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Questions and Answers
The angle of inclination of the humeral shaft is 135°.
The angle of inclination of the humeral shaft is 135°.
True
The glenoid cavity is smaller than the humeral head.
The glenoid cavity is smaller than the humeral head.
True
The longitudinal diameter of the humeral head is 2.3 times larger than that of the glenoid fossa.
The longitudinal diameter of the humeral head is 2.3 times larger than that of the glenoid fossa.
False
The glenoid labrum is a ring of muscle attached to the margin of the glenoid cavity.
The glenoid labrum is a ring of muscle attached to the margin of the glenoid cavity.
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The angle of retroversion with the coronal plane is 45°.
The angle of retroversion with the coronal plane is 45°.
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The greater tuberosity of the humerus points anteriodly.
The greater tuberosity of the humerus points anteriodly.
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The glenoid labrum deepens the articular groove by up to 50%.
The glenoid labrum deepens the articular groove by up to 50%.
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Removal of the glenoid labrum decreases the chance of instability.
Removal of the glenoid labrum decreases the chance of instability.
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The inferior portion of the glenoid labrum is loosely attached and highly mobile.
The inferior portion of the glenoid labrum is loosely attached and highly mobile.
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The anatomical neck of the humerus makes an angle of 45° with the horizontal plane.
The anatomical neck of the humerus makes an angle of 45° with the horizontal plane.
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The coracoclavicular ligament consists of two parts: the conoid and the trapezoid.
The coracoclavicular ligament consists of two parts: the conoid and the trapezoid.
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The acromioclavicular joint is primarily stabilized by the scapulohumeral ligament.
The acromioclavicular joint is primarily stabilized by the scapulohumeral ligament.
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The conoid ligament primarily provides resistance in the lateral direction.
The conoid ligament primarily provides resistance in the lateral direction.
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The coracoclavicular ligament absorbs more energy than most other ligaments of the shoulder.
The coracoclavicular ligament absorbs more energy than most other ligaments of the shoulder.
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The acromioclavicular joint allows for extensive motion of the clavicle.
The acromioclavicular joint allows for extensive motion of the clavicle.
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Tension in the trapezoid portion of the coracoclavicular ligament prevents medial displacement of the scapula’s acromion.
Tension in the trapezoid portion of the coracoclavicular ligament prevents medial displacement of the scapula’s acromion.
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The SC joint and AC joint serve the same primary function.
The SC joint and AC joint serve the same primary function.
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The coracoclavicular ligament plays a critical role in coupling the rotation of the clavicle to the scapula.
The coracoclavicular ligament plays a critical role in coupling the rotation of the clavicle to the scapula.
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The superior capsular ligament is reinforced by attachments from the pectoralis and latissimus dorsi muscles.
The superior capsular ligament is reinforced by attachments from the pectoralis and latissimus dorsi muscles.
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The broad ligament provides posterior restraint to the GH joint.
The broad ligament provides posterior restraint to the GH joint.
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The inferior glenohumeral ligament is attached along the posterior-inferior rim of the glenoid fossa.
The inferior glenohumeral ligament is attached along the posterior-inferior rim of the glenoid fossa.
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The anterior band of the inferior GH ligament provides primary restraint to anterior translation of the humeral head.
The anterior band of the inferior GH ligament provides primary restraint to anterior translation of the humeral head.
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The coracoacromial arch is composed of the coracoid process, the acromion, and the coracoacromial ligament.
The coracoacromial arch is composed of the coracoid process, the acromion, and the coracoacromial ligament.
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The subacromial space houses the supraspinatus muscle and tendon.
The subacromial space houses the supraspinatus muscle and tendon.
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The inferior GH ligament becomes most taut in about 30 degrees of GH joint abduction.
The inferior GH ligament becomes most taut in about 30 degrees of GH joint abduction.
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The long head of the biceps is located in the subacromial space.
The long head of the biceps is located in the subacromial space.
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The middle GH ligament is effective at limiting internal rotation.
The middle GH ligament is effective at limiting internal rotation.
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Multiple separate bursae exist around the shoulder.
Multiple separate bursae exist around the shoulder.
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The axillary pouch helps in cradling the suspended humeral head during joint movement.
The axillary pouch helps in cradling the suspended humeral head during joint movement.
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The line of gravity creates an upward force on the humerus.
The line of gravity creates an upward force on the humerus.
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In a healthy GH joint, there is a positive intra-articular pressure.
In a healthy GH joint, there is a positive intra-articular pressure.
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The deltoid muscle helps stabilize the arm when there is an extreme vertical load pulling it down.
The deltoid muscle helps stabilize the arm when there is an extreme vertical load pulling it down.
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Static stabilization is solely dependent on passive forces in the GH joint.
Static stabilization is solely dependent on passive forces in the GH joint.
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The primary rotational movements at the GH joint include flexion, extension, internal rotation, and external rotation.
The primary rotational movements at the GH joint include flexion, extension, internal rotation, and external rotation.
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The deltoid muscle is the only prime mover for GH abduction and flexion.
The deltoid muscle is the only prime mover for GH abduction and flexion.
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The degree of glenoid inclination plays no role in the stability of the GH joint.
The degree of glenoid inclination plays no role in the stability of the GH joint.
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The rotator cuff muscles enhance the stability of the humeral head in the glenoid cavity.
The rotator cuff muscles enhance the stability of the humeral head in the glenoid cavity.
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The GH joint has two degrees of freedom.
The GH joint has two degrees of freedom.
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During adduction, both bands involved become slack.
During adduction, both bands involved become slack.
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The supraspinatus muscle is recruited to assist with static stabilization under heavy loading conditions.
The supraspinatus muscle is recruited to assist with static stabilization under heavy loading conditions.
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The inferior translatory force of the rotator cuff muscles compensates for the superior force of the deltoid muscle.
The inferior translatory force of the rotator cuff muscles compensates for the superior force of the deltoid muscle.
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Horizontal adduction and abduction are classified as the primary rotational motions at the GH joint.
Horizontal adduction and abduction are classified as the primary rotational motions at the GH joint.
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The anterior deltoid is not significantly involved in GH flexion.
The anterior deltoid is not significantly involved in GH flexion.
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The rotator interval capsule includes the superior GH ligament.
The rotator interval capsule includes the superior GH ligament.
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The force component that contributes to the rotation of the humerus during abduction is larger than the force directed superiorly.
The force component that contributes to the rotation of the humerus during abduction is larger than the force directed superiorly.
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Study Notes
Acromioclavicular Joint
- Surrounded by a capsule reinforced by superior and inferior ligaments
- Superior capsular ligament is reinforced by the deltoid and trapezius muscles
- Coracoclavicular ligament (CCL) provides stability and consists of two parts:
- Trapezoid ligament (lateral): resists posterior translation forces
- Conoid ligament (medial): restrains movement in superior and inferior directions
Acromioclavicular Joint - Stability
- The CCL is strong and absorbs more energy than other shoulder ligaments
- Provides horizontal and superior stability, preventing superior clavicle dislocation
- Limits upward rotation of the scapula at the AC joint
- Prevents medial displacement of the scapula's acromion by transferring force to the clavicle and SC joint
Acromioclavicular Joint - Mobility
- Permits subtle movements between the scapula and lateral end of the clavicle
- Forms an angle of 135° (angle of inclination) with the humeral shaft
- Forms an angle of 30° (retroversion angle) with the coronal plane
The Glenohumeral (Shoulder) Joint
- Glenoid cavity of the scapula is located at the superolateral angle and points laterally, anteriorly, and slightly superiorly
- Glenoid cavity is biconcave vertically and transversely, but less concave than the humeral head
- Smaller than the humeral head
- Longitudinal diameter of the humeral head is 1.9 times larger than the glenoid fossa's longitudinal diameter
- Transverse diameter of the humeral head is 2.3 times larger than the glenoid fossa's transverse diameter
- Glenoid labrum is a ring of fibrocartilage that deepens the glenoid cavity to increase congruence
The Glenoid Labrum (Right Shoulder)
- 12 hours: origin of the long head of the biceps
- 3 hours: anterior part
- 9-3 hours: loosely attached
- 2-3 hours (superiorly): may not be fixed
- Inferior portion is firmly attached and immobile
- Serves as the attachment site for the glenohumeral ligaments
- Removal increases the chance of instability
- Deepens the articular groove by up to 50%
Glenohumeral Ligaments
- The middle glenohumeral ligament limits external rotation
- Slackens upon internal rotation
The Inferior Glenohumeral Ligament
- Attaches proximally to the anterior-inferior glenoid fossa and labrum (4-8 o'clock)
- Distally attaches to the anterior-inferior and posterior-inferior margins of the anatomical neck, forming a "hammock"
- The axillary pouch is most taut at 90 degrees of GH joint abduction
- Acts as a sling, resisting inferior, anterior, and posterior translations
The Coracoacromial Arch
- Formed by the coracoid process, acromion, and coracoacromial ligament
- Serves as the functional "roof" of the GH joint
- Contains:
- Supraspinatus muscle and tendon
- Subacromial bursa
- Long head of the biceps
- Part of the superior capsule
- Prevents superior dislocation of the humeral head
The Bursae
- Multiple bursae exist around the shoulder
- Line of gravity creates a downward force on the humerus
- Tension in the rotator interval capsule creates a line of force that compresses the humeral head into the lower portion of the glenoid fossa
- Negative intra-articular pressure provides static stability
- Glenoid inclination provides a bony block against inferior humeral translation
Static Stabilization of the GH Joint in Neutral Position
- Supraspinatus activity is recruited when passive forces are inadequate for static stabilization
- Supraspinatus tendon attachments to the rotator interval capsule contribute to static stabilization
- Subscapularis may also provide support through its connections to the rotator interval
- Muscles with an upward-directed translatory force component (deltoid, supraspinatus, biceps brachii, triceps brachii) help with stability under extreme load
Mobility - Osteokinematics
- GH joint rotates in all 3 planes and has 3 degrees of freedom
- Primary rotational movements:
- Flexion and extension (sagittal plane around ML axis)
- Abduction and adduction (frontal plane around AP axis)
- Internal and external rotation (horizontal plane around the long axis of the humerus)
- Horizontal adduction and abduction occur at the GH joint
Dynamic Stabilization of the GH Joint - Dynamic Stabilizers
- Stabilization is a result of coordinated muscular action during movement
- Deltoid muscle is a prime mover for abduction and flexion
- Deltoid's superiorly directed force would cause humeral head impact with the coracoacromial arch if unopposed
- Rotator cuff muscles provide dynamic stabilization and reinforce the GH capsule (SITS: supraspinatus, infraspinatus, teres minor, subscapularis)
- Inferior translator components of these 3 muscles offset the superior translatory force of the deltoid muscle
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Description
This quiz explores the anatomy and functions of the acromioclavicular joint, including the ligaments that provide its stability and mobility. Learn about the roles of the coracoclavicular ligament and the impact on shoulder mechanics. Test your understanding of this crucial joint's structure and function.
