Anatomy of shoulder Flashcards
List key surface markers of the anatomy of the shoulder
At the acromion, one can palpate the acromion itself, the acromioclavicular joint, and scapular spine (details on these features to follow).
Describe the clavicle
The clavicle is a modified, S-shaped long bone. It is convex medially and concave laterally (from the superior aspect).
It functions like a ‘strut’ to hold the shoulder girdle at a fixed distance from the chest wall. This helps to tense the shoulder muscles and provide it with a mechanical advantage.
It is important to note that the clavicle looks different superiorly and inferiorly.
The superior surface is more smooth.
The inferior surface has some processes. The image below shows the superior surface, and a diagram of the clavicle anteriorly, inferiorly and superiorly.
Describe the features of the clavicle
- sternal end or the medial end- viewable both superiorly and inferiorly. Note that the sternal end is more flat.
- acromial end or the lateral end- viewable both superiorly and inferiorly. The acromial end is more likely to be dislocated.
- body or shaft
- conoid tubercle
- trapezoid line
- impression for costoclavicular ligament
Describe the joints that the clavicle participates in
- acromioclavicular joint, formed by the acromial end of the clavicle and the acromion of the scapula. This joint is more likely to be dislocated.
- sternoclavicular joint, formed by the sternal end of the clavicle and the manubrium of the sternum. Dislocation is rare. It is more dangerous if posterior, as it may block off trachea and great vessels.
Clavicles can fracture along the shaft or become dislocated at either sternal or acromial ends. Clavicles are stabilised by ligaments, especially on the undersurface, 2.5cm medial from the lateral end. They are:
- conoid ligament
- trapezoid ligament, both of which attach to the coracoid process of the scapula.
Describe the key features of the scapula
Key features include:
- Body
- Spine, which terminates in the acromion laterally
- Coracoid process (coracobrachialis, pectoralis minor and short head of biceps originate here)
- Acromion, which is important because deltoid muscle attaches here, and rotator cuff muscles pass underneath. The narrowed subacromial space or downward sloping acromion pinches the cuff during elevation (see below for [[#Rotator cuff (mightily important)]])
- Glenoid cavity, articular surface with humerus
- Subscapular fossa
- Supraspinous fossa
- Infraspinous fossa
- Superior angle
- Inferior angle
- Medial border
- Lateral border
Describe the key features of the humerus (as it relates to shoulder)
- head
- anatomical neck, and surgical neck: note that these two terms are NOT synonymous. Anatomical neck rings around the articular surface, and separates rough humerus from smooth articular surface. Surgical neck is common site of fracture
-
greater and lesser tuberosity. Note that the greater tuberosity is more lateral to the lesser tuberosity when viewed anteriorly. The lesser tuberosity is not visible at all posteriorly.
- supraspinous, infraspinous and teres minor (off rotator cuff) insert onto greater tuberosity
- subscapularis inserts onto lesser tuberosity
-
bicipital groove: the long head of the biceps runs through here. Other muscles attach to the lateral lip, medial lip and floor
- lateral lip: pectoralis major
- medial lip: teres major
- floor: latissimus dorsi
- shaft
- deltoid tuberosity
- olecranon fossa
- coronoid fossa
- capitulum
- trochlea
- medial epicondyle
- lateral epicondyle
Describe the glenohumeral joint briefly
The head of the humerus forms the glenohumeral joint with the glenoid cavity of the (as well as the radiohumeral and humeroulnar joints, covered in lower limb lectures).
The glenohumeral joint is a ball-and-socket joint, and is thus capable of 360 degree motion (i.e. abduction and adduction, flexion and extension, internal and external rotation, elevation - which is a combination of flexion and rotation…and circumduction, which is not clinically relevant).
True or false: coronoid process is part of the scapula
Coracoid process of the scapula, and coronoid process of the ulna, are NOT the same structures.
Think, there is a c in scapula, and coracoid but not coronoid.
List the scapula stabilisers
only elaborate for two
- trapezius: shrugging, help stabilise and rotate scapula on the chest wall
- rhomboids major and minor: retract or rotate scapula
- levator scapulae: retract or rotate scapula
- serratus anterior: stabilises and minimally rotates the scapula
- latissimus dorsi: adduction and a little extension of humerus. Also minimally involved in rotating the shoulder. Good for grafting tendons
- teres major: adduction. Teres major extends, adducts and medially rotates the glenohumeral joint. It’s nerve supply is the lower subscapular nerve.
- pectoralis minor: stabiliser
List the key upper limb muscles
- deltoid
- triceps
- biceps
- pectoralis major
Describe deltoid and triceps
- deltoid
- attachments: the deltoid has a wide origin (lateral third anterior clavicle, acromion process, spine of scapula posterior border) inserted into deltoid tuberosity of humerus
- movements: abduction of the humerus – although it needs rotator cuff to function correctly (otherwise would simply elevate, rotator cuff holds humeral head down)
- innervation: axillary nerve, supplying it from posterior to anterior ^[susceptible to palsy with dislocation of humeral head as it wraps around it to supply deltoid]
- vascularisation: posterior circumflex humeral artery
- triceps
-
features
- attachments: inserts into posterior surface of olecranon process of ulna
- movements: elbow extension
- innervation: radial nerve
- vascularisation: deep brachial artery
-
features
Describe biceps and pectoralis major
- biceps
- features: long head (from glenoid labrum, arises intra-articularly), short head (from coracoid process)
- attachments: inserts into the radial tuberosity
- movements: elbow flexor and supinator
- innervation: musculocutaneous nerve
- vascularisation: muscular branches of brachial artery
- pectoralis major
- attachments: from the chest wall (clavicle and sternocostal) to the lateral lip of the bicipital groove
- movements: adduction and flexion of humerus (also medially rotates the glenohumeral joint). The clavicular head flexes the glenohumeral joint and the sternocostal head extends the glenohumeral joint from the flexed position
- innervation: lateral and medial pectoral nerves supplying the two heads
- vascularisation: several (thoraco-acromial - pectoral branch, internal thoracic artery — perforating branches…)
Other (less relevant) muscles of the upper arm include:
- coracobrachialis, from the coracoid process to the shaft.
- brachialis: which is somewhat involved in elbow flexion. Runs from the shaft and inserted into proximal ulna.
Describe the rotator cuff
There are four muscles that comprise the rotator cuff:
- subscapularis: which originates from the whole anterior surface of the scapula and inserts on the lesser tuberosity. Subscapularis* medially rotates the glenohumeral joint. It is suppliedby the upper & lower subscapular nerves.
- supraspinatus: originates from the supraspinatus fossa and inserts on the greater tuberosity. Supraspinatus* intitiates and assists deltoid with abduction of the glenohumeral joint. Innervated by the suprascapular nerve
- infraspinatus: originate from the infraspinatus fossa and inserts on the greater tuberosity. Infraspinatus* laterally rotates the glenohumeral joint.It is innervated by the suprascapular nerve.
- teres minor: originates from the inferior angle of the scapula and inserts on the greater tuberosity. Teres minor* laterally rotates the glenohumeral joint.It is innervated by the axillary nerve.
The tendons of supraspinatus, infraspinatus and teres minor blend together at the greater tuberosity.
All of the rotator cuff muscles function to stabilise the glenohumeral joint.
The rotator cuff muscles hold down the humeral head while the deltoid abducts the arm. Without the rotator cuff muscles the deltoid would pull the head upwards.
They are actually head depressors — holds down the head while the deltoid abducts the humerus.
The rotator cuff also has a role in internal and external rotation.
List the joints of the shoulder
| Acromioclavicular joint | Sternoclavicular joint | Glenohumeral joint | Scapulothoracic joint |
| —- | —- | —- | —- | —- |
| Articular surfaces | acromion and lateral end of clavicle | medial end of clavicle and sternum (manubrium/clavicular notch) | glenoid cavity and head of humerus | ribs of thoracic cage and posterior surface of scapula |
| Structural classification | synovial plane joint | synovial plane (saddle) | synovial - ball and socket | functional joint |
| Movements | gliding | gliding | In all planes: flexion and extension, abduction and adduction, intl and extl rotation (Elevation and circumduction) | intl and extl rotation (facilitated by swinging of inferior angle) <br></br><br></br>elevation and depression<br></br><br></br>protraction and retraction |
Subacromial space is sometimes included here
List and describe the components of glenohumeral stability
Glenohumeral stability
Glenohumeral stability is enforced by:
- muscles, which provide dynamic restraints, especially the rotator cuff (concavity compression and synchronous contraction), the biceps tendon and scapular stabilisers
- glenoid labrum: which deepens the glenoid, increasing the radius of curvature and stabilising the joint
- bony architecture: provides little help to stability, as the shoulder is primarily designed for movement (the glenoid is flat, humeral head is large)
- ligaments, especially the superior, middle and inferior glenohumeral ligaments, tighten with extremes of movement preventing further translation ^[capsular condensations best seen from within joint] (see also [[#Ligaments of the shoulder]])
- inferior glenohumeral ligament is the prime stabiliser of the shoulder
Instability can result from damage to the ligaments and labrum.
Treatment involves:
- strengthening
- physiotherapy
- (sometimes) surgery to reattach the damaged labrum and tighten the ligaments
