14.4 Shoulder Girdle

The Shoulder Girdle Anatomy

The shoulder girdle joins the upper limb to the axial skeleton through the clavicle and scapula. Key landmarks are the humeral greater and lesser tubercles, the glenoid cavity of the scapula, the acromion and coracoid processes, and the acromioclavicular (AC) and sternoclavicular (SC) joints. The intertubercular (bicipital) groove lies between the two tubercles. Because the humeral head and glenoid overlap, projection selection depends on rotating either the humerus or the whole body.

AP Shoulder: Internal vs. External Rotation

For a non-trauma shoulder, two AP projections are taken based on humeral rotation, judged by the epicondyles:

External rotation (palm up, epicondyles parallel) is a true AP of the proximal humerus and profiles the greater tubercle laterally. Internal rotation (palm in/pronated, epicondyles perpendicular) profiles the lesser tubercle and produces the characteristic lightbulb appearance of a lateral humerus. For suspected fracture or dislocation, do not rotate the arm - take a neutral AP and a trans-scapular or axial view instead.

Grashey Method (Open Glenohumeral Joint)

The Grashey method is an AP oblique projection made by rotating the body 35 to 45 degrees toward the affected side until the scapula is parallel to the IR. This opens the glenohumeral joint space and profiles the glenoid cavity, allowing evaluation of joint narrowing or posterior dislocation that a straight AP hides.

Demonstrating Dislocations

The scapular-Y (PA oblique) projection places the patient in a 45-60 degree anterior oblique so the scapular body, spine, and coracoid form a Y. In a normal shoulder the humeral head overlies the junction of the Y. In an anterior dislocation the head lies inferior to the coracoid process (subcoracoid); in a posterior dislocation it lies beneath the acromion (subacromial). The inferosuperior axial (Lawrence method) abducts the arm 90 degrees with a horizontal CR through the axilla to show the joint and dislocations; the transthoracic lateral is used when the arm cannot be moved at all.

Clavicle

The clavicle is imaged AP and AP axial. On the straight AP the clavicle superimposes the ribs and upper scapula. The AP axial clavicle angles the CR 15-30 degrees cephalad (more angle for asthenic or supine patients) so the clavicle is projected above the ribs and scapula, clearing the mid-shaft for fracture detection. A PA axial may be used with a caudad angle.

Scapula

The AP scapula abducts the arm 90 degrees to draw the scapula laterally off the ribs; a breathing technique (slow shallow respiration during a long exposure) blurs overlying lung markings. The lateral scapula uses an anterior oblique (a scapular-Y type position) with the arm placed to demonstrate either the body (arm across the chest) or the acromion and coracoid (arm up).

AC Joints

Acromioclavicular (AC) joint imaging evaluates separation and uses a distinctive protocol: bilateral AP projections taken erect at a 72-inch (183 cm) SID, first without weights and then with 8-10 pound (or up to 15 lb) weights strapped (not held) to each wrist. Comparing the two sets reveals widening of the injured joint under stress. Both joints are included for side-to-side comparison; the CR is directed to the midline at the level of the AC joints (about 1 inch above the jugular notch). A common trap is having the patient hold the weights, which causes muscle contraction that can mask the separation - the weights must be suspended from the wrists.

SC Joints and Bicipital Groove

Sternoclavicular (SC) joints are shown with a PA (least magnification, both joints on one image) or a shallow PA oblique of 10-15 degrees that rotates the vertebrae away and throws the joint closest to the IR clear of the spine. The intertubercular (bicipital) groove is demonstrated tangentially with the Fisk method, the patient leaning forward over the vertically positioned IR with the CR directed to the groove. Keep the marker in the field, use 72-inch SID for AC joints, and never rotate a suspected shoulder fracture.

Evaluation Criteria and a Worked Scenario

A diagnostic AP shoulder shows the appropriate tubercle in profile, the humeral head and glenoid in an anatomic relationship, and soft-tissue detail over the joint. A correct Grashey image shows the glenohumeral joint space open with no overlap of the anterior and posterior glenoid rims. A correct scapular-Y superimposes the humeral shaft over the scapular body with the acromion and coracoid seen as the arms of the Y.

Scenario: A patient arrives after a seizure with the shoulder held in internal rotation and clinical suspicion of a posterior dislocation - a pattern classically missed on a single AP because the head can look deceptively normal. The correct workup is a neutral AP plus a scapular-Y and, if tolerated, a Grashey projection; on the Y view the humeral head projecting beneath the acromion confirms the posterior dislocation. The technologist does not attempt internal or external rotation views on an unstable, possibly fractured shoulder. This decision - protecting the patient while still capturing two projections 90 degrees apart - illustrates the clinical judgment the Procedures category rewards. A final reminder: for the AC joint stress series, image the patient erect (never supine, since gravity is what stresses the joint) and compare the weighted and unweighted films side by side to measure any increase in the coracoclavicular distance.