Week 1 - Shoulder joint and girdle Flashcards
Describe the acromioclavicular joint
Synovial and small
Limited movement as there are no specific muscles for movement at this joint
What is the main joint of the shoulder girdle?
Sternoclavicular joint
Describe the sternoclavicular joint
Mismatched surfaces: broad clavicular surface, narrow sternal surface
Has an intra-articular disc
Strong ligaments associated with it - costoclavicular
Describe the glenohumeral (scapulohumeral) joint
Synovial ball and socket joint
Multi-axial
High mobility, compromises stability
Subject to intense wear and tear
What rims the glenoidal labrum?
White fibrocartilage, thinner than normal articular cartilage
Describe the glenohumeral joint capsule when the arm is in a resting position
Inferior and anterior portions are lax, superior portion is taut
Inferior is loose because the capsular attachment of the joint is far away from the articular margin of the humerus, but is close to the glenoid
What reinforces the anterior portion of the glenohumeral joint capsule?
The superior, middle and inferior glenohumeral ligaments, which form a Z-shaped pattern on the capsule
These are intracapsular ligaments
Which muscles support the GH joint capsule?
The rotator cuff muscles, supporting it superiorly, posteriorly and anteriorly
Where are the attachments of the GH joint capsule?
Glenoid - just outside the labrum
Humerus - superiorly is close to articular margin, interiorly is 1cm below margin
On which side is the GH joint vulnerable?
The inferior side
What four things supply stability to the GH joint?
Coracoacromial arch
Rotator cuff (dynamic stability)
Coraco-clavicular ligament
Tendon of biceps
What makes up the coracoacromial arch?
Acromion + coraco-acromial ligament + coracoid process
What four muscles make up the rotator cuff?
Subscapulaaris, infraspinatus, supraspinatus and Teres minor
How does the subscapularis move the humerus?
Rotates inwards
How do the infraspinatus and teres minor move the humerus?
Rotate it outwards
How do the rotator cuff muscles provide dynamic stability to the GH joint?
The joint capsule has sensory nerves, which are linked directly to the RC muscles via A-alpha nerve fibres. These carry any stretch from the capsule of ligament almost instantaneously, providing dynamic stability without compromising movement
What connects the coracoid process to the clavicle? Why is this important?
Two very strong ligaments called the coraco-clavicular ligaments. These are very thick
Important because acromioclavicular joint isn’t very strong - these ligaments transfer weight from the humerus to the clavicle
What are two important bursae in the GH joint?
Subacromial-subdeltoid bursa, the biggest one which is commonly inflamed
Subscapula bursae, found between the muscle/tendon and the scapula. Commonly communicates with joint synovial cavity through a hole in the cavity. This also increases chance of infection
Describe flexion and extension of the arm
In a sagittal plane, the arm moves forwards in flexion, and backwards in extension
Which large muscle is able to abduct the GH joint? Why?
The deltoid
It’s the only large muscle lateral to the joint. The others are medial and so adduct it
How can the Pec major move the GH joint?
Adduct, flex and rotate the joint
What are the four main flexors of the shoulder?
Pec major
Anterior deltoid
Subscapularis
Bicep brachii
–> any flexor anterior to the joint
How would you test whether Pec major is working?
Examine adduction
What is the most powerful extensor of the shoulder? What are some other extensors?
The Latissimus dorsi
Teres major, posterior deltoid, infraspinatus and teres minor are extensors as they are posterior to the joint
How do the lats move the shoulder joint?
Extensorly, nad adduct it, as they come from the medial side, attaching to the front of the humerus, like the pec major
Which part of the deltoid is an abductor of the shoulder joint?
The part on the acromion - middle region, lateral to the joint, which is also the thickest part
This abduction is also limited by bony factors
Which muscle initiates abduction of the shoulder?
The supraspinatus - only once humerus is at a certain angle does the deltoid take over
How would you test paralysis of the supraspinatus?
Whether the patient can abduct the shoulder while standing upright. If paralysed they’ll need to lean to the side to create the appropriate angle for the deltoid to start abduction
Which parts of the shoulder are involved in abduction?
Glenohumeral
Humerus
Pectoral girdle
Scapula and clavicle also rotate once glenohumeral joint has reached limit of movement (at the top)
What are the two major muscles involved in glenohumeral adduction?
Pec major and Lat
Anterior and posterior deltoid also plays a role
How do you tell if a muscle is a medial rotator?
If it’s in front of the joint i.e. pec major, Lat, subscapuaris anterior deltoid and T major
What are some lateral rotators of the shoulder?
Infraspinatus, teres minor
Infra is the major one
How do the trap muscles move the scapula?
Pull it in (retraction) and up (elevation)
Levator scapulae helps with elevation
What does girdle-glenohumeral harmony refer to?
Glenohumeral abduction is limited to 90 degrees, further abduction is accompanied by girdle movement, largely at the SC joint, though there’s some at the AC joint
