Describe the Trapezius
- Direct attachment of pectoral girdle to trunk
- Act on scapulothoracic joint
- Innervation: spinal accessory nerve (CNXI) and C3, C4 spinal nerves (pain and proprioceptive fibres)
-Divided into 3 parts: superior part elevates scapula (shrugging), middle part retracts scapula (squaring shoulder), inferior part depresses scapula
-Test trapezius by asking patient to shrug shoulder against resistance
How does the trapezius rotate the scapula?
Superior and inferior parts of trapezius act together to rotate scapula upwards and outwards on chest wall (elevating Glenoid cavity)
Serratus anterior muscle also assists in upward rotation of the scapula.
Scapular rotation is responsible for abduction of arm above horizontal (90 degrees)
Describe the Latissimus Dorsi
Wide origin, narrow insertion, fan-shaped
Powerful adductor of arm (climber's muscle) and extends arm at shoulder joint, medial rotator innervation:
Thoracodorsal nerve (C7, C6, C8 from posterior cord of the brachial plexus)
Describe the Levator Scapulae
Rotates scapula depressing Glenoid cavity
Describe Rhomboids Major and Minor
2 flat muscles with parallel fibres
Retracts scapula, rotates scapula, depresses Glenoid cavity, fixes scapula to thoracic wall
Innervation: dorsal scapular nerve (C4, C5)
Anterior fibres (Clavicular) - flexion of arm at shoulder joint
Middle fibres (Acromial) - abducts arm from 15-90
Posterior fibres (Spine of Scapula) - extends arm at shoulder joint, lateral rotation
Nerve supply: axillary nerve C5, C6
Describe the Teres Major
Adducts arm and medial rotation
Helps extend the arm from the flexed position
Lower subscapular nerve (C5, C6)
Describe the Shoulder Joint
Synovial joint of ball and socket
AKA gleno-humeral joint
Movement occurs at both glenohumeral and in abduction movement in scapulothoracic joints as well
Greatest range of movement of all joints but it is the most commonly disclosed joint.
Mobility is achieved at the cost of stability.
Why is the Shoulder Joint unstable?
Glenoid cavity is shallow
Disproportion of articular surfaces - the Glenoid cavity accepts little more than a third of the large, round humeral head
Multi planar movements
Lax capsule: loose fibrous layer of the joint capsule surrounding the joint
How is stability of the shoulder joint achieved?
Rotator cuff muscles (most important)
- Glenoid labrum deepens the Glenoid cavity
Describe the synovial membrane around the shoulder joint
Lines the capsule and bone up to the edge of the articulating surfaces,
A tubular sleeve of synovium reflected back around the biceps long head tendon (which lies within the joint) like a tube
The synovium and joint capsule is continuous with subscapular bursa through a gap in the capsule.
What are the intracapsular ligaments of the shoulder joint?
3 glenohumeral ligaments (superior, middle, inferior)
Describe the glenohumeral ligaments
3 fibrous bands that reinforce the anterior part of the joint capsule
Radiate from the Glenoid labrum at the supraglenoid fossa and blend display with the fibrous layer of the capsule as it is attached to the anatomical neck of the humerus.
Describe the coracohumeral ligament
Strong broad band that passes from the base of the CORACOID process to the anterior aspect of the greater tubercle of the humerus
Strengthens joint capsule superiorly
What are the extracapsular ligaments of the shoulder joint?
Describe the Transverse Humeral Ligament
Broad fibrous band that runs obliquely from greater to lesser tubercle, bridging over the intertubulcular groove.
It holds the synovial sheath and long biceps head tendon in place during movement - maintains stability.
Describe the Coracoacrmial Arch
Strong osseoligamentous structure formed by the acromion, CORACOID process and the coraco-Acromial ligament spanning between them.
Structure overlies humeral head
Prevents upper/superior displacement of humerus from Glenoid cavity
Supports joint superiorly
It is so strong that a forceful superior thrust of the humerus will not fracture it; the humeral shaft or clavicle fractures first.
How the Rotator Cuff Muscles stabilize the shoulder joint?
Hold the head of the humerus in the Glenoid cavity
Tendons blend with each other as they approach the humeral head to form a cuff which also fuses with capsule and strengthens it
Supraspinatus tendon is separated from the coracoacromial arch by subacromial bursa
Support joint anteriorly, posteriorly and superiorly.
What is the space between the acromion and head of humerus?
About 1-1.5 cm
Interposed in this space are: subacromial bursa, rotator cuff tendons, capsule, tendon of long head of biceps
What are the other muscles stabilising the shoulder joint?
Long head of biceps
Long head of triceps
Describe the subtendinous bursa of subscapularis
Facilitates movement of tendon of subscapularis muscle over scapula - protects tendon where it passes inferior to the root of the CORACOID process and over the neck of the scapula
Communicates with the joint cavity
Describe the subacromial bursa
Facilitates movement of supraspinatus tendon under the coracoacromial arch and deltoid muscle over the shoulder joint capsule and the greater tubercle of humerus.
Inflammation of bursa - subacromial bursitis - causes pain on abduction of the arm between 50 and 130 degrees ('painful arc syndrome'
What are the movements of the shoulder joint and muscles that produce them?
Flexion: Pec Major (Clavicular head), anterior fibres of deltoid, coracobrachialis and biceps brachii
Extension: posterior fibres of deltoid, Latissimus dorsi and Teres Major Abduction: Supraspinatus, Deltoid, Trapezius and Serratus Anterior (above 90 by rotating scapula)
Adduction: pec major, latissimus dorsi, teres major, long head of triceps brachii (+gravity in upright position)
Medial rotation: subscapularis, teres major, pec major, lat dorsi
Lateral rotation: infraspinatus and teres minor
Resisting downward dislocation (shunt muscles): deltoid, long head of triceps brachii, coracobrachialis, short head of biceps brachii
Describe the neurovascular supply to shoulder joint
Anterior and posterior circumflex humeral arteries and suprascapular artery
Suprascapular, axillary and lateral pectoral nerves from the brachial plexus
Which part of the shoulder joint is least supported?
Describe a dislocation of Glenohumeral joint
Dislocation in inferior direction
Usually caused by trauma on a fully abducted arm
Clinically defined as anterior due to pull of powerful adductors - humeral head comes to lie below the CORACOID process
Capsule and rotator cuff may tear and poor healing may occur leading to recurrent dislocation
Axillary nerve is most likely to be damaged --> paralysis of deltoid muscle loss of sensation (regimental badge area)
Posterior dislocations are rare.
What are the rotator cuff problems?
Tendons rubbing under coracoacromial arch cause irritation and inflammation of the rotator cuff tendons/subacromial bursa.
Leads to subacromial bursitis (+/- calcification), supraspinatus tendinitis (+/- calcification), rotator cuff injury and degeneration and rupture of tendons.
What are the predisposing factors (a combination of factors may be present)?
Repetitive overuse sporting activites (racquet sports, swimming) and work involving overhead use of arms e.g. painting a ceiling
In older people, degenerative changes in tendons
Avascularity of supraspinatus tendon
Slight differences in anatomy may may impingement more likely
What is Painful Arc Syndrome?
On abduction of the arm, pain experienced during 50-130 degrees of abduction.
Due to impingement of inflamed rotator cuff tendons or inflamed subacromial bursa between acromion and head of humerus.
What can repetitive use of the rotator cuff muscles lead to?
Allows the humeral head and rotator cuff to impinge on the coraco-Acromial arch, producing irritation of the arch and inflammation of the rotator cuff.
As a result degenerative tendinitis of the rotator cuff develops.
Attrition of the supraspinatus tendon may occur.
A fall on the shoulder may also tear a previously degenerated musculotendinous rotator cuff. What might have happened?
The intracapsular part of the tendon of the long head of the biceps brachii becomes frayed (even worn away) leaving it adherent to the intertubulcular space.
As a result shoulder stiffness occurs.
What happens when the Axillary nerve is damaged e.g. In a surgical neck of humerus fracture?
The rounded contour of the shoulder is flattened compared to the undamaged side.
This gives the shoulder a flattened appearance.
Loss of sensation may occur over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm (cutaneous branch of the axillary nerve)
Inability to abduct the arm to or above the horizontal level.
Describe a normal dislocation of the glenohumeral joint
Presence of the coraco-Acromial arch and support of the rotator cuff are effective in preventing upward dislocation so most dislocations occur in the inferior direction. However they are described clinically as anterior (or more rarely posterior) dislocations, indicating whether the humeral head has descended anterior or posterior to the infraglenoid tubercle and long head of the triceps. The head ends up lying anterior or posterior to the Glenoid cavity.
Describe an anterior dislocation of the glenohumeral joint in young adults, particularly athlete
Usually caused by excessive extension and lateral rotation of the humerus.
The head of the humerus is driven infero-anteriorly and the fibrous layer of the joint capsule and glenoid labrum may be stripped from the anterior aspect of the Glenoid cavity in the process.