Shoulder And The Arm

Question 1

The scapula

Answer 1

The scapula (non-medically referred to as the ‘shoulder blade’) is classified as an irregular bone.

It articulates with the humerus at the glenohumeral joint, and with the clavicle at the acromioclavicular joint. In doing so, the scapula connects the upper limb to the trunk

The scapula is a triangular, flat bone, which serves as a site for attachment for seventeen different muscles!

The costal (anterior) surface of the scapula faces the ribcage. It contains a large concave depression over most of its surface, known as the subscapular fossa.

The subscapularis (rotator cuff muscle) originates from this fossa

The coracoid process arises from the superolateral surface of the scapula and projects anterolaterally. It is a hook-like projection, which lies just underneath the clavicle.

The pectoralis minor muscle inserts onto the coracoid process, and the coracobrachialis and the short head of the biceps brachii originate from it.

The lateral surface of the scapula is the site of the glenohumeral joint, and of various muscle attachments.

Question 2

bony landmarks/site of origins/ articulations present in the scapula

Answer 2

The important bony landmarks of the lateral surface of the scapula are:

Question 3

Fractures of the scapula

Answer 3

Fractures of the scapula are relatively uncommon, and if they do occur, they are an indication of severe chest trauma.

They are frequently seen in high

Question 4

Clavicle

Answer 4

The clavicle (referred to non-medically as the collarbone) extends between the manubrium of the sternum and the acromion of the scapula

The clavicle has three main functions. It:

Question 5

Acromioclavicular joint

Answer 5

The acromioclavicular (AC) joint is a plane-type synovial joint. It is located where the lateral end of the clavicle articulates with the acromion of the scapula.

The AC joint can be palpated during a shoulder examination 2-3cm medially from the ‘tip’ of the shoulder (which is formed by the end of the acromion).

The AC joint has two atypical features:

Question 6

Sternoclavicular joint

Answer 6

The sternoclavicular joint is a synovial joint between the clavicle and the manubrium of the sternum.

It is the only attachment of the upper limb to the axial skeleton so is very strong.

Unusually, despite its strength, it is a very mobile joint.

The sternoclavicular joint consists of the sternal end of the clavicle, the manubrium of the sternum, and the upper medial part of the first costal cartilage.

It is a saddle-type synovial joint. However, like the acromioclavicular joint, the articular surfaces of the sternoclavicular joint are covered with fibrocartilage (as opposed to the hyaline cartilage that is present in the majority of synovial joints).

The sternoclavicular joint is also separated into two compartments by a fibrocartilaginous articular disc.

This allows the clavicle and the manubrium to slide over each other more freely, allowing for the rotation and movement in a third axis (rather than the two axes usually permitted by saddle-type joints).

The sternoclavicular joint has a large degree of mobility. There are several movements of the shoulder that also require movement at the sternoclavicular joint:

Question 7

The proximal humerus

Answer 7

The humerus is a long bone of the upper limb and extends from the shoulder to the elbow.

The proximal humerus articulates with the glenoid fossa (glenoid cavity) of the scapula, forming the glenohumeral joint.

Distally, at the elbow joint, the humerus articulates with the head of the radius and trochlear notch of the ulna.

The proximal humerus comprises a head, anatomical neck, surgical neck, greater and lesser tubercles and an intertubercular sulcus.

The humeral head faces medially, superiorly and posteriorly and is separated from the greater and lesser tubercles by the anatomical neck.

The greater tubercle is a rounded projection on the posterolateral aspect of the proximal humerus.

It serves as the site of insertion of three of the rotator cuff muscles: supraspinatus, infraspinatus and teres minor, which insert into the superior, middle and inferior facets respectively

The lesser tubercle is much smaller, and more medially located. It provides the insertion site for the last rotator cuff muscle: subscapularis.

Separating the two tubercles is a deep depression called the intertubercular sulcus (intertubercular groove).

The tendon of the long head of biceps brachii (here) emerges from the shoulder joint and runs through this groove.

The edges of the intertubercular sulcus are known as the lips.

Pectoralis major inserts onto the lateral lip, teres major onto the medial lip and latissimus dorsi onto the floor of the intertubercular sulcus.

The anatomical neck of the humerus is obliquely directed, forming an obtuse angle with the body of the humerus.

It is easiest to identify in the lower half of its circumference; in the upper half it is represented by a narrow groove separating the head of the humerus from the greater tubercle and the lesser tubercle.

The anatomical neck is the site of attachment of the articular capsule of the shoulder joint. It also marks the region of the epiphyseal growth plate during the growth in length of the humerus in childhood

The surgical neck of the humerus is a constriction below the tubercles of the greater tubercle and lesser tubercle and lies between the two tubercles and the shaft of the humerus.

It is much more frequently fractured than the anatomical neck of the humerus. A fracture in this area may cause damage to the axillary nerve and posterior circumflex humeral artery.

Question 8

Fracture of the surgical neck of the humerus

Answer 8

The surgical neck of the humerus is a frequent site of fracture; usually from blunt trauma to the shoulder or from falling on an outstretched hand.

The key neurovascular structures at risk here are the axillary nerve and posterior circumflex artery.

Axillary nerve damage will result in paralysis of the deltoid and teres minor muscles.
The patient will have difficulty performing abduction of the affected limb.

This nerve also innervates the skin over insertion of deltoid (regimental badge area), and sensation in this region will be impaired Image: Radiopaedia
(Remember Hilton’s Law).

Question 9

Shaft of the humerus

Answer 9

The shaft of the humerus has a circular cross-section proximally and is more flattened in cross-section distally.

On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the deltoid tuberosity.

The radial (or spiral) groove is a shallow depression that runs diagonally on posterior surface of the humerus at the level of the deltoid tuberosity.

The radial nerve and profunda brachii artery lie in this groove.

The following muscles attach to the humerus along its shaft:

Question 10

The shoulder

Answer 10

The shoulder girdle (pectoral girdle) consists of the clavicle and the scapula. These bones connect the arm to the axial skeleton.

The shoulder joint is technically known as the glenohumeral joint and represents the joint formed by the head of the humerus and the glenoid fossa of the scapula.

The other joints in the shoulder girdle are the sternoclavicular joint (articulation of sternum and clavicle, here) and the acromioclavicular joint (articulation of scapula and clavicle, here)

The scapulothoracic joint (the articulation of the scapula with the thoracic wall) is not a true joint.

The humeral head is larger than the glenoid fossa so this joint can be compared to a golf ball sitting on a tee

It is a ball-and-socket joint and is in many ways homologous to the hip joint.

However, the function required from the shoulder joint differs from that of the hip joint in that a large range of movement is required to position the hand in space, but it does not need to bear such a heavy load.

Therefore, the shoulder has evolved to provide great flexibility and mobility at the expense of stability. As such, it is the most mobile joint in the body.

The glenohumeral joint is a synovial joint and the head of the humerus is covered with hyaline cartilage. The glenoid fossa is a relatively shallow cartilage-lined socket in which the humeral head articulates.

The shallowness of the glenoid fossa facilitates motion and flexibility but also increases the risk of a dislocation of the shoulder joint.

To overcome this, there is an additional rim of fibrocartilaginous tissue around the edge of the glenoid cavity called the glenoid labrum. This is approximately 1cm in width; its function is to deepen the socket and reduce the risk of dislocation.

The joint capsule of the shoulder is relatively loose. Reinforcement is provided by the rotator cuff muscles, but the inferior aspect has no reinforcement so is the weakest part.

Question 11

Ligaments of the shoulder

Answer 11

Further reinforcement of the shoulder joint is provided by ligaments

There are three glenohumeral ligaments that are named according to their location; superior, middle and inferior.

These glenohumeral ligaments are all situated on the anterior aspect of the joint and act to reduce the risk of anterior dislocation (the most common direction of dislocation of the shoulder).

There are additional ligaments in the shoulder region.

Some provide stability: the conoid ligament and trapezoid ligament together form the coracoclavicular ligament, linking the coracoid process of the scapula with the clavicle.

The coracohumeral ligament attaches the coracoid process of the scapula to the greater tubercle of the humerus.

Other ligaments provide tunnels through which tendons can run without bowstringing whilst the muscle is in use.

The transverse humeral ligament creates a tunnel between the greater and lesser tuberosities of the humerus to allow passage of the long head of biceps.

The coraco-acromial ligament provides the ‘roof’ of the subacromial space, a tunnel above the glenohumeral joint that allows passage of the supraspinatus tendon.

This ligament prevents superior dislocation of the humerus when a person falls onto their outstretched hand.

Question 12

Muscles of the shoulder region

Answer 12

The muscles of the shoulder can be divided into extrinsic muscles and intrinsic muscles.

The extrinsic muscles of the shoulder originate from the torso and insert onto the bones of the shoulder (clavicle, scapula or humerus).

The intrinsic muscles of the shoulder originate from the scapula and/or clavicle and insert onto the humerus.

Note: In addition to those muscles classed as the extrinsic and intrinsic muscles of the shoulder, there are other muscles that act on the shoulder joint e.g. the muscles of the pectoral region and the arm. These are described in other sections of this textbook.

Question 13

Trapezius

Answer 13

The trapezius is a broad, flat, superficial, triangular muscle and is the most superficial of all the back muscles.

It originates from the external occipital protuberance of the skull, the nuchal ligament and the spinous processes of C7-T12.

The muscle fibres insert onto the clavicle, acromion and the spine of the scapula

Innervation: The motor innervation to trapezius is from the spinal accessory nerve
Trapezius also receives proprioceptor (position-sense) fibres from the C3 and C4 spinal nerves.

Actions: The upper fibres of the trapezius elevate the scapula and rotate it during abduction of the arm above 90°. The middle fibres of trapezius retract the scapula and the lower fibres pull the scapula inferiorly.

To test the power of the trapezius muscle clinically, you can ask the patient to shrug their shoulders whilst you attempt to push them back down.

Question 14

Latissimus Dorsi

Answer 14

The latissimus dorsi covers a wide area on the lower back. At their origin, the superior fibres of latissimus dorsi lie deep to the inferior fibres of trapezius.

Latissimus dorsi has a broad superficial origin, arising from the spinous processes of T6-T12, the iliac crest, thoracolumbar fascia (a large sheet of deep fascia enclosing the intrinsic muscles of the back e.g. quadratus lumborum) and the inferior three ribs.

The fibres converge into a tendon that inserts into the intertubercular sulcus of the humerus

Actions: Latissimus dorsi extends, adducts and medially rotates the upper limb.

Question 15

Lavator Scapuale

Answer 15

Levator scapulae is a small deep strap-like muscle. It originates from the transverse processes of the C1-C4 vertebrae and inserts on the medial border of the scapula.

It lies deep to the trapezius muscle and superior to rhomboid minor

Innervation: Dorsal scapular nerve

Actions: Levator scapulae elevates the scapula.

Question 16

Rhomboid Minor

Answer 16

Rhomboid minor originates from the spinous processes of the C7-T1 vertebrae.

It inserts onto the medial border of the scapula, at the level of the spine of the scapula.

Innervation: Dorsal scapular nerve.

Actions: Rhomboid minor retracts the scapula and rotates the medial border, such that the glenoid fossa is rotated inferiorly.

It therefore helps return it to its anatomical position following previous abduction of the arm above 90°.

Question 17

Rhomboid major

Answer 17

Rhomboid major originates from the spinous processes of the T2-T5 vertebrae.

It inserts onto the medial border of the scapula, between the scapular spine and the inferior angle of the scapula.

Innervation: Dorsal scapular nerve.

Actions: Rhomboid major retracts the scapula and rotates the medial border, such that the glenoid fossa is rotated inferiorly.

It therefore helps return it to its anatomical position following previous abduction of the arm above 90°.

Question 18

Deltoid

Answer 18

The deltoid muscle is a triangular muscle, shaped like the Greek letter delta: Δ.

It can be divided functionally into anterior, middle and posterior parts.

Deltoid originates from the anterior border and upper surface of the lateral third of the clavicle, and from the acromion and spine of the scapula.

It inserts into the deltoid tuberosity on the lateral surface of the humerus

Innervation: Axillary nerve (C5,6 from the posterior cord of the brachial plexus)

Actions:

Question 19

Teres major

Answer 19

The teres major muscle forms the inferior border of the quadrangular space – the ‘gap’ that the axillary nerve and posterior circumflex humeral artery pass through to reach the posterior scapula region

Teres major originates from the posterior surface of the inferior angle of the scapula.

It passes anterior to the long head of triceps to insert onto the medial lip of the intertubercular groove of the humerus

Actions: Teres major adducts and extends the arm at the shoulder and also medially (internally) rotates the arm.

(Note: it is a medial (internal) rotator because it passes anterolaterally from its origin to insert onto the anteromedial surface of the humerus at the medial lip of the intertubercular groove;
contraction of the muscle fibres therefore rotates the insertion point on the humerus posteromedially, so rotates the shaft of the humerus medially).

Question 20

Supraspinatus

Answer 20

One of the rotator cuff muscles

Supraspinatus originates from the supraspinous fossa of the scapula and inserts onto the greater tubercle of the humerus

Innervation: Suprascapular nerve (This is a branch of the upper trunk of the brachial plexus with root values C5,6; you will recall that the myotome for abduction of the shoulder is C5)

Actions: Supraspinatus abducts the arm from 0-15°, and assists deltoid in abducting the arm from 15-90°.

Question 21

Infraspinatus

Answer 21

Infraspinatus originates from the infraspinous fossa of the scapula and inserts onto the greater tubercle of the humerus, between the insertions of supraspinatus and teres minor

Innervation: Suprascapular nerve.

Action: Infraspinatus laterally rotates the arm.

Question 22

Subscapularis

Answer 22

Subscapularis originates from the subscapular fossa, which is on the costal surface of the scapula

It inserts onto the lesser tubercle of the humerus.

Innervation: Upper and lower subscapular nerves (For interest only: from the posterior cord of the brachial plexus).

Actions: Subscapularis medially (internally) rotates the arm.

Question 23

Teres minor

Answer 23

Teres minor originates from the posterior surface of the scapula, adjacent to the lateral border

It inserts onto the greater tubercle of the humerus inferior to the insertion of infraspinatus

Innervation: Axillary nerve (C5,6 from the posterior cord of the brachial plexus; Note the axillary nerve also supplies the deltoid muscle).

Actions: Teres minor laterally rotates the arm.

Question 24

Anterior compartment of the arm

Answer 24

The three muscles of the anterior compartment of the arm, biceps brachii, coracobrachialis and brachialis, are all innervated by the musculocutaneous nerve.

The arterial supply to the anterior compartment of the upper arm is via muscular branches of the brachial artery.

Muscles in the anterior compartment of the arm (innervated by thmusculocutaneous nerve) = Mnemonic BBC:
B = Biceps brachii
B = Brachialis
C = Coracobrachialis

Question 25

Biceps Brachii

Answer 25

The biceps brachii is a two-headed muscle. Although the majority of the muscle mass is located anteriorly to the humerus, it has no attachment to the bone itself.

The long head of biceps brachii originates from the supraglenoid tubercle of the scapula and passes through the shoulder joint, inside the joint capsule.

The short head of biceps originates from the coracoid process of the scapula.

Both heads unite to form a single muscle belly distally. Biceps brachii then inserts into the radial tuberosity via the biceps tendon and also into the deep fascia of the forearm via the bicipital aponeurosis

The bicipital aponeurosis is a thick fascial band that originates close to the musculotendinous junction of the biceps, forms the roof of the cubital fossa and ends by blending with the deep fascia at the ulnar border of the anterior forearm.

Action: Biceps brachii is a strong supinator of the forearm at the radioulnar joints, It also flexes the arm at the elbow and the shoulder joints.

One way of remembering this is that these movements are used when opening a bottle of wine with a corkscrew: the biceps first unscrews the cork (supination) then pulls it out (flexion).

Innervation: Musculocutaneous nerve (C5-7 from the lateral cord of the brachial plexus)
The biceps tendon reflex tests spinal cord segment C6 (figure 7.34) because this myotome is predominantly responsible for elbow flexion and for supination.

Question 26

Rupture of the Biceps tendon

Answer 26

The long head of the biceps may rupture near to its scapular origin, most commonly in patients over the age of 50 years following quite minimal trauma.

Typically, the patient reports that they heard something “snap” in the shoulder whilst lifting. Characteristically, flexion of the arm at the elbow produces a firm lump in the lower part of the arm - this is the unopposed contracted muscle belly of the biceps and is called the ‘Popeye sign’.

The patient will not notice much weakness in the upper limb because the action of the brachialis (flexion) and supinator (supination) muscles is intact, so management is usually conservative.
In weightlifters, the distal tendon of the biceps sometimes snaps near to its insertion instead.

Question 27

Coracobrachialis

Answer 27

The coracobrachialis muscle lies deep to the short head of biceps brachii in the arm

Coracobrachialis originates from the coracoid process of the scapula.

The muscle passes through the axilla and inserts onto the medial side of the humeral shaft, at the same level as the deltoid tubercle

Action: Coracobrachialis flexes the arm at the shoulder and is a weak adductor of the arm.

Innervation: Musculocutaneous nerve (C5-7 from the lateral cord of the brachial plexus).

Question 28

Brachialis

Answer 28

The brachialis muscle lies deep to the biceps brachii in the distal half of the arm. It forms the floor of the cubital fossa

Brachialis originates from the anterior surface of the distal half of the humeral shaft and inserts onto the coronoid process of the ulna and the ulnar tuberosity, just distal to the elbow joint

Action: Brachialis flexes the forearm at the elbow

Innervation: Musculocutaneous nerve (C5-7), with contributions from the radial nerve (C5 and C6 fibres).)

Question 29

Posterior compartment of the arm

Answer 29

The posterior compartment of the arm contains the triceps brachii muscle, which has three heads.

The medial head lies deeper than the lateral and long heads, which cover it.

The arterial supply to the posterior compartment of the upper arm is via the profunda brachii artery.

Question 30

Triceps brachii

Answer 30

The origins of the three heads of triceps brachii are as follows:

Question 31

The quadrangular and triangular spaces and triangular interval

Answer 31

The quadrangular and triangular spaces and the triangular interval are passageways between the muscles of the shoulder region.

The quadrangular space is clinically important because it is the route via which the axillary nerve and posterior circumflex humeral artery (and vein) enter the posterior compartment of the arm.
It is bounded by

Question 32

Bursae around the shoulder joint

Answer 32

A bursa is a fluid filled sac that provides a cushion between a tendon and a bone (or ligament) to allow a smooth gliding action of the tendon.

The two bursae you need to be aware of at the shoulder are the subscapular bursa and the subacromial bursa:

The subacromial bursa lies under the acromion

It separates the supraspinatus tendon from the overlying coraco-acromial ligament, the acromion, the coracoid process and from the deep surface of the deltoid muscle.

It acts like a cushion, reducing friction as the supraspinatus tendon passes under these structures.

The subscapular bursa is located between the tendon of subscapularis and the neck of the scapula.

It protects the tendon of the subscapularis muscle as it passes inferior to the root of the coracoid process and over the neck of the scapula
There are other bursae in the shoulder region but you do not need to know about these for this MSK unit.

Question 33

The subacromial space

Answer 33

The space between the coraco-acromial arch (formed by the coracoid process, coraco-acromial ligament and acromion) and the head of the humerus, normally measures 1-1.5cm.

Packed into this space are:

Question 34

Abduction of the shoulder

Answer 34

Abduction of the shoulder is carried out by several different muscles.

The first 90° of abduction occurs at the glenohumeral joint. Of this:

Question 35

Adduction of the shoulder

Answer 35

Adduction of the shoulder is also carried out by several different muscles:

Question 36

Flexion of the shoulder

Answer 36

Flexion of the shoulder is carried out by several different muscles:

Question 37

Extension of the shoulder

Answer 37

Extension of the shoulder is carried out by:

Question 38

Internal (medial rotation of the shoulder)

Answer 38

Internal (medial) rotation of the shoulder is carried out by:

Question 39

External rotation of the shoulder

Answer 39

External rotation of the shoulder is carried out by:

Question 40

factors contributing to the stability of the shoulder joint (glenohumoral joint)

Answer 40

Static stabilisers (provide stability at rest):

Question 41

Neurovascular structures in the shoulder joint

Answer 41

When the subclavian artery crosses the lateral
border of the first rib to enter the axilla, it becomes known as the axillary artery.

The axillary artery passes behind the pectoralis minor muscle and at the level of the surgical neck of the humerus, gives off the anterior and posterior circumflex humeral arteries

These encircle the neck of the humerus to supply the shoulder region.

There is also an arterial anastomosis (connection between vessels) around the margin of the scapula.

The subscapular artery arises from the third part of the axillary artery to form part of this anastomosis, anastomosing with branches of the suprascapular artery and transverse cervical artery.

The arterial supply of the shoulder joint is derived from the anterior and posterior circumflex numeral arteries and the suprascapular artery

The axillary artery becomes the brachial artery at the inferior border of the teres major muscle

The brachial artery is a continuation of the axillary artery past the inferior border of the teres major muscle

It provides the main supply blood supply to the arm and forearm.
Immediately distal to the teres major, the brachial artery gives rise to the profunda brachii (deep brachial artery), which travels with the radial nerve in the radial (spiral) groove of the humerus and supplies the structures in the posterior compartment of the arm (e.g. triceps brachii).

The profunda brachii terminates by contributing to an anastomotic network around the elbow joint.

The brachial artery then descends in the anterior compartment of the arm. As it passes through the cubital fossa, underneath the brachialis muscle, the brachial artery terminates by bifurcating into the radial and ulnar arteries.

The brachial pulse is palpated in the cubital fossa, medial to the tendon of biceps brachii.

In the proximal arm, the median nerve lies immediately lateral to the brachial artery.

Distally, the median nerve crosses to the medial side of the brachial artery.

The brachial plexus passes inferomedial to the shoulder joint to enter the axilla.

The cords of the brachial plexus lie in close relationship with the axillary artery, and are named according to their anatomical relationship with the second part (middle section) of this artery
i.e. the medial cord is medial to the second part of the axillary artery, the lateral cord is lateral to it and the posterior cord is posterior.

Question 42

Anterior dislocated shoulder

Answer 42

Dislocations of the shoulder joint are a relatively common reason for attendance to the Emergency Department.

The patient’s shoulder will be visibly deformed and there may be visible swelling and/or bruising around the shoulder.

Movement of the shoulder will be severely restricted. 90-95% of dislocations are anterior (i.e. the head of the humerus sits anterior to the glenoid fossa).

The glenoid fossa is shallow.

Although the joint is strengthened on its superior, anterior and posterior aspects, it is weak at its inferior aspect.

The head of the humerus therefore usually dislocates anteroinferiorly, but then often displaces in an anterior direction (subcoracoid location = 60% of cases) due to the pull of the muscles and disruption of the anterior capsule and ligaments.

Alternatively, the head of the humerus may come to lie antero-inferior to the glenoid (subglenoid location = 30% of cases).

Both are types of anterior dislocation. The arm is held in a position of external rotation and slight abduction.

The first episode of anterior dislocation usually occurs when an individual has their arm positioned in abduction and external rotation (“hand behind head”), and an unexpected small further injury forces the arm a little further posteriorly, pushing the shoulder into an extreme position, such that the humeral head dislocates antero-inferiorly from the glenoid.

An alternative mechanism is a direct blow to the posterior shoulder.

The force of the humeral head popping out of the socket often causes part of the glenoid labrum to be torn off.

This is called a Bankart lesion or labral tear. Sometimes a small piece of bone can be torn off with the labrum.

When the humeral head is dislocated anteriorly, the tone of the infraspinatus and teres minor muscles means that the posterior aspect of the humeral head becomes jammed against the anterior lip of the glenoid fossa.

This can cause a dent (indentation fracture) in the posterolateral humeral head known as a Hill-Sachs lesion.

Approximately 50% of people aged under 40 years with anterior shoulder dislocation, and up to 80% of those with recurrent dislocations will have Hill-Sachs lesions.

These increase the risk of secondary osteoarthritis in the shoulder joint.

Question 43

Posterior shoulder dislocations

Answer 43

Posterior dislocations of the shoulder are far less common (2-4% of cases).

They tend to occur when there are violent muscle contractions due to an epileptic seizure, electrocution or a lightning strike; when there is a blow to the anterior shoulder; or when the arm is flexed across the body and pushed posteriorly.

Therefore, if you ever see a posterior dislocation, you should be thinking about the reason ‘why’ it happened.

Patients usually present with their arm internally rotated and adducted.

They demonstrate flattening / squaring of the shoulder with a prominent coracoid process. The arm cannot be externally rotated into the anatomical position.

A posterior dislocation of the shoulder can easily be missed on an X-ray as it looks ‘in joint’.

However, because the arm is internally-rotated, the projection of the humeral head onto the X-ray film changes to a more rounded shape – the

Question 44

Inferior shoulder dislocations

Answer 44

Inferior dislocations are even rarer (0.5%). After inferior dislocation, the head of the humerus sits inferior to the glenoid.

The mechanism is forceful traction on the arm when it is fully extended over the head, as may occur when grasping an object above the head to break a fall i.e. a hyperabduction injury.

Injuries associated with inferior dislocation include damage to nerves (60%), rotator cuff tears (80%), and injury to blood vessels (3%).

Question 45

Complications of shoulder dislocations

Answer 45

The most common complication of shoulder dislocation (in any direction) is recurrent dislocation due to damage to the stabilising tissues surrounding the shoulder (glenoid labrum, capsule, ligaments etc.).

The chance of further dislocation can be estimated at 60% but depends on age and activity level.

As we age, our tissues lose elasticity, so the risk of recurrent dislocation is approximately 90% in 20-year-olds, falling to only 10% in 40-year-olds.

Each dislocation results in further damage to the humeral head and glenoid, therefore it is unsurprising that the risk of osteoarthritis increases with the number of dislocations.

Damage to the axillary artery occurs in 1–2% of shoulder dislocations, more commonly in the older age group as their blood vessels are less elastic.

The patient may have a haematoma, absent pulses and/or a cool limb.

Nerve injuries are more common than arterial injuries, particularly injuries of the axillary nerve which occur in around 10–40% of shoulder dislocations.

The axillary nerve wraps around the neck of the humerus, and supplies the deltoid muscle and the skin overlying the insertion of deltoid (Apply Hilton’s law: the nerve supplying the muscle [deltoid] also supplies the skin overlying the insertion of the muscle [insertion of deltoid]).

This is known as the regimental badge area as it corresponds with where a shoulder badge would be worn on the sleeve of a jacket.

Most people with axillary nerve damage recover fully, as the symptoms resolve when the shoulder is reduced (i.e. put back in position).

Less commonly, dislocation of the shoulder may damage the cords of the brachial plexus or musculocutaneous nerve.

Significant fractures occur in around one quarter of shoulder dislocations, and are more common when there is a traumatic mechanism of injury, first-time dislocation, or the person is aged over 40.

Commonly affected bones include the head or greater tubercle of the humerus, the clavicle and the acromion.
Rotator cuff muscle tears can also occur in association with shoulder dislocation, most commonly in older people.

As described above, they are also a common complication of inferior dislocation in all age groups (80% of inferior dislocations are associated with a rotator cuff tear).

The integrity of the rotator cuff should always therefore be assessed as part of the follow-up of patients after reduction of a dislocated shoulder.

Question 46

Clavicle fractures

Answer 46

Clavicle fractures are common, accounting for 3-5% of all fractures, with a peak age in children and young adults.

The clavicle acts as a strut to brace the shoulder from the trunk (so the arm has freedom of motion) and transmits force from the upper limb to the axial skeleton.

It also provides protection to the brachial plexus, subclavian vessels and the apex of the lung.

80% of fractures occur in the middle third of the clavicle (mid-clavicular fracture).

Most result from falls onto the affected shoulder or onto the outstretched hand.

Most clavicle fractures are treated conservatively (i.e. without surgery), using a sling.

Some indications for surgical fixation include:

Question 47

Rotator cuff tears

Answer 47

A rotator cuff tear is a tear of one or more of the tendons of the four rotator cuff muscles of the shoulder (supraspinatus, infraspinatus, subscapularis and teres minor).

It is among the most common conditions affecting the shoulder and is frequently seen in both primary care and orthopaedic outpatients.

The rotator cuff is responsible for stabilising the glenohumeral joint, abducting, externally rotating and internally rotating the humerus. When the rotator cuff tendons become torn, these functions are compromised.

The tendons of the rotator cuff are torn much more frequently than the muscles and, of these, the supraspinatus tendon is the most frequently affected where it passes beneath the coracoacromial arch, tearing at the site of its insertion into the greater tubercle of the humerus.

Although acute tears of the rotator cuff can occur (e.g. following shoulder dislocation), most rotator cuff tears are chronic, resulting from extended use in combination with other factors such as poor biomechanics or muscular imbalance.

The most common cause is age-related degeneration. With age, the blood supply to the rotator cuff tendons decreases, impairing the body’s ability to repair minor injuries.

The principal theory is a degenerative-microtrauma model, which supposes that age-related tendon degeneration, compounded by chronic microtrauma, results in partial tendon tears that then develop into full rotator cuff tears.

Inflammatory cells are recruited and oxidative stress leads to tenocyte (tendon cell) apoptosis, leading to further degeneration, thus a ‘vicious circle’ is created.

Recurrent lifting and repetitive overhead activity are also risk factors (e.g. carpenters, painters), as are sports that involve repeated overhead motion (e.g. swimming, volleyball, tennis, weightlifting).

As you would expect, rotator cuff tears are more common in the shoulder of the dominant arm, but a tear in one shoulder signals an increased risk of a tear in the opposite shoulder.

Post-mortem studies have shown that many rotator cuff tears are asymptomatic. However, the most common presentation clinically is anterolateral shoulder pain, often radiating down the arm.

This may occur with activity, particularly shoulder activity above the horizontal position, but it may also be present at rest.

Patients experience pain in their shoulder when they lean on their elbow and push downwards (e.g. leaning on an armrest of a chair), as this pushes the head of the humerus superiorly and decreases the space between the humeral head and the coracoacromial arch.

They also experience pain in the shoulder when reaching forward (flexing the shoulder) e.g. to take a bottle of milk from the refrigerator.

Pain-restricted movement above the horizontal position may be present, as well as weakness of shoulder abduction.

The weakness is often only found on physical examination, as it is the pain that predominantly limits the patient’s activities and leads them to seek medical attention.

As well as the history and examination, MRI and ultrasound both have a role in the diagnosis.

The management may be conservative (rest, analgesia etc.) or operative. However, the investigation and management are beyond the scope of this unit and you do not need to learn any further detail than this.

Question 48

Impingement syndrome

Answer 48

Impingement syndrome occurs when the supraspinatus tendon impinges (rubs or catches) on the coraco-acromial arch, leading to irritation and inflammation.

The space between the head of the humerus and the coracoacromial arch is relatively small (1 - 1.5cm).

Impingement may be caused by anything that narrows this space further e.g. thickening of the coracoacromial ligament, inflammation of the supraspinatus tendon, subacromial osteophytes (in osteoarthritis).

When the shoulder is abducted or flexed, the space becomes narrowed further, resulting in symptoms of pain, weakness and reduced range of motion.

The pain is often worsened by shoulder overhead movement and may also occur at night, especially if the patient is lying on the affected shoulder.

The onset of the pain may be acute if it is due to an injury, or may be insidious (gradually increasing) if it is due to a gradual process such as osteophyte formation.

The pain is described as dull rather than sharp, and lingers for long periods of a time, making it hard to fall asleep at night.

Other symptoms can include a grinding or popping sensation during movement of the shoulder.

The most common form is impingement of supraspinatus tendon under the acromion during abduction of the shoulder.

This creates a ‘painful arc’ between 60 and 120 degrees of abduction (below 60°and above 120°, patients experience significantly less, or no, pain).

Patients often report pain on reaching upwards to brush their hair or to lift a food can from an overhead shelf. Treatment is directed at the underlying cause.

Question 49

Calcification supraspinatus tendiopathy

Answer 49

Calcific supraspinatus tendinopathy (historically ‘tendonitis’) is characterised by the presence of macroscopic deposits of hydroxyapatite (a crystalline form of calcium phosphate) in the tendon of supraspinatus.

It can occur in any tendon of the rotator cuff but is by far most commonly seen in supraspinatus.

It can present with acute or chronic pain, often aggravated by abducting or flexing the arm above the level of the shoulder, or by lying on the shoulder.

Mechanical symptoms may also occur due to the physical presence of a large deposit, leading to stiffness, a snapping sensation, catching, or reduced range of movement of the shoulder.

Calcific tendinopathy is believed to be multifactorial. One theory is that regional hypoxia leads to tenocytes being transformed into chondrocytes and laying down cartilage in the tendon.

Calcium deposits are then formed through a process resembling endochondral ossification.

Another theory involves ectopic bone formation from metaplasia of mesenchymal stem cells normally present in tendons into osteogenic cells.

The calcific deposits are visible on X-ray.

They are crystalline in their ‘resting phase’. However, they are eventually reabsorbed by phagocytes, and it is during this reabsorption stage that they tend to cause the most pain.

During the reabsorption stage they look macroscopically like ‘toothpaste’ and often appear ‘cloudy’ (i.e. less well-defined) on X- ray.

Treatment is initially conservative with rest and analgesia. Surgical treatment is sometimes required for persistent symptoms.

Question 50

Adhesive capsulitis

Answer 50

Adhesive capsulitis, typically referred to as ‘frozen shoulder’ is a painful and disabling disorder in which the capsule of the glenohumeral joint becomes inflamed and stiff, greatly restricting movement and causing chronic pain.

The pain is usually constant, worse at night and exacerbated by movement and cold weather.

The exact cause of frozen shoulder is unknown but there are many risk factors.

Some believe there may be autoimmune component to the disease, possibly triggered by localized trauma to the shoulder.

Risk factors include

Question 51

Osteoarthritis

Answer 51

Osteoarthritis can occur in the shoulder joint and has radiological features similar to osteoarthritis occurring in other joints.

Osteoarthritis of the shoulder usually affects people over 50 years of age and more commonly affects the acromioclavicular joint than the glenohumeral joint.

The treatment ladder for OA of the shoulder is very similar to that for osteoarthritis of the hip, and has been reiterated here to aid your revision:

Treatment initially involves activity modification (avoiding activities that precipitate symptoms), analgesia, and anti-inflammatories (NSAIDs).

Some patients report a benefit from taking nutritional supplements e.g. glucosamine and chondroitin sulfate.

Steroid injections can be performed into the joint to reduce swelling and thereby alleviate shoulder stiffness and pain.

Hyaluronic acid injections into the joint (viscosupplementation) may increase lubrication, although the evidence for this is limited.

Arthroscopy (keyhole surgery) can be performed to remove loose
pieces of damaged cartilage from the glenohumeral joint, but some patients will progress to hemiarthroplasty (replacement of
the humeral head) or total shoulder replacement (replacement of the humeral head and the glenoid)