Radiography
Radiologic study of the dislocated or subluxated shoulder should include a minimum of three views: anteroposterior (AP) or true AP (Grashey) view, scapulolateral view (scapular Y), and axillary lateral view. This combination of views provides the best evaluation of the bony structures. Although frequently only soft-tissue injury is present, bony pathology is present in 55% of traumatic dislocations, and plain radiographs are a simple and low-cost screening tool for detecting significant glenoid and humeral bony defects.
True anteroposterior (AP)—Grashey view
This view is obtained by placing the posterior surface of the scapula flat onto the radiography film. This results in a view that is 45° oblique to traditional shoulder AP radiography.
A successful exposure demonstrates the glenohumeral joint space, superoinferior head subluxation, joint congruity, joint degeneration, and other articular abnormalities. Disadvantages to this view exist, including anterior and posterior glenoid overlap, which can obscure Bankart lesions; this overlap may be exacerbated by inadequate radiographic technique. Increased soft-tissue overlap as compared with a traditional AP view lessens the quality of bony detail. Jankauskas et al found this view to be 100% specific but not sensitive (54-65%) for glenoid bone defects. [39]
Scapular Y view
The scapular Y view is obtained by aiming the x-ray beam longitudinally down the axis of the scapular spine (see the image below) to obtain a true lateral view of the glenohumeral joint. The humeral head lies directly over the glenoid fossa; if the shoulder has been dislocated anteriorly, the humeral head will be seen anterior to the glenoid fossa. The Y shape is formed by the projection of the acromion, the scapular body, and the coracoid from the longitudinal axis.
Scapular Y-view of normal shoulder. Courtesy of Wikimedia Commons (Mikael Häggström) [https://commons.wikimedia.org/wiki/File:Y-projection_X-ray_of_a_normal_shoulder.jpg].
Y-view radiograph of right shoulder shows anterior dislocation of humeral head relative to glenoid fossa.
This view may be adequate for evaluating dislocations, but it should never replace the axillary view, which is the most sensitive for detecting subluxations. Like the true AP view, it is a poor choice for evaluating glenoid rim fractures.
Axillary view
The axillary lateral view has many variations. As described originally by Lawrence in 1915, it was obtained with the patient supine, the arm abducted to 70-90°, and the x-ray beam aimed from inferior to superior with 15-30° of medial angulation, depending on the amount of abduction. The resulting radiograph allows detection of AP subluxation/dislocation and anterior or posterior glenoid rim fractures.
One alternative is the modified axillary lateral (or Velpeau) view, which may be a good choice if abduction is poorly tolerated because of pain. In this modification, the arm can be maintained in adduction within a sling, and either the patient leans back 20-30º or a wedge with similar angulation is placed behind the patient’s back.
Another variation is the West Point view, which is most helpful in identifying large glenoid defects and humeral head subluxation. [40] It places the patient prone with the arm abducted to 90° and hanging over the edge of the table. The x-ray beam is directed 25° medially and anteriorly. This position improves visualization of the anteroinferior glenoid rim. West Point axillary views are the most sensitive for finding osseous glenoid fractures. [41]
Stryker-Notch view
The Stryker-Notch view was developed to allow visualization of Hill-Sachs lesions of the posterolateral humeral head. It is obtained with the patient supine. The hand is placed on top of the head with the elbow flexed. The x-ray beam is directed from anterior to posterior with a 10° cephalic angulation. It provides good detail of the posterolateral margin of the humeral head.
Humeral internal and external rotation views
Internal and external rotation views provide oblique visualization of the shoulder joint, with the humeral head overlapping the glenoid rim.
The advantage of these views is that they obtain excellent osseous detail of the greater tuberosity, scapula, clavicle, upper ribs, and soft tissues. The high-quality bony detail is the result of the low density of the surrounding soft tissue. Internal rotation of the arm in the AP view projects the lesser tuberosity medially and the posterolateral aspect laterally, providing a good view of Hill-Sachs lesions. These views are of little value in detecting anterior or posterior dislocation/subluxation.
Computed Tomography and Magnetic Resonance Imaging
For most authors, magnetic resonance imaging (MRI) is the imaging modality of choice for soft-tissue injury. [42] It has been shown to be 91% sensitive in detecting capsulolabral lesions in the early postdislocation period. Specifically, it provides comprehensive visualization of important soft-tissue structures that may be injured in anterior instability, including the anterior labrum, the anterior capsule, and the anterior inferior glenohumeral ligament.
Martins e Souza et al evaluated the accuracy of conventional MRI in determining the severity of glenoid bone loss in 36 patients with anterior shoulder dislocation by comparing results obtained by using conventional MRI with results from arthroscopic measurements. [43] They found that interreader and intrareader correlations of MRI-derived measurements of glenoid bone loss were excellent and that the first and second observers' measurements showed strong and moderate interreader correlation, respectively, with arthroscopic measurements.
Magnetic resonance arthrography uses intra-articular contrast to distend the joint space, allowing space to visualize details of damage to the glenohumeral ligaments and labrum. There is continued debate over whether this additional imaging modality is necessary if an optimized MRI has been obtained.
Computed tomography (CT) is of increasing importance in the assessment of bone defects; it is currently considered the gold standard diagnostic tool for identifying bony defects and quantifying bone loss after recurrent anterior instability. [44] In a study of 70 patients with traumatic anterior glenohumeral instability, Delage Royle et al found that regular radiographs had suboptimal sensitivity, specificity, and reliability for evaluation of glenoid and humeral bone loss. [45] They recommended that CT be considered in the treatment algorithm for accurate quantification of bone loss.
An important use of these advanced imaging modalities is determination of the extent of glenoid bone loss, which is essential for clinical decision-making. There are many measuring methods that use MRI or CT; they can be broadly categorized into two groups: (1) width techniques and (2) best-fit circle techniques. [46]
Width methods include the following:
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Glenoid rim distance
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Glenoid index
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Width-length ratio
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West Point measurement
Best-fit circle techniques include the following [8] :
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Pico method
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Sugaya method
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Dumont arc angle method
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MRI methods
No measurement method has yet been established in the literature as a gold standard; accordingly, the choice of method should be based on available quality imaging and provider preference. Measurements of humeral bone loss, or Hill-Sachs defects, have been less extensively studied but include the use of plain radiographs, MRI, and CT.
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Y-view radiograph of right shoulder shows anterior dislocation of humeral head relative to glenoid fossa.
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Upper: type I superior labrum anterior posterior lesion. Lower: type II superior labrum anterior posterior lesion.
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Upper: type III superior labrum anterior posterior lesion. Lower: type IV superior labrum anterior posterior lesion.
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Scapular Y-view of normal shoulder. Courtesy of Wikimedia Commons (Mikael Häggström) [https://commons.wikimedia.org/wiki/File:Y-projection_X-ray_of_a_normal_shoulder.jpg].
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Axillary view of shoulder with anterior instability.
