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• The shoulder joint is highly mobile, allowing movement in all planes
• Works in conjunction with the shoulder girdle (scapula + clavicle)
• More mobility results in less stability, which leads to a higher risk of injury

Structure & Stability

• The Glenoid fossa is shallow, which allows a wide range of motion(ROM)
• The humeral head fits loosely, increasing motion but reducing stability
• Laxity, which is loose connective tissue, allows extreme mobility but increases the risk of dislocations, subluxations, and rotator cuff impingements

Shoulder Joint Movements & Pairings

• Shoulder movements are paired with scapular (shoulder girdle) movements
• Abduction of the shoulder pairs with upward rotation of the scapula
• Internal/External rotation involves abduction/adduction of the scapula

Planes of Motion

• Sagittal Plane movements include Flexion and Extension
• Frontal Plane movements include Abduction and Adduction
• Horizontal Plane movements include Horizontal abduction and adduction
• Transverse Plane movements include Internal and External rotation

Key Bony Landmarks - Scapula

• Glenoid fossa is a shallow socket for the humeral head
• Acromion process connects to the clavicle (AC joint)
• Coracoid process is an anterior projection and attaches to the Pectoralis minor
• Scapular spine is a posterior ridge that separates supraspinous and infraspinous fossae
• Supraspinous fossa is above the spine and is the Supraspinatus origin
• Infraspinous fossa is below the spine and is the Infraspinatus origin
• Subscapular fossa is an anterior depression and is the Subscapularis origin
• Inferior angle is a key landmark for scapular movement
• Lateral/Medial borders are sites for muscle attachment

Key Bony Landmarks - Humerus

• Humeral head articulates with the glenoid fossa
• Greater/Lesser tubercles are muscle attachment sites
• Intertubercular (Bicipital) groove is a pathway for the biceps tendon
• Deltoid tuberosity is the Deltoid muscle insertion point

Key Takeaways

• Shoulder joint movement is dependent on scapular movement
• Understanding muscle origins/insertions is crucial for movement analysis
• High mobility leads to common injuries like dislocations and impingements

Glenohumeral Joint Structure & Stability

• Glenohumeral joint describes where the Humeral head meets the glenoid fossa

• Ligaments provide primary stability (anterior & inferior) while allowing flexibility

• Superior glenohumeral ligament provides stability

• Inferior glenohumeral ligament provides stability

• Coracohumeral ligament provides stability

• Glenoid labrum is a cartilage ring that enhances stability

• Tendons surround ligaments and support movement, examples include the supraspinatus, infraspinatus, and teres minor

• Scapular tracking is key to prevent the Impingement of tendons under the acromion

Movements of the Glenohumeral Joint - Frontal Plane

• Abduction describes a lateral upward movement of the humerus that requires scapular upward rotation & elevation to avoid impingement
• Adduction describes a medial downward movement that is paired with scapular downward rotation, and can occur without crossing the midline

Movements of the Glenohumeral Joint - Sagittal Plane

• Flexion describes when the Humerus moves anteriorly and is paired with scapular upward rotation & elevation
• Extension describes when the Humerus moves posteriorly and is paired with scapular downward rotation & depression

Movements of the Glenohumeral Joint - Horizontal Plane

• Horizontal Adduction means the Humerus moves toward and across the chest, paired with scapular protraction (abduction)
• Horizontal Abduction means the Humerus moves away from the chest, paired with scapular retraction (adduction)

Movements of the Glenohumeral Joint - Rotational Movements

• External Rotation describes when the Humerus rotates away from the midline, paired with scapular retraction
• Internal Rotation describes when the Humerus rotates toward the midline, paired with scapular protraction

Movements of the Glenohumeral Joint - Combined & Diagonal Movements

• Critical for throwing mechanics

• Diagonal abduction/adduction means a Combination of flexion, abduction, or extension, adduction

• A preferred approach is to break movements into cardinal planes instead of naming all combinations

• Circumduction is a combination of flexion, extension, abduction, adduction, & rotation

• The glenohumeral joint relies on ligaments, tendons, and scapular movement to maintain stability and prevent impingement while allowing a wide range of motion

Glenohumeral Adduction

• Glenohumeral Adduction is the Movement of the humerus toward the midline, typically from an abducted position. A pull-up can be an example
• Primary Muscles Involved for Adduction - Latissimus dorsi(major mover and aids in internal rotation and extension), Teres major (assists adduction, internal rotation, and extension), and the Lower pectoralis major (assists adduction, even when arm is not fully abducted)

Glenohumeral Extension

• Glenohumeral Extension is the Movement of the arm posteriorly in the sagittal plane
• Examples include a bent-over barbell row (shoulder extension with elbow flexion) or during paddling where the shoulder moves from a flexed to an extended position _ Primary Muscles Involved for Extension - Latissimus dorsi, Teres major , Lower pectoralis major (from a flexed position), and Triceps brachii (long head)

Glenohumeral Horizontal Abduction

• Glenohumeral Horizontal Abduction describes movement moving the arm backward in a horizontal plane, for example in a rear delt fly (posterior deltoid-driven movement) or tennis backhand (involves horizontal abduction, external rotation, and some flexion)
• Primary Muscles Involved - Posterior deltoid (main agonist), Infraspinatus (helps rotate and stabilize the humeral head), and Teres minor (works similarly to infraspinatus)

Glenohumeral External Rotation

• Glenohumeral External Rotation describes Rotating the humerus outward from the body, for example, a table tennis backhand stroke
• Primary muscles involved include the Infraspinatus (rotator cuff), Teres minor (rotator cuff), and the Posterior deltoid (minor role)

Glenohumeral Internal Rotation

• Glenohumeral Internal Rotation describes Rotating the humerus inward toward the body, for example during a Volleyball spike (starts in external rotation, then internally rotates to accelerate the arm) or a Baseball pitch (when moving from external to internal rotation for ball release)
• Primary muscles involved include the Latissimus dorsi, Teres major, Pectoralis major, and Subscapularis(rotator cuff, which is the primary internal rotator and located on the anterior scapula)

Rotator Cuff Muscles & Their Roles

• Infraspinatus is for External rotation, horizontal abduction, extension, and stabilization

• Teres minor is for External rotation, horizontal abduction, extension, and stabilization

• Subscapularis is for Internal rotation, adduction, extension, and stabilization

• Shoulder movements often involve coordinated elbow motion

• Many muscles contribute to multiple shoulder actions _ The rotator cuff muscles play a major role in stabilizing the humeral head

• Overhead athletes, like pitchers, often experience rotator cuff injuries due to repetitive stresses

Shoulder Girdle Muscles - Anterior Muscle: Pectoralis Minor

• Originates on the 3rd to 5th ribs (anterior surfaces)
• Insertion is on the Coracoid process of the scapula
• Actions are Abduction (transverse plane), Downward rotation (frontal plane), and Depression
• Innervation occurs via the Medial pectoral nerve (C8, T1)
• To Palpate go Deep under pectoralis major, inferior to the coracoid process

Shoulder Girdle Muscles - Posterior & Lateral Muscle: Serratus Anterior

• Originates on the Upper nine ribs (lateral chest)
• Insertion is on the Medial border of scapula (anterior aspect)
• Actions include Abduction (transverse plane), Upward rotation (frontal plane)
• Innervation occurs via the Long thoracic nerve (C5–C7)
• To Palpate find the Lateral chest below ribs 5–6; best felt with arm flexed at 90°

Shoulder Girdle Muscles - Posterior Muscles: Trapezius

• Upper Fibers Origin is at the Base of skull, occipital protuberance, posterior neck ligaments
• Upper Fibers Insertion is at the Lateral 3rd of clavicle (posterior aspect)
  • Upper Fiber actions include Elevation (frontal plane), Upward rotation (frontal plane), Extension of head (sagittal plane), and Rotation of head (transverse plane)
  • Innervation occurs via the Spinal accessory nerve (C3, C4)
• Upper Fibers may be Palpated between the Occipital bone & C6, lateral to acromion
• Middle Fibers Origin is at the Spinous process of C7-T3
• Middle Fibers Insertion is at the Medial border of acromion, superior scapular spine
  • Middle Fiber Actions include Elevation (frontal plane), Adduction (transverse plane), Upward rotation (frontal plane)
  • Middle Fibers can be Palpated from C7 to T3, laterally to acromion
• Lower Fibers Origin is at the Spinous process of T4-T12
• Lower Fibers Insertion is at the Triangular base of scapular spine
  • Lower Fiber Actions include Adduction (transverse plane), Depression (frontal plane), Upward rotation
  • Lower Fibers can be Palpated from T4-T12, medial to scapular spine

Shoulder Girdle Muscles - Posterior Muscles: Rhomboids (Major & Minor)

• Origin is at the Spinous processes of C7-T5
• Insertion is at the Medial border of scapula (below scapular spine)
  • Actions include Adduction (transverse plane), Downward rotation (frontal plane), and Elevation (frontal plane)
  • Innervation occurs via the Dorsal scapular nerve (C5)
  • May be Palpated deep to trapezius, best felt with hand behind back and lifted

Shoulder Girdle Muscles Leavtor Scapulae

• Origin is at the Transverse processes of C1-C4
• Insertion is at the Medial border of scapula (superior angle to scapular spine)
  • Primary Action is Elevation (frontal plane)
  • Innervation is via the Dorsal scapular nerve (C5), branches of C3-C4
  • Can be palpated deep to trapezius, best felt medial to superior scapular angle