All that is The Shoulder

Trauma to the shoulder is common, although the type of injury varies considerably in different age groups. Clavicular fractures are common in childhood and early adulthood, glenohumeral dislocation and acromioclavicular disruption are frequent between the ages of 15 and 40 years, and fracture of the humeral head is often seen in elderly people. This chapter describes the features of these types of injury and a system of radiological interpretation to ensure that many of the subtle signs associated with them are not missed.

Important anatomical considerations

Adult

The shoulder consists of three bones and three joints. The acromion, coracoid process, and clavicle are linked by the shoulder ligaments. The coracoclavicular ligament is important as it is the main ligamentous attachment of the upper limb to the trunk. The acromioclavicular ligament is of secondary importance, but it is where radiographic evidence of injury is initially sought.

The inferior cortex of the most lateral aspect of the clavicle usually lies in same plane as the inferior cortex of the acromion. The distance from the coracoid process to the undersurface of the clavicle is 11-13 mm, with a difference in sides greater than 5 mm indicating rupture. The humeral head has two tuberosities and two necks; the surgical neck is the constricted portion distal to the level of the tuberosities. The neurovascular bundle (axillary artery and vein and median, ulna, and radial nerves) lies anterior to the glenohumeral joint and can be injured in anterior dislocation of the shoulder joint or in displaced fractures of the surgical neck.

Children and development

The three epiphyseal centres of the humeral head, greater tuberosity, and lesser tuberosity fuse with one another in the sixth year and with the shaft of the humerus in the 20th year.

The apophysis at the acromion appears at the age of 15 and is united within five years. The ossification centre at the interior angle of the scapula is generally seen between the ages of 15 and 25 years.

Common injury arising from trauma

Ligaments

Injury to the acromioclavicular/coracoclavicular ligament complex is classified according to the degree of disruption. Grade 1 injury is stable as the coracoclavicular ligament remains intact. As the injuring force increases, the acromioclavicular ligament is completely torn, with the coracoclavicular ligament either remaining intact or partially disrupted (grade 2). Stress views of the joint may be required to diagnose grade 1 and 2 injuries. Complete disruption of both acromioclavicular and coracoclavicular ligaments is termed grade 3.

Sternoclavicular disruption is uncommon but important because of associated vascular damage. This joint is not adequately seen in standard radiographs of the shoulder and specific views are therefore required if this injury is suspected clinically. Injury is usually suspected if chest radiography shows superior displacement of the medial end of the clavicle.

Glenohumeral dislocation

The shoulder is the most frequently dislocated joint of the body. Dislocations are usually clinically evident but radiography is needed to determine the direction of dislocation and the presence of any associated fracture or loose body. Dislocations are classified according to the position of the humeral head with respect to the glenoid fossa.

Anterior dislocations usually occur during excessive external rotation with the arm in abduction. Occasionally the injury is due to a direct posterolateral blow. Recurrent anterior dislocation is common and is indirectly related to age (80% in people aged below 20 years and 10% in those over 40).

About 60% of patients with anterior dislocations will also have compression fractures of the upper aspect of the humeral head, resulting in a flattened segment referred to as a hatchet deformity (Hill-Sachs). The fracture is caused by forceful impaction of the superolateral aspect of the humerus against the anterior or inferior rim of the glenoid fossa. It is often only seen in an axial or postreduction radiograph and is best seen with internal rotation of the arm. Anterior dislocation can also be associated with fractures of the greater tuberosity of the humerus (15%) and with fractures of the anterior rim of the glenoid fossa.

Direct posterior dislocation of the shoulder is uncommon but is a major diagnostic problem. Up to half are not recognised in the initial anteroposterior film. The posterior dislocation is typically associated with an anteromedial fracture of the humeral head. Simultaneous bilateral posterior dislocations are infrequent, occurring most commonly in patients with epilepsy.

Fractures

Fractures of the shoulder can occur at the proximal humerus or glenoid fossa and may be associated with dislocation (figs 6 and 8). Fractures can be classified as non-displaced, displaced, or impacted. Intra-articular fractures are often associated with joint effusions or lipohaemarthrosis.

Clavicle

Clavicular fractures are common and usually follow a fall on the shoulder or outstretched hand. About 80% of fractures occur at the mid-third of the clavicle and are transverse (fig 4). Typically there is overriding of the fracture with the distal fragment being displaced inferiorly by the weight of the upper limb. Fractures of the outer third of the clavicle are also usually transverse but non-displaced because of stabilisation from the acromioclavicular/coracoclavicular ligament complex. A raised proximal fragment suggests disruption of the coracoclavicular ligament.

Scapula

Fractures of the body of the scapula usually result from a direct crush-type injury and, with neck fractures, are the commonest injury of this bone. Fracture of the coracoid process is rare.

Non-traumatic lesions

Acute or severe shoulder pain and the painful arc syndrome are often due to inflammation of a periarticular bursa or tendon. Calcification of periarticular soft tissue or of the rotator cuff muscles is often associated with this acute inflammation. Pathological fractures of the humerus through benign or malignant bone lesions may occur spontaneously or with minimal trauma.

Types of view

The anteroposterior radiograph is the routine view performed in all patients (fig 2). The axial projection can be modified and taken with only minimal abduction and is therefore possible in most patients, even those with severe shoulder pain.

Occasionally the radiographer is unable to position the patient for a formal axial view. In these cases a through the chest lateral view (lateral transthoracic) may be taken, although this view is most useful for assessing alignment of humeral fractures and not dislocation. The axial view provides the most information and should be taken in all patients with trauma to the shoulder (fig 11).

Stress views

When the acromioclavicular ligament is completely disrupted but the coracoclavicular ligament remains intact, separation of the bones may not occur unless the joint is stressed. If such an injury is suspected specialised stress views should be taken with the patients holding weights. The non-injured shoulder should be examined in a similar manner to act as a control.

As with other radiographs the ABCs approach to interpretation is recommended.

Check the adequacy and quality of the radiograph

To take an anteroposterior shoulder view the patient is rotated slightly so that the glenohumeral joint is seen face on. The upper third of the humerus, outer half of the clavicle, and lateral aspects of the ribs should be visible.

Check alignment of bones

Firstly, check the humeral head is lying in the glenoid fossa. Then check the alignment of the acromioclavicular joint for disruption. Trace the inferior cortex of the clavicle across to the inferior cortex of the acromion. Remember partial or complete rupture of the acromioclavicular ligament can exist without disruption of the coracoclavicular ligament and can be detected only in stress views.

Check bone margins and density

Systematically trace the margins of the individual bones included in the anteroposterior projection: clavicle, humerus, scapula, and the ribs. Start at the upper aspects of each bone and work clockwise round its margin. Once you have assessed the cortex, examine the internal structure of the bones for distortion of the trabecular pattern. Difficult areas due to overlying structures include:

Humeral head–Posterior dislocation is typically associated with an anteromedial fracture of the humeral head, which is identified as a curvilinear density superimposed on the humeral head, parallel to the articulating cortex (trough sign–fig 8).

The glenoid fossa, coracoid process, and body of the scapula because of overlying ribs. An avulsion fracture of the anteroinferior lip of the glenoid fossa is a common complication of dislocation of the shoulder.

Fractures of the inner third of the clavicle are uncommon and may be missed because of superimposition of the ribs.

Check cartilage and joints

The glenohumeral joint should be examined carefully as posterior dislocation of the shoulder joint may look almost normal on this view. When posterior dislocation is suspected subtle radiographic signs should be sought. Always take an axial view to exclude or confirm such a dislocation. The distance from the humeral head to the anterior margin of the glenoid fossa is usually equal from top to bottom. Asymmetry can be due to dislocation or fracture. Anterior dislocation of the humerus is the most common (fig 6). Intra-articular fractures commonly cause haemarthroses or effusions which displace the head of the humerus inferolaterally–so called pseudosubluxation (fig 9).

Acromioclavicular joint–Check the acromioclavicular joint and distance from the tip of the coracoid process to the clavicle. If there is minimal widening of the joint take stress views. When the acromioclavicular joint is completely torn (grade 2) there is usually widening of the joint as well as superior displacement of the clavicle. In grade 3 injury abnormal widening of the acromioclavicular joint and increased distance between the clavicle and coracoid process can be seen on the standard anteroposterior radiography (fig 5).

Check soft tissues

Disruption of the acromioclavicular joint is usually associated with swelling above the joint, which can be seen with the aid of a bright light. In patients who have not experienced trauma the soft tissues should be examined for calcification, although this may overlie the bones (fig 10). Look for lipohaemarthroses or effusions around the joint capsule (fig 9).

This is a notoriously difficult radiograph to interpret because of its unusual projection and overlying structures (fig 3). Nevertheless, by following an ordered system the anatomy and any abnormality can be detected.

Check the adequacy and quality of the radiograph

The coracoid process, glenoid fossa, acromion process, spine of the scapula, and less tuberosity of the humeral head should be identifiable.

Check alignment of bones

Identify the coracoid process anteriorly and the acromion process posteriorly. The glenoid fossa is projected between these structures. The humeral head should sit within the fossa (fig 3b).

Check bone margins and density

Trace the margins of the clavicle, humerus, and scapula (spine, acromion, glenoid fossa, and coracoid process) clockwise. Fractures of the coracoid process and infraspinous processes of the scapular body are clearly seen in the axial view.

Check cartilage and joints

Examine the acromioclavicular and glenohumeral joints for separation or dislocation.

Check soft tissues

Calcification of the rotator cuff can be seen more clearly in axial views.

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