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Questions and Answers
Which muscle is primarily responsible for the internal rotation of the humerus?
Which muscle is primarily responsible for the internal rotation of the humerus?
What movement does the serratus anterior muscle facilitate?
What movement does the serratus anterior muscle facilitate?
Which joint is comprised of the glenoid cavity of the scapula and the head of the humerus?
Which joint is comprised of the glenoid cavity of the scapula and the head of the humerus?
Which function is NOT associated with the shoulder girdle?
Which function is NOT associated with the shoulder girdle?
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The trapezius muscle's upper fibers are involved in which action?
The trapezius muscle's upper fibers are involved in which action?
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What type of movements does the deltoid muscle primarily facilitate?
What type of movements does the deltoid muscle primarily facilitate?
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Which action is performed by the rhomboids?
Which action is performed by the rhomboids?
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Which muscle acts to stabilize the sternoclavicular joint?
Which muscle acts to stabilize the sternoclavicular joint?
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What is the maximum degree of flexion possible at the Glenohumeral Joint?
What is the maximum degree of flexion possible at the Glenohumeral Joint?
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Which ligaments are part of the capsuloligamentous complex of the Glenohumeral Joint?
Which ligaments are part of the capsuloligamentous complex of the Glenohumeral Joint?
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What mechanism is NOT considered a dynamic stabilization mechanism of the Glenohumeral Joint?
What mechanism is NOT considered a dynamic stabilization mechanism of the Glenohumeral Joint?
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Which of the following motions is limited to 70 degrees of rotation at the Glenohumeral Joint?
Which of the following motions is limited to 70 degrees of rotation at the Glenohumeral Joint?
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What is the main structural cause of primary impingement in the shoulder?
What is the main structural cause of primary impingement in the shoulder?
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In the context of the Glenohumeral Joint, how does the concave/convex rule apply?
In the context of the Glenohumeral Joint, how does the concave/convex rule apply?
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Which muscle is primarily involved in dynamic stabilization of the Glenohumeral Joint?
Which muscle is primarily involved in dynamic stabilization of the Glenohumeral Joint?
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What does secondary impingement typically result from?
What does secondary impingement typically result from?
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What is the primary function of the teres major muscle?
What is the primary function of the teres major muscle?
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Which muscles are primarily responsible for the upward rotation of the scapula?
Which muscles are primarily responsible for the upward rotation of the scapula?
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What action does the triceps brachii primarily perform at the shoulder joint?
What action does the triceps brachii primarily perform at the shoulder joint?
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What role do the conoid and trapezoid ligaments play in shoulder stabilization?
What role do the conoid and trapezoid ligaments play in shoulder stabilization?
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During arm abduction, which joint movements facilitate this action?
During arm abduction, which joint movements facilitate this action?
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Which muscles are considered the primary abductors of the arm?
Which muscles are considered the primary abductors of the arm?
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What describes the scapulothoracic articulation?
What describes the scapulothoracic articulation?
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What is the maximum axial rotation allowed at the sternoclavicular joint?
What is the maximum axial rotation allowed at the sternoclavicular joint?
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Study Notes
Shoulder: Clinical Anatomy & Biomechanics
- The shoulder complex consists of the glenohumeral, acromioclavicular, sternoclavicular joints, and the scapulothoracic articulation and subacromial space.
Shoulder Complex
- Glenohumeral Joint: The primary articulation connecting the humerus and the scapula.
- Acromioclavicular Joint: Connects the acromion process of the scapula and the clavicle.
- Sternoclavicular Joint: Connects the sternum and the clavicle.
- Scapulothoracic Articulation: The area where the scapula moves against the chest wall, although not a true joint, it allows for scapular movement.
- Subacromial Space: The area between the acromion, the humeral head and tendons, plays a major role in shoulder movement/function.
Anatomical Orientation of the Shoulder Complex
- The scapular plane is oriented at a 35-degree angle from the sagittal plane.
- The humerus has a 30-degree retroversion.
- The clavicle sits at a 20-degree angle with the scapula.
Stability Functions of Shoulder Girdle
- Provides a stable base for shoulder muscles to generate force.
- Shoulder girdle muscles act as stabilizers.
- Correct force-length relationships are maintained.
- Shoulder joint congruence is maximized.
Mobility Functions of the Shoulder Girdle
- Permits the largest range of motion (ROM) of any complex in the body.
- The scapulohumeral rhythm allows for increased ROM with less compromise of stability (4 joints vs 1 joint).
- Facilitates movements of the upper extremity by positioning the glenohumeral joint favorably.
Shoulder Girdle Motion
- Elevation/Depression: Upward/Downward movement
- Protraction/Retraction (Abduction/Adduction): Forward/Backward movement
- Upward/Downward rotation: Rotation of the scapula
Shoulder Joint Movements
- Flexion/Extension: Bending and straightening the arm
- Abduction/Adduction: Moving the arm away from and towards the body
- Horizontal Abduction/Adduction: Moving the arm horizontally away from and towards the body
- Diagonal Abduction/Adduction: Moving the arm diagonally away from and towards the body
- Outward/Inward Rotation: Rotating the arm externally and internally
Muscular Considerations
- The muscles of the scapula and humerus are critical for the range of motion (ROM) of the shoulder.
Shoulder Girdle Muscles
- Pectoralis Minor: Downward rotation, depression, and protraction of the scapula.
- Serratus Anterior: Protraction and upward rotation of the scapula.
- Subclavius: Stabilizes the sternoclavicular joint.
- Levator Scapulae: Elevation and downward rotation of the scapula.
- Rhomboids: Downward rotation, retraction, and elevation of the scapula.
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Trapezius (Upper, Middle, Lower):
- Upper: Elevation, upward rotation of scapula.
- Middle: Retraction of scapula.
- Lower: Depression, retraction of scapula
Shoulder Joint Muscles
- Pectoralis Major: Flexion, horizontal adduction, and internal rotation of the humerus.
- Deltoid: Nearly all arm movements from the shoulder joint (internal rotation, abduction, hyperextension, flexion, horizontal adduction).
- Coracobrachialis: Forward movements of the humerus.
- Subscapularis: Internal rotation of the humerus, stabilizing the glenohumeral joint.
- Biceps Brachii: Flexion and adduction, and horizontal adduction.
- Supraspinatus: Abduction of the humerus.
- Infraspinatus: External rotation, horizontal abduction, and stabilizes the humerus during flexion.
- Teres Minor: External rotation, horizontal abduction, and stabilizes the humerus during flexion.
- Latissimus Dorsi: Extension and adduction of the arm.
- Teres Major: Shoulder extension, adduction, and medial rotation.
- Triceps Brachii: Adduction, extension, and hyperextension of the humerus.
Scapulothoracic Muscles
- Elevators (Upper): Trapezius, Levator scapulae, Rhomboids
- Depressors (Lower): Trapezius, Pectoralis minor
- Protractors: Serratus anterior, Pectoralis minor
- Retractors: Mid and Lower Trapezius, Rhomboids, Levator scapulae
- Upward Rotators: Serratus anterior, Upper Trapezius
- Downward Rotators: Rhomboids, Pectoralis minor, Levator scapulae
Glenohumeral Joint Muscles
- Abductors: Deltoid, Supraspinatus
- Adductors: Pectoralis major, Latissimus dorsi, Teres major
- Internal Rotators: Pectoralis major, Subscapularis, Anterior deltoid, Latissimus dorsi, Teres major
- External Rotators: Infraspinatus, Teres minor, Posterior deltoid
- Flexors: Biceps brachii, Coracobrachialis, Anterior deltoid
- Extensors: Triceps brachii, Posterior deltoid, Latissimus dorsi, Teres major
Specific Joints Structure and Function
- Sternoclavicular Joint: Clavicle, Sternum, 1st Rib, Sternoclavicular ligaments, Costoclavicular ligament, Articular disc. Muscular attachments.
- Sternoclavicular Joint Motions: Elevation/Depression, Protraction/Retraction, Axial Rotation.
Acromioclavicular Joint
- Gliding/Planar Joint: Articulating surfaces glide over one another, rather than hinge-like or ball-and-socket joint.
- Acromioclavicular Ligament: Connects the acromion and clavicle
- Coracoclavicular Ligament (Conoid/Trapezoid): Connects the coracoid process and clavicle:
- Articular Disc: Provides cushion between bones.
- Acromioclavicular Joint Motions: Upward/Downward rotation and Horizontal & sagittal plane adjustments.
Coracoclavicular Ligaments
- Conoid Ligament (medial): Connects acromion to the clavicle,
- Trapezoid Ligament (lateral): Connects acromion to the clavicle,
- Maintains the acromioclavicular joint, supports the scapula.
Scapulothoracic Articulation
- Not a true synovial joint
- Provides movement base for the humerus
- AC joint + SC joint motion = ST joint motion
Primary Movements of Scapulothoracic Articulation
- Elevation and Depression
- Retraction and Protraction
- Downward and Upward rotation
Scapulothoracic Elevation
- SC joint elevation + AC joint downward rotation = ST Elevation
Scapulothoracic Upward Rotation
- SC joint elevation + AC joint upward rotation = ST Upward rotation
Scapular Rotation
- Enhances glenohumeral stability
- Elevates the acromion to avoid impingement
- Maintains effective length tension relationship for scapulohumeral muscles
Glenohumeral Joint
- Humeral Head: Ball-shaped end of the humerus
- Glenoid Fossa: Socket of the scapula
- Glenoid Labrum: Ring of cartilage that deepens the glenoid fossa
- Rotator Cuff Muscles (SITS): Supraspinatus, Infraspinatus, Teres Minor, Subscapularis
- Capsuloligamentous Complex: Capsules and ligaments surrounding the joint
- Coracohumeral Ligament: Reinforces joint capsule
- Long Head of Biceps: Connects to joint
- Subacromial Space: Space between acromion, humeral head and rotator cuff tendons.
Glenohumeral Ligaments
- SGHL: Superior glenohumeral ligament
- MGHL: Middle glenohumeral ligament
- IGHL: Inferior glenohumeral ligament (complex of anterior and posterior bands, and axillary pouch).
Coracohumeral Ligament
- Anterior and Posterior bands
Glenohumeral Joint Motions
- Flexion/Extension, Abduction/Adduction, Internal/External Rotations
- Cannot be isolated from other shoulder girdle elements
Glenohumeral Joint Stability
- Static restraints (Bony structures, Labrum, Capsuloligamentous structure, Negative joint pressure)
- Dynamic restraints (Rotator Cuff, Biceps, Proprioceptive receptors, Neuromotor coordination)
Kinematics and Biomechanics
- Convex Concave Rules: Describes rolling and gliding motions between joint surfaces.
- Normal Arthrokinematics: How the surfaces of a joint move in relation to one another (glenohumeral joint). Rotation and translation are combined, with joint surfaces trying to maintain humeral head center within the glenoid.
Glenohumeral Roll/Glide
- Describe glenohumeral joint surface movement during shoulder actions.
Glenohumeral Joint Motions: Abnormal Arthrokinematics
- Capsular tightness
- Rotator cuff tears
Clinical Implication
- Clinical Relevance to Subacromial Space: Avoid impingement by appropriately rotating the humerus and upward rotation of scapula to elevate the lateral end of the acromion.
- Primary impingement: Structural stenosis of subacromial space.
- Secondary impingement: Functional stenosis of subacromial space due to abnormal arthrokinematics.
Dynamic Stabilization Mechanisms
- Passive muscle tension
- Compressive muscles from muscle contraction
- Joint motion that results in passive structure tightening.
- Redirection of joint force toward the center of the glenohumeral joint.
Dynamic Stabilization Mechanisms
- Force-length relationships vary due to multiple joints.
- Tension development in agonist and antagonist muscles is important for preventing humeral head dislocation.
- Force couples—two or more forces acting on an object where the forces are equal and opposite.
Force Couples Acting on Glenohumeral Joint
- Anterior/Posterior rotator cuff muscles (transverse plane).
- Deltoid versus inferior rotator cuff muscles (coronal plane)
Force Couples Disruption
Rotator Cuff Muscles
- Supraspinatus
- Infraspinatus
- Teres Minor
- Subscapularis
Rotator Cuff – Dynamic GH Stabilizer
Rotator Cuff Function
- Approximates the humerus to function
- Supraspinatus assists the deltoid in abduction
- Subscapularis, Infraspinatus & Teres minor depress the humeral head
Scapulo humeral rhythm
- Movement relationship between humerus and scapula during arm raising motions.
- 2:1 ratio: for every 3 degrees of shoulder abduction, 2 degrees occur at the GH joint and 1 degree occurs at the SC joint.
Scapulo humeral rhythm Clinical Implications
- Rotator cuff pain in early phase of active abduction
- Impingement pain in mid phase of active abduction
- AC pain in later phase of active abduction
Effects of Poor Scapular Stabilization
- Poor resting posture of the scapula
- Loss of upward or optimal tilt of scapula
- Loss of static stability of the glenohumeral joint
- Inferior translation and internal rotation of humeral head
- Traction ischemia in rotator cuff (especially supraspinatus) muscles
- Capsular laxity
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Description
Explore the intricate anatomy and biomechanics of the shoulder complex, including the glenohumeral, acromioclavicular, and sternoclavicular joints. This quiz examines the functional roles of various components and their anatomical orientations. Test your knowledge on how these structures work together for optimal shoulder movement.
