Lecture 5 Shoulder

• The shoulder serves as the junction between the trunk and upper limb.
• It is subdivided into pectoral, deltoid, and scapular regions.
• The shoulder's structure prioritizes range of motion, which can compromise stability and lead to injuries.
• Support is mainly provided by extensive musculature.
• Axioappendicular muscles originate from the thorax and attach to the scapula, clavicle, or humerus.
• Scapulohumeral muscles originate from the scapula and attach to the humerus.

Pectoral Region

• It is the anterior aspect of the shoulder, overlapping the anterior thoracic wall.
• It comprises bone, muscle, and fascial planes.
• Muscles in this region are classified as anterior axioappendicular.

Clavicle

• It is a part of the pectoral girdle, connecting the axial and appendicular skeletons.
• The clavicle forms the superior margin of the pectoral region.
• It gives protection to vital neurovascular structures beneath.
• It's an "S" shaped bone that articulates with the sternum medially and anteriorly, and with the scapula laterally and posteriorly.
• Fractures cause prominent deformity, due to elevation of medial fragment due to muscle pull and sag of lateral aspect due to limb sag.
• The structural weak point is 2/3 along the mid-shaft.
• It's arguably the most commonly broken bone in the body due to curvature and differences in ossification of regions; medial 2/3 endochondral, lateral 1/3 intramembranous
• The superior surface is smooth and easily palpated through thin cutaneous tissue.
• The inferior surface is rough due to muscle/ligament attachments.
• The triangular shaped sternal head articulates with the manubrium, forming the sternoclavicular joint.
• The sternoclavicular joint is the only direct articulation between the axial and appendicular skeleton.
• The sternoclavicular joint contains an articular disc for multiplanar motions and is reinforced by strong ligaments.
• The sternoclavicular joint acts as strut; subtle movements translate into larger movements of clavicular end, increasing shoulder range of motion
• Think: boom arm of a crane
• The broad, flat lateral end articulates with the acromion process of the scapula through the acromioclavicular joint.
• The acromioclavicular joint indirectly links scapula to axial skeleton
• Minimal motions are permitted at the acromioclavicular joint, due to strong reinforcing ligaments. and visible upon X-ray
• Shoulder separation occurs when the acromion process separates from the clavicle due to ligament tearing.
• Shoulder separation should not be confused with shoulder dislocation.
• Shoulder separation has varying degrees, depending on severity, and results in point tenderness

Pectoralis Major Muscle

• It is the most superficial portion of the pectoral region.
• It has a broad origin, dividing the muscles into two heads: sternal and clavicular.
• The sternal head originates off the manubrium and body of sternum
• The clavicular head originates off the anteroinferior surface of the clavicle
• Fibers converge to insert on the lateral ridge of the bicipital groove on the humerus.
• It adducts, horizontally flexes, and medially rotates the shoulder.
• Innervation is by medial/lateral pectoral nerves off the brachial plexus.
• It is invested in pectoral fascia.

Pectoralis Minor Muscle

• It's located in the deeper part of the pectoral region.
• It has a broad origin off ribs 3-5 and fibers converging upon the coracoid process.
• It stabilizes the scapula and elevates ribs.
• Innervation is by the medial pectoral nerve off the brachial plexus.

Subclavius Muscle

• It's a slender muscle connecting the clavicle to the 1st rib.
• It anchors/depresses the clavicle during motion.
• Innervation is by the nerve to subclavius.

Clavipectoral Fascia

• It is a broad continuous sheet of fascia in the same plane as the pectoralis minor muscle.
• It is divided into subregions, depending on location
• The superior portion invests the clavicle and subclavius muscle.
• A thickening of the fascial sheet just inferior to subclavius runs from the coracoid process to the costochondral junction of the first rib and is referred to as the costocoracoid ligament.
• It thins inferior to become costocoracoid membrane
• The fascia continues inferiorly, enveloping the pectoralis minor muscle.
• A single layer projects off the lateral border of the pectoralis minor to form the suspensory ligament of the axilla.
• It is pierced by neurovascular structures projecting to the superficial pectoral region, upper limb.

Scapular Region

• It's the posterior aspect of the shoulder, overlapping with the back.
• It is primarily made up of bone and dense musculature.
• Muscles can be divided into posterior axioappendicular and scapulohumeral muscles.
• Posterior axioappendicular muscles are discussed previously with the back
• Scapulohumeral muscles are intrinsic shoulder muscles

Scapula

• It forms the bony wall of the posterior region of the shoulder.
• It's a triangular flat bone connecting the clavicle to the humerus.
• The only bony connection to the axial skeleton is indirectly through the acromioclavicular joint.
• It is mainly supported through numerous muscle attachments.
• The resting position and movement of the scapula are strong indicators of numerous muscle imbalances.
• Assessments of shoulder pain should always include assessment of resting position, movement relative to humerus through multiplanar ROM (scapulohumeral rhythm)
• The 3 borders (superior, medial, lateral) typically thicker than rest of body due to muscle pull
• The head of the scapula is found at the lateral angle, the site of the glenoid fossa.
• The glenoid fossa articulates with humerus to form shoulder joint
• The spine of the scapula is a prominent ridge on the posterior aspect for muscle attachment, dividing the surface into supraspinous and infraspinous fossae.
• The lateral end of the spine curves anteriorly, forming the acromion process for articulation with the clavicle at the acromioclavicular joint.
• The acromion forms the roof of the subacromial tunnel and the site of inflammation, pressure, supraspinatus tendinitis
• The coracoid process projects off the anterior surface and is a site of muscle attachment.

The Rotator Cuff

• A set of 4 intrinsic muscles that move the humerus relative to the scapula.
• Mnemonic SITS is used to name the muscles: Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.

Supraspinatus

• It has an extensive origin off the supraspinous fossa.
• Fibers run in parallel fashion laterally, tendon passes through subacromial tunnel to insert on the superior aspect of the greater tubercle of humerus.
• It initiates abduction of shoulder and assists with fixation of the humeral head.
• Innervation is by the suprascapular nerve.
• It is the most common muscle affected in rotator cuff tears, likely due to angle of insertion onto humerus, passage through subacromial tunnel.
• Tears can be due to acute trauma (e.g. falls) or chronic degeneration (e.g. severe tendinitis).

Infraspinatus

• It has an extensive origin along the infraspinous fossa.
• Fibers converge to insert on the middle aspect of the greater tubercle.
• It is a shoulder fixator and external rotator.
• Innervation is by the suprascapular nerve.

Teres Minor

• It's a round muscle originating off the inferior aspect of the infraspinous fossa.
• It inserts on the inferior aspect of the greater tubercle.
• Often difficult to differentiate from infraspinatus muscle
• It acts with the infraspinatus to fixate, externally rotate the shoulder.
• Innervation is by the axillary nerve.

Subscapularis

• It has an extensive origin off the subscapular fossa.
• It crosses anterior to the shoulder joint to insert on the lesser tubercle.
• It is a shoulder fixator and internal rotator.
• Innervation is by the upper/lower subscapular nerves.

Teres Major

• It's a rounded muscle similar in appearance to teres minor.
• It originates just inferior to teres minor off the inferior angle of the scapula.
• It passes anterior to the shoulder joint to insert on the medial lip of the bicipital groove, just medial to the latissimus dorsi muscle.
• It is a medial rotator of shoulder.
• Innervation is by the lower subscapular nerve.
• NOT a part of the rotator cuff (does not attach to tubercles).

Deltoid Region

• The lateral aspect of the shoulder.
• Primarily consists of bone and muscle.
• The superior margin is delineated by the bony ridge formed by the acromion process and the lateral aspect of the clavicle.
• The subacromial tunnel is the space immediately inferior to the acromial ridge.
• Permits passage of supraspinatus tendon
• It contains bursa to reduce friction during shoulder abduction.
• The bony frame prevents expansion of subacromial tunnel; inflammatory conditions (supraspinatus tendinitis, subacromial bursitis) results in increased pressure, pain in region; also results in greater wear on supraspinatus tendon, especially in full abducted position

Deltoid Muscle

• It is a strong, thick muscle responsible for the rounded nature of the shoulder.
• It has a broad origin off the lateral rim of the acromion and clavicle.
• Fibers converge on the deltoid tuberosity of the humerus.
• This convergence results in different motions, depending on fibers contracting.
• Anterior fibers flex the shoulder.
• Posterior fibers extend the shoulder.
• Intermediate fibers abduct at the shoulder.
• Anterior/posterior fibers assist with abduction (stabilizers)
• Deltoid is unable to initiate abduction from the anatomical position due to 0 mechanical advantage (provides isometric resistance to gravitational sag in this position).
• Supraspinatus and gravity are required for first 150 of abduction.
• Innervation is by the axillary nerve off of the brachial plexus.
• The axillary nerve is closely associated with head and surgical neck of humerus; dislocations, breaks can result in acute nerve damage nerve, leading to deltoid paralysis results in loss of ability to abduct shoulder past 150, flat shoulder deformity.
• Chronic injury can also result from improper use of crutches, but is generally reversible.

Glenohumeral Joint

• The true shoulder joint.
• It is the articulation between the glenoid fossa of the scapula and the humeral head.
• It is a ball and socket joint, allowing movements in all directions.
• It has a very shallow socket, compared to other ball and socket joints (e.g. hip)
• It has a large range of motion with minimal stability, but stability is increased with isometric contraction of the rotator cuff muscles.
• Shoulder dislocations are common due to instability of the joint.
• Humeral head typically dislocates anterior and inferior
• Posterior/superior dislocation less common, due to support offered by scapular spine, acromion
• Head commonly visible as bulge in armpit when arm is abducted

Muscular Boundaries and Spaces

• The shoulder encases the axilla, a space intermediate to the thorax and the upper appendage.
• The axilla represents throughway for numerous structures passing from thorax to the upper limb.
• Sub-branches supply shoulder region, think: off-ramps from the highway
• Distinct spaces exist defined by muscular boundaries.
• Permit the passage of these sub-branches (discussed later) to their destinations

Triangular Space

• Also known as the medial axillary space or superior triangular space.
• Superior border - Teres minor (subscapularis).
• Inferior border - Teres major.
• Lateral border - Long head of triceps brachii.

Quadrangular Space

• Also known as the lateral axillary space.
• Medial border - Long head of triceps brachii.
• Lateral border - Surgical neck of humerus.
• Superior border - Teres minor (subscapularis).
• Inferior border - Teres major.

Triangular Interval

• Also known as the inferior triangular space.
• Superior border - Teres major.
• Medial border - Long head of triceps brachii.
• Lateral border - Lateral head of triceps brachii.

The Breast

• The mammary gland is composed of glandular tissue embedded in adipose tissue, suspended by ligaments, and containing small arteries, nerves, and lymphatics.
• Mammary glands exist in pockets, called lobules.
• Milk, produced in lobules, drains into lactiferous ductules, which collect into lactiferous ducts.
• Approximately 4 – 18 terminal ducts drain into the nipple.
• The lactiferous sinus is just proximal to termination of duct and expresses milk in lactating woman with suckling, manual compression
• Suspensory ligaments of the breast (Cooper’s ligaments) provide support the breast tissue, anchoring the breast to the dermis.
• With time, ligaments develop laxity, resulting in sagging breasts with advanced age.
• It is separated from the pectoralis major by the retromammilary space.
• The breast is divided into quadrants for localization of tumors/cysts: superior lateral, superior medial, inferior lateral, and inferior medial.
• The superior lateral contains a superior extension, known as the axillary process.

Breast Cancer

• Carcinoma of the breast is typically adenocarcinomas arising from the epithelial tissue surrounding the lactiferous ducts.
• It can result in hard masses within the mammary tissue, noticeable upon palpation.
• Once metastasized, cancerous cells can pass into the lymphatic system.
• Disruptions in lymphatic drainage may lead to irregularities in breast tissue, noticeable upon visible inspection.

Overview of the pectoral region's anatomy, including bones, muscles, and fascial planes. Focus on the clavicle's structure and its role in connecting the axial and appendicular skeletons. Highlights the clavicle's articulation points and common fracture site.