Shoulder Flashcards
What is the shoulder? Is it stable? Why?
- Glenohumeral joint
- It’s exceptionally mobile but very unstable
- There is poor bony congruence hence stability relies heavily on muscles, ligaments and brain to coordinate muscle patterns
- The humeral head sits within glenoid fossa, which is deepened by the glenoid labrum
- The capsule and Extracapsular ligaments function to restrain translation of humeral head within glenoid
- Muscle patterning moves the shoulder with force pairs where the agonist is the primary mover and the antagonist opposes it to prevent subluxation and dislocation
- When we move the shoulder, proprioceptive fibres in the capsule and muscles are activated and send signals to the brain
- The brain then sends a reflexive signal back to the antagonist, which will contract and bring the humeral head back to the centre of the glenoid
What is the glenohumeral joint?
-Surface area of humeral head is 4x larger than glenoid fossa hence humeral head and glenoid cavity have a small contact area hence easy to dislocate
Has glenoid labrum
- fibrocartilage
- triangular cross section
- 50% of glenohumeral depth is provided by labrum
- attachment to underlying bone are loose;superior portion is congruent with long head of biceps brachii tendon
What are the features of the proximal humerus?
- Head articulates with glenoid fossa
- Anatomical neck
- Surgical neck (axillary nerve and posterior circumflex arteries are here)
- Greater tubercle (lateral)
- Smaller tubercle (medial)
- Intertubercular groove (bicipital groove)
- Deltoid tuberosity
- Spiral groove (radial nerve and profunda brachi are here)
What are the movements of the shoulder?
- Flexion-extension
- Abduction-addiction
- Internal and external rotation
-Occurs in sagittal and coronal plane
Flexion = 167-171 degrees Extension = 45-60 degrees
What is the anatomy of the clavicle?
- S shaped double curve
- Protects underlying brachial plexus and vascular structure
- Elevates with upper limb elevation
- Transmit forces
Sternal end
- impression for costoclavicular ligament
- there are anterior and posterior costoclavicular ligaments which is attached to 1st rib costal cartilage to anterior and posterior aspects of clavicle. Resists superior clavicle displacement and anterior/posterior translation
Acromium end
- Conoid tubercle = for conoid ligament (medial aspect of coracoclavicular ligament)
- Trapezoid line = for trapezoid ligament (lateral aspect of coracoclavicular ligament)
What is costoclavicular ligament?
- Anterior and posterior
- Attached to 1st rib costal cartilage to anterior and posterior part of clavicle
- Resists super displacement
- Limits anterior and posterior translation
What are the conoid ligament and trapezoid ligament (coracoclavicular ligament)?
-Support scapula and stabilise against thorax
Conoid ligament:
- Runs from coracoid process to Conoid tubercle
- Restrains axial rotation and posterior translation of clavicle
Trapezoid ligament:
- Runs from coracoid process to trapezoid line
- Resists axial compression around a horizontal axis
What are the clavicular joints?
- Sternoclavicular joint: between sternal end of clavicle and manubrium
- Acromioclavicular joint: between acromium and acromial end clavicle
What is the sternoclavicular joint?
- Saddle shaped synovial joint
- Articular surfaces are covered by fibrocartilage
- Allows clavicle and sternum to slide over allowing rotation and movement
- Only bony connection of upper limb to thorax
- 4 degrees of clavicular rotation occurs for every 10 degrees of arm elevation at this joint
- Permits anterior, posterior, vertical movement and limited rotation
Ligaments involved
- Interclaviclar ligament = spans gap between sternal ends of each clavicle
- Costoclavicular ligament = anterior and posterior. From costal cartilage of 1st rib to anterior and posterior aspect of clavicle. Resists superior clavicle displacement; limits anterior and posterior translation
- Capsular ligament = forms anterior and posterior sternoclavicular ligaments. Stabilises the joint and prohibits excess displacement
What movement occur at the sternoclavicular joint?
- Elevation (shrugging, abduction at 90 degrees’
- Depression (drooping, extending shoulder behind body)
- Protraction and retraction
- Rotation
What is the acromioclavicular joint?
- Planar synovial joint
- May rotate up to 35 degrees at maximal shoulder abduction
- Both aspects of joint is covered with fibrocartilage
- Joint slopes infero-medially causing the clavicle to override acromium
- Allows axial rotation
- No muscles directly act at this joint so supported by scapulothoracic articulations
Ligaments: They prevent displacement
-Acromioclavicular ligaments = covers joint capsule. Restrains axial rotation and posterior translation of clavicle
-Coracoclavicular ligaments = Conoid and trapezoid ligament.
Conoid ligament: restrains axial rotation and posterior translation
Trapezoid ligament: resists axial compression around horizontal axis
-Coracoacromial ligament = confers stability to unstable joint
What are the ligaments of the sternoclavicular joint and acromioclavicular joint?
Sternoclavicular joint:
- Interclavicular ligament
- Costoclavicular ligament (anterior and posterior)
- Capsule ligament (sternoclavicular ligaments - anterior and posterior)
Acromioclavicular joint:
- Acromioclavicular ligament (covers joint capsule)
- Coracoclavicular ligament (Conoid and trapezoid)
- Coracoacromial ligament
What is fibrous capsule?
- Loose outerfibrous layer
- Inner synovial membrane (secretes synovial fluid which fills the joint capsule)
- Allows joint laxity and range of motion
Attachment points
- Glenoid labrum
- Anatomical neck
- Base coracoid process
Tightens during abduction, adduction, external and internal rotation
Posterior capsule:
-secondary restraint to anterior dislocation —> stabilises structure
What are the glenohumeral ligaments?
- Coracohumeral ligament
2. Glenohumeral ligament
What is the coracohumeral ligament?
- Reinforces superior aspect of capsule
- Prevents inferior displacement of humerus
- More important in individuals with less developed superior glenohumeral ligament
What is the glenohumeral joint?
Superior:
- Only well developed in 50% of people.
- Main restraint to inferior translation with arm in adductor position
Middle:
- Absent in 30% of shoulders
- Secondary restraint to inferior translation in abducted and externally rotated position
- Restrains anterior translation
Inferior:
- Has anterior band, posterior compartment and axillary pouch
- Anterior band = tightens in abduction and external rotation
- Posterior component = tightens with abduction and internal rotation
- Axillary pouch = allows abduction, flexion and extension
Inferior band limits:
- anterior translation
- posterior translation
- inferior translation
What are the important muscles here?
Outermost layer:
- Deltoid (anterior, middle and posterior fibres)
- Pec major (sternoclavicular head and clavicular head)
- Pec minor (scapular stabiliser)
Innermost layer:
-Rotator cuffs (infraspinatus, supraspinatus, subscapularis, teres minor)