachments of the rest of the latissimus group insert
- the deltoid tuberosity where the deltoid muscle inserts
- the intertubercular groove through which the tendon of the long head of biceps brachii runs on its way from the upper edge of the glenoid fossa to the radius
The distal humerus presents a number of osteological projections. Muscles which flex and extend the hand originate on the medial and lateral epicondyles of the distal humerus respectively. The trochlea and capitulum lie between the medial and lateral epicondyles. The spool-shaped trochlea is medial to the rounded capitulum. These processes comprise the distal articular surfaces where the humerus articulates with the radius and ulna.
- Examine a disarticulated humerus and identify the following:
- the lateral epicondyle from which the superficial extensors of the forearm originate
- the medial epicondyle from which the superficial flexors of the forearm originate
- the dorsal olecranon fossa
- Flex your wrist and fingers and feel the flexor muscle mass on the medial side of the elbow contract. You can extend the wrist and fingers and feel the extensor muscles contract on the lateral side of the elbow.
4. Surface anatomy of the upper limb
Tendons, muscles, and bony landmarks in the upper limb are used to locate major arteries, veins, and nerves. Asking patients to manoeuver their upper limbs in specific ways is essential for performing neurological examinations. Tendons are used to test reflexes associated with specific spinal cord segments, and nerves can become entrapped or be damaged in regions where they are related to bone or pass through confined spaces. Vessels are used clinically as points of entry into the vascular system and for taking blood pressure and pulses.
5. Bony landmarks of the shoulder and arm
Clavicles: can be felt from end to end (subcutaneous) since they produce sinuous horizontal ridges visible at the junction of the neck to the thorax. Each clavicle is “S” shaped with its medial 2/3 convex anteriorly and its lateral 1/3 concave anteriorly. The medial end is bulbous and forms the lateral aspects of the jugular notch. Palpate the acromioclavicular (with acromion of scapula) and sternoclavicular (sternum) joints.
Scapula: the medial border, inferior angle, part of the lateral border of the scapula, as well as the spine and acromion can be palpated. The inferior angle of the scapula can be felt if the arm is allowed to hang freely by the side. The superior border of the scapula is deep to soft tissue and not readily palpable. The angle of the acromion is felt at the point of junction of the lateral border of the acromion with the inferior border of the crest of the spine. This is an important landmark as the axillary nerve winds around the surgical neck of the humerus about 5 cm distal to the angle. The angle is used as the proximal point when measuring distances in the upper extremity. Finally, the coracoid process can be felt by pressing posterolaterally immediately inferior to the junction of the middle and lateral thirds of the clavicle.
Humerus: the greater tubercle project laterally below and beyond the acromion, and with the deltoid muscle, is responsible for the round contour of the shoulder. The lesser tubercle is a prominence directed forward and lying about 2-3 cm below and lateral to the tip of the coracoid process. Medial and lateral rotation of the humerus will confirm the identification of this tubercle. The bicipital (intertubercular) groove can be found between the lesser and the greater tubercles. The tendon of the long head of the biceps brachii is palpable in the groove on flexion and extension of the elbow.
6. Soft tissue of the shoulder and arm
Trapezius: is responsible for the smooth contour of the lateral side of the neck and over the superior aspect of the shoulder. It can be seen and felt throughout its entirety when the shoulder girdles are retracted against resistance; the superior part can be palpated when the shoulders are elevated against resistance.
Posterior axillary fold: is formed by the latissimus dorsi winding around the lateral border of the teres major muscle. Latissimus dorsi forms much of the muscle mass underlying the posterior axillary fold extending obliquely upward from the trunk to the arm. Teres major passes from the inferior angle of the scapula to the upper humerus and contributes to the fold laterally. Both muscles can be palpated on resisted shoulder adduction.
Pectoralis major: can be seen and felt throughout its entire extent when it is contracted against resistance as in pressing the palm together in front of the body. Clavicular fibers can be felt if the shoulder is flexed against resistance to a position midway between flexion and extension, while the sternocostal fibers can be felt if the shoulder is extended against resistance starting in a flexed position. The inferior border of the pectoralis major muscle forms the anterior axillary fold.
Deltoid: forms the muscular eminence inferior to the acromion and around the glenohumeral joint. The anterior, middle, and posterior fibers of the deltoid can be palpated. When the arm is abducted against resistance, the anterior border of the deltoid can be felt.
The clavipectoral triangle (deltopectoral triangle) is the depressed area just inferior to the lateral part of the clavicle, bounded by the clavicle superiorly, the deltoid laterally, and the clavicular head of the pectoralis major medially.
Biceps brachii: can be readily felt and seen when the elbow joint is flexed, and the forearm is supinated against resistance. The tendon should be felt in the cubital fossa along with the bicipital aponeurosis.
Corachobrachialis: forms a slight elongated swelling just posterior to the proximal half of the medial margin of the biceps brachii.
Triceps brachii: forms the soft tissue mass posterior to the humerus and the tendon inserts onto the olecranon of the ulna (see pre-lab 12). The triceps brachii can be felt by extending the elbow against resistance.
7. Visualizing the axilla and its contents
The axillary inlet, outlet, and walls of the axilla can be established using skin folds and palpable bony landmarks. Major blood vessels, nerves, and lymphatics travel between the upper limb to the trunk through the axilla.
Axillary inlet: The anterior margin is the clavicle and the lateral limit is approximately the coracoid process.
Axillary walls: The inferior margin of the anterior wall is the anterior axillary fold and the inferior margin of the posterior wall is the posterior axillary fold. The medial wall is the upper part of the serratus anterior muscle overlying the thoracic wall. The lateral wall is the humerus.
Axillary outlet: The floor of the axilla is the dome of skin between the posterior and anterior axillary folds.
The axillary artery passes just inferior to the tip of the coracoid process and courses posterior to the coracobrachialis. Then the axillary artery, axillary vein and components of the brachial plexus pass through the axilla by travelling lateral to the dome of skin that forms the floor. The neurovascular bundle can be palpated by placing a hand into this dome of skin and pressing laterally against the humerus.
The cephalic vein travels in the superficial fascia in the cleft between the deltoid muscle and the pectoralis major muscle and penetrates deep fascia in the calvipectoral (deltopectoral) triangle to join with the axillary vein.
The brachial artery, which is a continuation of the axillary artery, begins at the inferior border of the teres major muscle. It is found on the medial side of the arm in the cleft between the biceps brachii and triceps brachii muscles. The median nerve courses with this artery, whereas the ulnar nerve deviates posteriorly from the vessel in distal regions.