Shoulder Complex Anatomy Quiz

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Questions and Answers

What is the primary function of the sternoclavicular joint?

Allows rotation of the scapula

Facilitates humeral flexion

Links the upper extremity to the trunk (correct)

Stabilizes the glenohumeral joint

Which ligament is the principal stabilizer of the sternoclavicular joint?

Anterior SC Ligament

Coracoclavicular Ligament

Costoclavicular Ligament (correct)

Interclavicular Ligament

What movement is defined as 'scaption'?

Elevation in the plane of the scapula (correct)

Internal rotation of the shoulder

Horizontal adduction of the arm

Protraction of the scapula

What is the angle of inclination of the humerus in relation to the humeral shaft?

135º Signup and view all the answers

Which joint is known to be most mobile in the body?

Glenohumeral Joint Signup and view all the answers

During upward rotation of the scapula, which two movements occur at the sternoclavicular and acromioclavicular joints?

Elevation at SC and upward rotation at AC Signup and view all the answers

Which ligament in the glenohumeral joint is the strongest supporting ligament?

Coracohumeral Ligament Signup and view all the answers

What does dynamic stability at the glenohumeral joint rely on?

Active muscle contraction Signup and view all the answers

Which joint movement occurs in the transverse plane at the acromioclavicular joint?

Internal/External Rotation Signup and view all the answers

What limits excessive anterior and posterior movement at the sternoclavicular joint?

Anterior & Posterior SC Ligaments Signup and view all the answers

What is the function of the glenoid labrum in the glenohumeral joint?

Deepen the glenoid fossa Signup and view all the answers

Which movement occurs at the glenohumeral joint when the humerus moves posteriorly?

External Rotation Signup and view all the answers

What is the role of the coracoacromial arch?

Protects against inferior migration of the humeral head Signup and view all the answers

How much humeral flexion typically occurs at the glenohumeral joint?

120º Signup and view all the answers

What is the primary action of the serratus anterior muscle?

Scapular abduction and upward rotation Signup and view all the answers

Which muscles work together in the downward rotation force couple?

Rhomboids and Pectoralis Minor Signup and view all the answers

What is the role of the upper trapezius during shoulder elevation?

Elevates and upwardly rotates the scapula Signup and view all the answers

How does the pectoralis minor affect scapular movement?

It anteriorly tilts and depresses the scapula Signup and view all the answers

Which muscles are involved in pure retraction of the scapula?

Middle Trapezius and Rhomboids Signup and view all the answers

What is the defining action of the deltoid muscle's anterior fibers?

Flexion and horizontal adduction of the humerus Signup and view all the answers

Which force couple is primarily responsible for the upward rotation of the scapula?

Upper Trapezius and Serratus Anterior Signup and view all the answers

What is a common underactive condition of the pectoralis minor?

Poor scapular stability during weight-bearing tasks Signup and view all the answers

What is the action of the subscapularis muscle?

Internal rotation of the humerus Signup and view all the answers

Which functional movements involve scapular upward rotation?

Pushing and throwing Signup and view all the answers

What is the primary mover in the elevation force couple?

Upper Trapezius Signup and view all the answers

Which muscle stabilizes the scapula to the thoracic cage?

Rhomboids Signup and view all the answers

What is the effect of tightness in the infraspinatus and teres minor?

Limited range of motion into internal rotation and horizontal adduction Signup and view all the answers

Study Notes

Shoulder Complex Overview

Comprises four joints: Sternoclavicular (SC), Acromioclavicular (AC), Glenohumeral (GH), and Scapulothoracic (ST).
Essential for linking upper extremity to the trunk and facilitating extensive arm mobility.
Provides stability necessary for fine and gross motor tasks at the elbow, wrist, and hand.

Scapula Anatomy and Positioning

Features three angles: inferior, superior, and lateral; three borders: medial, lateral, and superior.
Resting position aligns: superior angle with thoracic vertebra 2 (T2), spine of the scapula with T3, inferior angle with T7.
Slight upward rotation (5º-10º) in the frontal plane; anterior tilt of the scapula noted.

Plane of the Scapula

Positioned at a 30º to 45º angle to the frontal plane for stress reduction during daily activities.
Scapular motion in this plane is crucial for shoulder joint stability and function.

Humerus Alignment

Humerus has a 135º angle of inclination; retroversion (30º-45º) aligns it with the scapular plane.
These anatomical features enhance stability of the GH joint.

Clavicle Features

Curved S-shaped structure resting at a 20º angle posterior to the frontal plane and slightly elevated.

Sternoclavicular Joint (SC)

Only true articulation connecting upper extremity to axial skeleton, classified as a diarthrodial saddle joint.
Allows three degrees of freedom: elevation/depression, protraction/retraction, and posterior rotation.
Costoclavicular ligament primarily stabilizes SC joint, limiting motion except for depression.

Acromioclavicular Joint (AC)

Plane synovial joint offering three degrees of freedom, important for maintaining scapuloclavicular relationships.
Key ligaments for stability include the coracoclavicular ligament and superior/inferior AC ligaments.

Scapulothoracic Joint (ST)

Functions as a joint without traditional anatomical structure, pivotal for scapular motion during arm activity.
Movement correlates to scapular elevation/depression, protraction/retraction, and upward/downward rotation.

Glenohumeral Joint (GH)

Most mobile joint in the body, functioning as a diarthrodial ball-and-socket joint with a large humeral head and smaller glenoid fossa.
Only 25%-33% of the humeral head articulates with the glenoid, maximizing mobility but sacrificing stability.

GH Joint Stability

Glenoid labrum deepens the fossa, increasing stability and reducing humeral head translation.
Capsuloligamentous complex allows high mobility while stabilizing the joint through ligaments like the coracohumeral and glenohumeral ligaments.

Movement Mechanics of the GH Joint

Offers three degrees of freedom: flexion/extension, abduction/adduction, and internal/external rotation.
Critical to maintain arthrokinematic principles during movements to prevent impingement and optimize function.

Scapulohumeral Rhythm

Coordinated movements across all four shoulder joints enhance overall shoulder complex functionality.
Follows a 2:1 ratio of GH movement to ST upward rotation for optimum motion and stability.

Muscle Function in Shoulder Dynamics

Axioscapular muscles (trapezius, serratus anterior, levator scapula, rhomboids, pectoralis minor) play essential roles in stabilizing the scapula and supporting shoulder movements.
Trapezius functions include elevation and upward rotation, while serratus anterior aids in scapular abduction and stabilization on the thoracic cage.

Clinical Notes

Underactive or overactive muscular dynamics can lead to dysfunction, such as scapular winging or elevated shoulder posture.
Rehabilitation and strengthening exercises should emphasize maintaining proper movement mechanics and muscle balance.### Shoulder Complex Overview
True weakness can result from other joint limitations, such as glenohumeral (GH) internal rotation range of motion (ROM) affecting scapular positioning.
Tightness may lead to protracted scapulae, impacting functional movements like pushing, throwing, and reaching.

Upward Rotation Force Couple

Involves synergistic action of trapezius and serratus anterior for scapular upward rotation.
Trapezius acts in three segments:
- Upper: Elevates distal clavicle and acromion.
- Middle: Adducts scapula.
- Lower: Depresses medial spine of scapula.
Serratus anterior elevates and abducts the scapula.

Axioscapular Muscles

Levator Scapula

Function: Elevates and downwardly rotates scapula; facilitates lateral neck flexion and cervical spine extension.
Innervation: Dorsal Scapular Nerve.
Overactive in downwardly rotated and elevated scapula scenarios.

Rhomboids

Function: Scapular adduction (retraction) and stabilization.
Innervation: Dorsal Scapular Nerve.
Overactive when scapula is adducted and downwardly rotated; underactive when shoulders are rounded.

Pectoralis Minor

Actions: Anterior tilt, depression, and downward rotation of scapula.
Innervation: Medial and Lateral Pectoral Nerves.
Overactivity can risk impingement through increased internal rotation of the scapula during movement.

Elevation and Retraction Force Couples

Elevation: Involves upper trapezius and levator scapula working together.
Retraction: Middle trapezius, lower trapezius, and rhomboids coordinate to achieve pure retraction motion.

Axiohumeral Muscles

Major muscles: Latissimus Dorsi and Pectoralis Major, responsible for gross motor movements of the GH joint.

Latissimus Dorsi

Actions: Extension, adduction, and internal rotation of humerus; aids in climbing.
Innervation: Thoracodorsal Nerve.
Overactivity can limit shoulder flexion and external rotation.

Pectoralis Major

Actions: Flexion, adduction, internal rotation, and horizontal adduction of humerus.
Innervation: Medial and Lateral Pectoral Nerves.
Dysfunction leads to reduced strength in various motions.

Shoulder Girdle Movements

Depression: Involves lower trapezius, pec minor, and latissimus dorsi.
Protraction: Engages serratus anterior and pectoralis major.

Scapulohumeral Muscles

Function: Provide motion and dynamic stabilization to GC joint. Key muscles include deltoid, supraspinatus, infraspinatus, teres minor, subscapularis, teres major, and coracobrachialis.

Deltoid

Actions: Abduction, flexion, horizontal adduction, and internal rotation.
Innervation: Axillary Nerve.
Dysfunction results in compensatory movements or limited ROM.

Supraspinatus

Key for initiating abduction in the scapular plane; also stabilizes GH joint.
Innervation: Suprascapular Nerve.

Infraspinatus and Teres Minor

Work synergistically for external rotation and horizontal abduction of the humerus.

Subscapularis

Primary mover for internal rotation of humerus; stabilizes GH joint.
Innervation: Upper and Lower Subscapular Nerves.

Rotator Cuff Functions

Critical for humeral head stability during arm movements, counteracting superior translations resulting from deltoid action.

Dynamic Stability and Kinematics

Each muscle contributes specific actions, with synergistic efforts stabilizing the humerus and maintaining shoulder integrity.

Functional Motion Dynamics

Internal Rotation: Primarily driven by subscapularis and assisted by latissimus dorsi and pectoralis major.
External Rotation: Infraspinatus, teres minor, and posterior deltoid are the main movers.

Relationship of Shoulder to Spine

Coordination between shoulder girdle and spine is essential for optimal movement; poor posture in one often affects the other.

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Description

Test your knowledge on the anatomy and function of the shoulder complex. This quiz covers the four main joints: the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic joints. Understand their roles in providing mobility and stability to the upper extremity.