Shoulder & Scapula Text

Shoulder & Scapula

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This discussion of the shoulder will include the glenohumeral (shoulder) and acromioclavicular joints, the proximal humerus, scapula, and clavicle. Acute soft tissue injuries of the shoulder demonstrated best by MRI, such as those of the rotator cuff and glenoid labrum, are not part of emergency center practice and will not be presented.

The radiographic appearance of the proximal humeral physis (fig. sh01) can be the most confusing of all physes in that one margin of the plate-like physis is frequently projected on the metaphysis and may simulate a fracture. This dilemma is resolved either by repeating the frontal projections of the injured shoulder in other degrees of rotation, or by obtaining comparable views of the opposite shoulder. Close inspection of the physeal margin superimposed on the metaphysis should reveal its characteristics to be those of a physis rather than an acute fracture.

RADIOGRAPHIC EXAMINATION & ANATOMY

The standard views of the shoulder include AP internally and externally rotated, AP of the glenohumeral space, and axillary projections. Conventional imaging for acromioclavicular (A/C) joint separation requires only an erect AP projection of each shoulder. Stress views of the A/C joint obtained with 10-pound weights strapped to the wrists should be obtained only when the initial examination is either negative or equivocal in the presence of high clinical suspicion of A/C joint separation.

The internally and externally rotated projections are obtained with the patient erect, forearm flexed, back parallel to the cassette and the x-ray beam centered on the glenohumeral space just medial to the humeral head. The internally rotated projection (fig. sh02), characterized by the round (rifle barrel, light-bulb) appearance of the humeral head, is obtained with the forearm in front of the abdomen. Conversely, external rotation (fig. sh28) at the shoulder with the flexed forearm laterally perpendicular to the lateral chest wall results in the externally rotated AP projection characterized by visualization of the humeral neck between the humeral head and shaft.

The AP view of the glenohumeral space (fig. sh04) is obtained with the patient rotated in the injured shoulder posterior oblique position, the scapula parallel to the cassette, and the x-ray beam centered on the glenohumeral space.

The anatomic structures seen on these three frontal projections are the same, varying only by virtue of the different projection. Structures to be identified include the humeral head, greater and lesser tuberosities, bicipital groove, glenoid fossa, acromion and coracoid processes of the scapula, scapular spine, distal end of clavicle and acromioclavicular joint.

The axillary view (fig. sh05) is important because it is the only orthogonal projection of the shoulder. It does not require 90° abduction of the arm as is illustrated in most texts of radiologic positioning. To abduct the arm to that degree in the presence of a possible fracture or dislocation of the shoulder is contrary to all tenets of acute fracture management. A perfectly diagnostic axillary projection is obtained with only 10-15° of gently assisted abduction. The central beam is directed to the apex of the axilla with the cassette above the shoulder and perpendicular to the central beam.

The radiographic examination and anatomy of the scapula and clavicle will be described and illustrated in each of those subsections.

INJURIES OF THE SHOULDER

PEDIATRIC

Physeal injuries of the shoulder are not common. The most common is the Salter-Harris Type II of the proximal humeral physis (fig. sh29) which is an oblique metaphyseal fracture line that extends into, and disrupts, part of the physis. The proximal fragment consists of the epiphysis and triangular metaphyseal fragment adherent to the epiphysis through the intact physis. The radiographic characteristics of the physis and the fracture line should make the distinction clear.

ADULT

GLENOHUMERAL DISLOCATION
Classification
	Anterior (95%)
		Infracoracoid
		Infraglenoid
		Luxatio erecta
	Posterior (5%)
		Dislocation (rare)
		Fracture dislocation (common)

Infracoracoid Dislocation (figs. sh07, sh08, sh09, sh10) occurs when the humeral head is displaced anteriorly to lie in the infracoracoid space. The humeral head may impact on the anterior labrum of the glenoid resulting in the Hill-Sacks fracture.

The Hill-Sacks fracture (fig. sh11) was originally described as a wedge-shaped defect in the posterolateral aspect of the humeral head (seen best on the internally rotated projection). The Hill-Sacks fracture is simply an impaction fracture of the humeral head that may range in appearance from a wedge deficit to a short arc of cortical flattening. A Hill-Sacks type fracture may occur at any site of the humeral head that impacts on the glenoid rim or the coracoid process.

The Bankhart fracture (figs. sh13, 15, 16, 17) results from impaction of the anterior or anterosuperior (anterior dislocation) or posterior (posterior dislocation) glenoid labrum by the displaced humeral head / is an osteochondral fragment. Although the Bankhart fracture occurs more commonly (by MRI and arthroscopy) than the Hill-Sacks, the Bankhart fragment is less visible radiographically because the fragment is primarily cartilaginous.

The infraglenoid dislocation (fig. sh11) is characterized by the humeral head coming to lie inferior to the glenoid. In this instance, impaction involves the superior arc of the humeral head.

Luxatio erecta (fig. sh12) occurs as the result of a fall in which one, or both, arms are forced into severe (nearly 180°) abduction. The humeral head is levered out of the glenoid fossa into the space between the glenoid and the coracoid process. The humeral head may impact on the coracoid process causing a Hill-Sacks type fracture of its anterosuperior arc. Luxatio erecta is distinguishable from other anterior dislocations by the superior orientation of the humeral shaft. Clinically, the arm is locked in severe abduction so that the arm is essentially parallel to the side of the face and head and the forearm flexed across the top of the head.

Posterior dislocation. Posteriorly displaced injuries of the glenohumeral joint, characterized by the humeral head being posteriorly displaced with respect to the glenoid, represent approximately 5% of glenohumeral separation and include pure dislocation (extremely rare) and fracture-dislocation (common).

Conventional radiographic signs of posterior displacement of the humerus include morbid internal rotation and the “trough” sign (fracture-dislocation) which represents the impacted fracture of the humeral head by the posterior glenoid rim (fig. sh16, 14, 15). The lateral wall of the “trough” represents the depth of the impacted fracture and the medial wall, the more posterior normal subchondral cortex of the humeral head (figs. sh16, 14). Typically, however, the lateral wall of the “trough” is either poorly or non-defined because of the comminution of the humeral head fracture (fig. 18, 19). In this instance, posterior fracture-dislocation is indicated by internal rotation of the humerus and fracture fragments. The axillary view confirms the diagnosis.

Scapula

Scapular fractures are frequently considered to be of little consequence except for pain. They are also commonly radiographically subtle. For these reasons scapular fractures are commonly missed particularly on the initial chest radiograph obtained in the trauma bay of multiply injured patients and even on subsequent portable chest radiographs obtained in the intensive care unit [?]. Scapular fracture may be missed on the initial supine chest radiograph for several reasons:

The lateral aspect of the scapula is not included on the film,
The fracture is obscured by technical artifacts (e.g., radiographic labels or EKG leads)
Subcutaneous emphysema
Pulmonary contusion
Rib and clavicular fractures (fig. sh36)

The latter effects of trauma are commonly used as justification for overlooking scapular fractures. Scapular fractures are more likely to be recognized if the soft tissue and skeletal injuries are used in a positive fashion to raise the index of suspicion regarding the presence of a scapular fracture. Fractures of the scapular neck and glenoid are commonly treated by open reduction and internal fixation. Therefore, it is important to identify neck and glenoid fractures early so they can be treated at the time of other orthopedic surgery rather than requiring a second anesthesia and operation.

RADIOGRAPHIC EXAMINATION & ANATOMY

ADULT

The routine views of the scapula are the AP (fig. sh30) and lateral (axial, tangential, “Y”) (fig. sh31). The axial view provides an orthogonal view of the structures of the lateral-most aspect of the scapula. The skeletal anatomy shown on these projections includes the glenoid fossa, neck, acromion and coracoid processes, spine, and supra- and infraspinous (body) portions.

AP scapula, (fig. sh30) may be obtained with the patient either supine or erect.

Lateral scapula (fig. sh31) is obtained either erect or supine. The patient is rotated into the injured side anterior oblique (approximately 45 degrees) position, with the arm at the side and the central beam centered on the scapula.

Positioning for the axillary view (fig. sh05) has been previously described.

PEDIATRIC

The physis at the base (fig. sh32) and tip (fig. sh34) of the coracoid and the acromion (fig. sh33), should be readily distinguishable from fractures on the basis of the patient’s age and the predictable location and radiographic characteristics of the physis.

SCAPULAR INJURIES

Acromioclavicular (A/C) SeparationThe ligaments involved in A/C separation include the acromioclavicular and the coracoclavicular. The former is relatively thin, while the coracoid, consisting of the coroid and trapezoid ligaments, is thick and tough and is the principal ligamentous attachment of the upper extremity to the torso through the clavicle (fig. sh20). It is of interest that the term “coracoid” does not appear in the name “acromioclavicular separation” yet it is the important ligament.

While A/C separation may occur with major trauma, e.g., scapulothoracic dissociation, it typically is an isolated injury. Therefore, the initial examination should be an erect AP radiograph of the shoulder (fig. sh21). Normally, the inferior cortex of the distal end of the clavicle and of the acromion should be on the same plane or the same continuous arc across the A/C space. This does not apply to the superior cortices where that of the clavicle is typically at a higher level than the superior cortex of the acromion. If the initial radiograph shows a Type III A/C separation, no other imaging is necessary. If the initial radiograph is negative or equivocal and the clinical suspicion persists, frontal examination of each shoulder with weights – as previously described – should be obtained to demonstrate a Type I or II A/C separation. In either injury, the weights on the injured side will cause the A/C space to widen and/or the acromion to be pulled inferior to the distal end of the clavicle.
MOI: Blow to superior surface of the acromion.
Pathology: Type I tear of the acromioclavicular ligament; Type II tear of A/C and attenuation or partial tear of C/C ligaments; Type III complete tear of both A/C and C/C ligaments.
Radiographic Signs
      Type I: Negative or very slight discrepancy between inferior cortex of distal end of clavicle and acromion (fig. sh24). Erect AP radiograph with 10^th weight to wrist accentuates A/C discrepancy (fig. sh25).
      Type II: Abnormally wide A/C and C/C spaces (fig. sh22). Subjectively, the degree of separation at each space is less than with Type III, however the radiographic distinction may be subtle.
      Type III: Grossly abnormal A/C and C/C spaces on erect AP radiograph without added weight (fig. sh23).
Additional Imaging: not necessary
NB: Types IV, V, and VI A/C separation have been recently described [ ]. These occur rarely and are illustrated and described in The Radiology of Emergency Medicine, 4th ed.[ ].

SCAPULAR FRACTURES

The early diagnosis of fractures of the glenoid fossa (fig. sh37, sh38) and scapular neck is important since the treatment of each is by open reduction and internal fixation.

The Type I (fig. sh39) coracoid process fracture (base) is usually comminuted, displaced and visible on an AP radiograph of the shoulder. The Type II (fig. sh40) corocoid process fracture (tip) is usually only visible on the axillary projection because of the anterior orientation of the coracoid process to the central x-ray beam on the AP radiograph of the shoulder.

Supraspinous fractures are frequently difficult to recognize on the AP radiograph of the shoulder because of superimposition of the clavicle and upper ribs.

Infraspinous fractures, even though displaced are commonly subtle on the frontal radiograph of the shoulder. These are best seen on "Y" view.

Additional Imaging
The tangential (“Y”, lateral), when possible to obtain, provides excellent delineation of most scapular fractures.

CT: Only when fractures of the glenoid fossa and/or neck are either suspected on the basis of conventional radiographs or to more accurately define the extent of glenoid or neck fractures seen on shoulder radiographs.

Scapulothoracic Dissociation (S-TD). Scapulothoracic dissociation is the result of massive trauma to the shoulder resulting in lateral displacement of the scapula, and consequently the upper extremity, with respect to the thoracic cage. S-TD is associated with major injury to the brachial plexus and axillary artery and/or its branches. Radiographically, S-TD is associated with laterally distracted clavicular fractures, A/C separation, or sternoclavicular dissociation or any combination (fig. sh41, sh42). The scapula itself may be fractured, as may the proximal humerus.

Clinically, S-TD is associated with a large axillary hematoma and brachial plexus paresis.

CLAVICLE

Clavicular injuries include fractures of the distal, middle and proximal thirds and sternoclavicular dissociation. The latter will be discussed in the chest chapter.

Distal Third Clavicular Fractures are commonly associated with disruption of the coracoclavicular ligament while the A/C ligament remains intact maintaining the A/C relationship. In the erect position, the distal clavicular fragment and the upper extremity are inferiorly displaced with respect to the distal end of the proximal clavicular fragment (fig. sh45).

Mid-Third Clavicular Fractures are commonly obscured by superimposed ribs and the scapula. Such fractures, when minimally displaced, are best seen on the tangential view of the clavicle (fig. sh43, sh44).

Proximal Third Clavicular Fractures are typically subtle due to minimal displacement and superimposed skeletal parts. While oblique radiographs of the sternoclavicular joints, made with the patient prone, have been described to demonstrate this anatomy, positioning is frequently difficult and painful and the images only marginally useful. Supine axial CT of the sternoclavicular joints will reveal proximal third clavicular fractures.

PROXIMAL HUMORUS

Fractures of the humoral head and neck are classified according to the system of Neer [?], which is based on the number of fragments, their degreee of displacement, and the location of the principal fracture line with reference to the anatomic (physis) (fig. sh48, sh49) and surgical (junction of shaft and neck) (fig. sh46, sh47) neck of the humerus. The four possible fragments include the humeral head, the shaft, and the greater and lesser tuberosities. Two-part fractures, whether of the anatomic (figs. sh46, sh47) or surgical necks are readily apparent on conventional radiographs of the shoulder. Three and four-part fractures are recognizable radiographically, but are more clearly defined by CT.

Questions regarding emergency radiology should be directed to Dr. Harris. Concerns or questions regarding the function or design of this site should be directed to Thea Troetscher, RN.

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GLENOHUMERAL DISLOCATION