Chapter 5: Shoulder Joint Anatomy & Movement

Chapter 5 **Overview** - The shoulder joint is highly mobile, allowing movement in all planes. - Works in conjunction with the **shoulder girdle** (scapula + clavicle). - **Trade-off:** More mobility = Less stability → Higher risk of injury. **Structure & Stability** - The...

Chapter 5 **Overview** - The shoulder joint is highly mobile, allowing movement in all planes. - Works in conjunction with the **shoulder girdle** (scapula + clavicle). - **Trade-off:** More mobility = Less stability → Higher risk of injury. **Structure & Stability** - The **glenoid fossa** is **shallow**, allowing wide **range of motion (ROM)**. - The **humeral head** fits loosely, increasing motion but reducing stability. - **Laxity:** Loose connective tissue allows extreme mobility but increases risk of **dislocations, subluxations, and rotator cuff impingements**. **Shoulder Joint Movements & Pairings** - Shoulder movements are paired with **scapular (shoulder girdle) movements**. - Example: **Abduction of the shoulder** → **Upward rotation of the scapula**. - Internal/External rotation involves **abduction/adduction of the scapula**. **Planes of Motion** - **Sagittal Plane:** Flexion/Extension. - **Frontal Plane:** Abduction/Adduction. - **Horizontal Plane:** Horizontal abduction/adduction. - **Transverse Plane:** Internal/External rotation. **Key Bony Landmarks** **Scapula** - **Glenoid fossa** -- Shallow socket for humeral head. - **Acromion process** -- Connects to clavicle (AC joint). - **Coracoid process** -- Anterior projection (Pec minor attachment). - **Scapular spine** -- Posterior ridge separating supraspinous/infraspinous fossae. - **Supraspinous fossa** -- Above the spine (Supraspinatus origin). - **Infraspinous fossa** -- Below the spine (Infraspinatus origin). - **Subscapular fossa** -- Anterior depression (Subscapularis origin). - **Inferior angle** -- Key landmark for scapular movement. - **Lateral/Medial borders** -- Muscle attachment sites. **Humerus** - **Humeral head** -- Articulates with glenoid fossa. - **Greater/Lesser tubercles** -- Muscle attachment sites. - **Intertubercular (Bicipital) groove** -- Pathway for biceps tendon. - **Deltoid tuberosity** -- Deltoid muscle insertion. **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 (dislocations, impingements).** **Glenohumeral Joint & Movements - Summary Notes** **Joint Structure & Stability** - **Glenohumeral joint**: Humeral head meets glenoid fossa. - **Ligaments**: Provide primary stability (anterior & inferior) while allowing flexibility. - **Superior glenohumeral ligament** - **Inferior glenohumeral ligament** - **Coracohumeral ligament** - **Glenoid labrum**: Cartilage ring enhancing stability. - **Tendons**: Surround ligaments, key for movement (e.g., supraspinatus, infraspinatus, teres minor). - **Scapular tracking**: Necessary to prevent impingement of tendons under the acromion. **Movements of the Glenohumeral Joint** 1. **Frontal Plane** - **Abduction**: Lateral upward movement of the humerus. - Requires **scapular upward rotation & elevation** to avoid impingement. - **Adduction**: Medial downward movement. - Paired with **scapular downward rotation**. - Can occur without crossing the midline. 2. **Sagittal Plane** - **Flexion**: Humerus moves anteriorly. - Paired with **scapular upward rotation & elevation**. - **Extension**: Humerus moves posteriorly. - Paired with **scapular downward rotation & depression**. 3. **Horizontal Plane** - **Horizontal Adduction**: Humerus moves toward and across the chest. - Paired with **scapular protraction (abduction)**. - **Horizontal Abduction**: Humerus moves away from the chest. - Paired with **scapular retraction (adduction)**. 4. **Rotational Movements** - **External Rotation**: Humerus rotates away from midline. - Paired with **scapular retraction**. - **Internal Rotation**: Humerus rotates toward midline. - Paired with **scapular protraction**. - Critical for **throwing mechanics**. **Combined & Diagonal Movements** - **Diagonal abduction/adduction**: Combinations of flexion, abduction, or extension, adduction. - **Preferred approach**: Break movements into **cardinal planes** instead of naming all combinations. - **Circumduction**: A combination of flexion, extension, abduction, adduction, & rotation. **Key takeaway**: 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** - **Definition**: Movement of the humerus toward the midline, typically from an abducted position. - **Example**: Pull-up -- humerus moves from an abducted to an adducted position. - **Primary Muscles Involved**: - **Latissimus dorsi** -- Major mover; also aids in internal rotation and extension. - **Teres major** -- Assists adduction, internal rotation, and extension. - **Lower pectoralis major** -- Assists adduction, even when arm is not fully abducted. **Glenohumeral Extension** - **Definition**: Moving the arm posteriorly in the sagittal plane. - **Examples**: - **Bent-over barbell row** -- Shoulder extension with elbow flexion. - **Paddling motion** -- Shoulder moves from a flexed to an extended position. - **Primary Muscles Involved**: - **Latissimus dorsi** - **Teres major** - **Lower pectoralis major** (from a flexed position) - **Triceps brachii (long head)** -- Assists in shoulder extension. **Glenohumeral Horizontal Abduction** - **Definition**: Moving the arm backward in a horizontal plane. - **Examples**: - **Rear delt fly** -- Posterior deltoid-driven movement. - **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. - **Teres minor** -- Works similarly to infraspinatus. **Glenohumeral External Rotation** - **Definition**: Rotating the humerus outward from the body. - **Example**: Table tennis backhand stroke. - **Primary Muscles Involved**: - **Infraspinatus** (rotator cuff) - **Teres minor** (rotator cuff) - **Posterior deltoid** (minor role) **Glenohumeral Internal Rotation** - **Definition**: Rotating the humerus inward toward the body. - **Examples**: - **Volleyball spike** -- Starts in external rotation, then internally rotates to accelerate the arm. - **Baseball pitch** -- Moves from external to internal rotation for ball release. - **Primary Muscles Involved**: - **Latissimus dorsi** - **Teres major** - **Pectoralis major** - **Subscapularis** (rotator cuff) -- Primary internal rotator, located on the anterior scapula. **Rotator Cuff Muscles & Their Roles** - **Infraspinatus** -- External rotation, horizontal abduction, extension, and stabilization. - **Teres minor** -- External rotation, horizontal abduction, extension, and stabilization. - **Subscapularis** -- Internal rotation, adduction, extension, and stabilization. **Key Takeaways** - 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 (e.g., pitchers) often experience **rotator cuff injuries** due to repetitive stresses. **Shoulder Girdle Muscles: Origins, Insertions, Actions, and Innervation** **Anterior Muscle** - **Pectoralis Minor** - **Origin:** 3rd to 5th ribs (anterior surfaces) - **Insertion:** Coracoid process of scapula - **Actions:** - Abduction (transverse plane) - Downward rotation (frontal plane) - Depression - **Innervation:** Medial pectoral nerve (C8, T1) - **Palpation:** Deep under pectoralis major, inferior to coracoid process **Posterior & Lateral Muscle** - **Serratus Anterior** - **Origin:** Upper 9 ribs (lateral chest) - **Insertion:** Medial border of scapula (anterior aspect) - **Actions:** - Abduction (transverse plane) - Upward rotation (frontal plane) - **Innervation:** Long thoracic nerve (C5--C7) - **Palpation:** Lateral chest below ribs 5--6; best felt with arm flexed at 90° **Posterior Muscles** - **Trapezius** - **Upper Fibers** - **Origin:** Base of skull, occipital protuberance, posterior neck ligaments - **Insertion:** Lateral 3rd of clavicle (posterior aspect) - **Actions:** - Elevation (frontal plane) - Upward rotation (frontal plane) - Extension of head (sagittal plane) - Rotation of head (transverse plane) - **Innervation:** Spinal accessory nerve (C3, C4) - **Palpation:** Between occipital bone & C6, lateral to acromion - **Middle Fibers** - **Origin:** Spinous process of C7-T3 - **Insertion:** Medial border of acromion, superior scapular spine - **Actions:** - Elevation (frontal plane) - Adduction (transverse plane) - Upward rotation (frontal plane) - **Palpation:** C7 to T3, laterally to acromion - **Lower Fibers** - **Origin:** Spinous process of T4-T12 - **Insertion:** Triangular base of scapular spine - **Actions:** - Adduction (transverse plane) - Depression (frontal plane) - Upward rotation - **Palpation:** T4-T12, medial to scapular spine - **Rhomboids (Major & Minor)** - **Origin:** Spinous processes of C7-T5 - **Insertion:** Medial border of scapula (below scapular spine) - **Actions:** - Adduction (transverse plane) - Downward rotation (frontal plane) - Elevation (frontal plane) - **Innervation:** Dorsal scapular nerve (C5) - **Palpation:** Deep to trapezius, best felt with hand behind back and lifted - **Levator Scapulae** - **Origin:** Transverse processes of C1-C4 - **Insertion:** Medial border of scapula (superior angle to scapular spine) - **Action:** Elevation (frontal plane) - **Innervation:** Dorsal scapular nerve (C5), branches of C3-C4 - **Palpation:** Deep to trapezius, best felt medial to superior scapular angle