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Questions and Answers
What is the unique feature of the clavicle that contributes to shoulder elevation?
Which structures are directly involved in the articulation with the clavicle?
What is the role of the conoid tubercle and trapezoid line on the clavicle?
Which landmark is found on the posterior surface of the scapula?
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How does the thoracic cage interact with the shoulder girdle?
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What are the boundaries of the triangular interval?
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Which artery is found within the quadrangular space?
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What is the primary function of the triangle of auscultation?
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Which joint is considered the only true connection between the upper extremity and the axial skeleton?
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What types of joint surfaces are found at the sternoclavicular joint?
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What is the anatomical significance of the superior angle of the scapula?
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Which of the following correctly describes the relationship between the humerus and the glenoid fossa?
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Which structure is NOT associated with the acromion process?
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What is the primary method for stabilizing the scapula to the thoracic cage?
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In terms of anatomical landmarks, where is the intertubercular groove located on the humerus?
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Which ligament is primarily responsible for limiting superior movement of the clavicle at the SC joint?
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What is a key function of the costoclavicular ligament?
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Which movements of the clavicle are primarily associated with its function during shoulder elevation?
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What is the primary role of the trapezoid ligament in the AC joint?
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What deformity is observed in an AC joint separation when the ligaments are damaged?
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Study Notes
The Shoulder Girdle
- The shoulder girdle is comprised of the clavicle, scapula, and humerus.
- The clavicle is the only bone that forms a true articulation with the axial skeleton for the upper extremity.
- The scapula is crucial for shoulder movement, providing mobility and stability.
- The clavicle has two convexities: one anterior, from the sternoclavicular (SC) joint, and one posterior, approaching the acromioclavicular (AC) joint.
- The clavicle is thicker at the sternal end and flatter at the acromial end.
- On the inferior surface of the clavicle, near the acromial end, there are two landmarks: the conoid tubercle and the trapezoid line.
- The conoid tubercle and the trapezoid line are attachment points for the conoid ligament and trapezoid ligament, respectively.
Scapular Landmarks
- The scapular spine is located on the posterior surface of the scapula.
- The superior angle of the scapula sits at the level of vertebrae T2.
- The scapular spine sits at the level of T3.
- The inferior angle of the scapula sits at the level of T7.
- The supraspinous fossa and infraspinous fossa are located on the posterior side of the scapula.
- The coracoid process extends anteriorly from the scapula.
- The acromion process is a flat shelf on the scapula.
- The glenoid fossa is located on the lateral side of the scapula, where the head of the humerus sits.
- The superior glenoid tubercle and the inferior glenoid tubercle are located above and below the glenoid fossa.
Humerus
- The head of the humerus articulates with the glenoid fossa to form the glenohumeral joint.
- The anatomical neck is the true neck of the humerus.
- The surgical neck is a common fracture location.
- The lesser tuberosity points anteriorly.
- The greater tuberosity is located laterally.
- The intertubercular groove is located between the lesser and greater tuberosities.
Key Spaces of the Shoulder
- The triangular space is bounded by teres minor, teres major, and the long head of triceps.
- The circumflex scapular artery runs through the triangular space.
- The triangular interval is bounded by the long head of triceps, teres major, and the lateral head of triceps.
- The radial nerve and profunda (deep) brachial artery run through the triangular interval.
- The quadrangular space is bordered by teres minor, the long head of triceps, teres major, and the shaft of the humerus.
- The axillary nerve and posterior circumflex humeral artery run through the quadrangular space.
- The triangle of auscultation is located on the posterior aspect of the shoulder, and is bounded by trapezius, latissimus dorsi, and rhomboid major.
- This space allows for easier access to lung sounds during auscultation.
- The clavipectoral triangle is bounded by pectoralis major, clavicle, and deltoid.
- The coracoid process can be palpated within this space.
Sternoclavicular (SC) Joint
- The SC joint is a saddle joint that connects the clavicle to the sternum.
- It functions similar to a ball and socket joint.
- An articular disc made of fibrocartilage divides the SC joint into two cavities.
- The SC joint is reinforced by strong ligaments: anterior SC ligament, interclavicular ligament, and costoclavicular ligament.
- The SC joint allows for elevation, depression, posterior rotation, anterior rotation, protraction, and retraction of the clavicle.
- Movement at the SC joint is crucial for the movement of the scapula and clavicle, ultimately affecting shoulder movement.
Acromioclavicular (AC) Joint
- The AC joint connects the distal end of the clavicle to the acromion process of the scapula.
- It is classified as a synovial planar joint, though it may also be considered a syndesmosis.
- The AC joint is stabilized by the acromioclavicular ligament, which is the joint capsule, and the coracoclavicular ligaments (trapezoid and conoid ligaments).
- The coracoclavicular ligaments are crucial in preventing the scapula from being pulled down and away from the clavicle.
- The AC joint is more commonly injured than the SC joint (separation).
Acromioclavicular (AC) Joint
- The AC joint is a gliding plane joint with limited motion
- It is stabilized by the acromioclavicular ligament and coracoclavicular ligament (conoid and trapezoid ligaments)
- The coracoacromial ligament is not part of the AC joint but helps create a roof for the glenohumeral joint
Movement of the AC Joint
- No muscles directly move the AC joint
- Movement of the scapula will translate to movement of the AC joint
- Muscles that create scapular movement (e.g., upper trapezius, pectoralis minor) will result in gliding motion of the AC joint
Glenohumeral Joint
- The glenohumeral joint is a true ball-and-socket joint
- The glenoid fossa is shallow, making the joint inherently unstable
- The glenohumeral joint relies heavily on ligaments and muscles for support
Glenohumeral Joint: Ligaments
- The glenohumeral joint capsule has significant laxity, especially inferiorly
- The joint capsule is thickened by the superior, middle, and inferior glenohumeral ligaments
- The coracohumeral ligament contributes to thickening the anterior capsule
- The coracoacromial ligament forms the coracoacromial arch
- The coracoacromial arch forms a roof over the glenohumeral joint
Glenohumeral Joint: Bursa
- The subacromial-subdeltoid bursa lies between the supraspinatus tendon and the acromial arch
- The subscapularis bursa communicates with the joint capsule
Scapulothoracic Joint
- The scapulothoracic joint is a functional relationship between the scapula and the thoracic cage
- Movement of the scapula on the thoracic cage is stabilized by the muscles that attach to the scapula
- The scapulothoracic joint does not have a joint classification
Scapulothoracic Joint: Movement
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The scapula can exhibit protraction, retraction, upward rotation, downward rotation, elevation, and depression
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Upward rotation of the scapula is crucial for reaching overhead
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The scapula contributes 60 degrees of motion during overhead reaching
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The glenohumeral joint contributes 120 degrees of motion during overhead reaching ### Shoulder Girdle Muscles: Posterior
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Trapezius originates from the ligamentum nuchae (supraspinous ligament of the cervical region), the C7 spinous process, and the T1-T12 spinous processes.
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Trapezius inserts on the lateral third of the clavicle, the acromion, and the scapular spine.
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Trapezius is a key player in upward scapular rotation, with superior fibers contributing to scapular elevation and inferior fibers contributing to scapular depression.
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Trapezius is innervated by the spinal accessory nerve (cranial nerve XI).
### Shoulder Girdle Muscles: Posterior (cont.)
- Latissimus Dorsi originates from the T7-T12 spinous processes, the thoracolumbar fascia, and indirectly from the iliac crest.
- Latissimus Dorsi inserts on the floor of the intertubercular groove on the humerus.
- Latissimus Dorsi acts as a shoulder extensor, adductor, and medial rotator.
- Latissimus Dorsi is innervated by the thoracodorsal nerve (C6-C8 nerve roots).
### Shoulder Girdle Muscles: Posterior (cont.)
- Levator Scapulae originates from the transverse processes of the C1-C4 vertebrae.
- Levator Scapulae inserts on the superior medial border of the scapula.
- Levator Scapulae acts as a downward rotator and, like the trapezius, can contribute to scapular elevation.
- Levator Scapulae is innervated by the dorsal scapular nerve (C4-C5 nerve roots).
### Shoulder Girdle Muscles: Posterior (cont.)
- Rhomboid Major and Minor share a common function and origin. They originate from the C7-T5 spinous processes.
- Rhomboid Major and Minor insert on the medial border of the scapula (from superior to inferior angle).
- Rhomboid Major and Minor act to retract the scapula toward the spine and to downward rotate the scapula.
- Rhomboid Major and Minor are innervated by the dorsal scapular nerve (C4-C5 nerve roots).
Shoulder Girdle Muscles: Anterior
- Pectoralis Major has two components: a clavicular head that attaches to the medial aspect of the clavicle, and a sternal head attaching to the sternum and costal cartilage of the first six ribs (with a slight attachment to the oblique abdominis).
- Pectoralis Major inserts on the lateral lip of the intertubercular groove.
- Pectoralis Major acts as a medial rotator, adductor, and can flex or extend the arm depending on its starting position.
- Pectoralis Major is innervated by the lateral and medial pectoral nerves (C5-T1) and is significantly impacted by C6 injuries.
Shoulder Girdle Muscles: Anterior (cont.)
- Pectoralis Minor originates from ribs 3-5.
- Pectoralis Minor inserts on the coracoid process of the scapula.
- Pectoralis Minor is a scapular stabilizer, pulling the coracoid process anterior and inferiorly, which can cause anterior tipping of the scapula.
- Pectoralis Minor is innervated by the medial pectoral nerve (C8-T1).
Shoulder Girdle Muscles: Anterior (cont.)
- Subclavius is a small muscle located beneath the clavicle. Its innervation is the nerve to the subclavius.
Shoulder Girdle Muscles: Anterior (cont.)
- Serratus Anterior is a very important muscle that originates from the lateral aspects of ribs 1-8 and wraps under the scapula to insert on the medial border of the scapula.
- Serratus Anterior acts as a stabilizer and an upward rotator of the scapula. A weak serratus anterior can lead to scapular winging.
- Serratus Anterior is innervated by the long thoracic nerve (C5-C7) and is crucial for overhead reaching.
Pectoral and Anterior Shoulder Girdle Fascia
- Pectoral Fascia: Encases pectoralis major and connects to the abdominal wall, axillary region, and deltoid fascia.
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Clavipectoral Fascia: A deeper layer connecting the clavicle, pectoralis minor, and axillary fascia.
- Costocoracoid Membrane: Connects the clavicle and subclavius to the superior aspect of pectoralis minor. Important for passage of nerves and vessels like the lateral pectoral nerve, cephalic vein, and thoracoacromial artery.
- Suspensory Ligament of the Axilla: Connects pectoralis minor to the axillary fascia, which is the floor of the armpit.
Intrinsic Muscles of the Shoulder Girdle
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Prime Movers: Larger, bulkier muscles responsible for the main actions of the shoulder.
- Teres Major: Originates at the inferior angle of the scapula and inserts on the medial lip of the intertubercular groove. Actions include adduction, extension, and medial rotation of the humerus. It's innervated by the lower subscapular nerve (C5, C6).
- Deltoid: Originates along the lateral one-third of the clavicle, acromion, and scapular spine, and inserts on the deltoid tuberosity of the humerus. Actions include shoulder flexion, abduction, extension, lateral rotation, and medial rotation depending on the fibers activated. Innervated by the axillary nerve (C5, C6).
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Rotator Cuff: Smaller muscles primarily involved in glenohumeral joint stability.
- Supraspinatus: Origin: Supraspinous fossa of the scapula. Insertion: Greater tuberosity of the humerus. Action: Shoulder abduction (initially) and external rotation. Innervation: Suprascapular nerve (C4, 5, 6). Most commonly torn rotator cuff muscle.
- Infraspinatus: Origin: Infraspinous fossa of the scapula. Insertion: Greater tuberosity of the humerus. Action: Shoulder external rotation and stability. Innervation: Suprascapular nerve (C4, 5, 6).
- Teres Minor: Origin: Lateral border of the scapula. Insertion: Greater tuberosity of the humerus. Action: Shoulder external rotation and stability. Innervation: Axillary nerve (C5, 6).
- Subscapularis: Origin: Subscapular fossa of the scapula. Insertion: Lesser tuberosity of the humerus. Action: Shoulder internal rotation and stability. Innervation: Upper and lower subscapular nerves.
Shoulder Joint Movements
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Scapular Rotation:
- Upward Rotators: Trapezius (upper) and serratus anterior.
- Downward Rotators: Trapezius (lower) and rhomboids.
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Humerus Rotation:
- Internal (Medial) Rotators: Pectoralis major, latissimus dorsi, teres major, subscapularis.
- External (Lateral) Rotators: Infraspinatus and teres minor.
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Note: Visualizing muscle actions by drawing or using models helps understand how origin and insertion points relate to movement.
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