Procedures · Upper Extremity

Shoulder Positioning Series

Compare AP external and AP internal rotation in the routine nontrauma shoulder series.

shoulder · External rotation

Right

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The routine shoulder series

The projections this region is examined with. Set them up yourself in Practice positioning.

AP shoulder — external rotation

Anteroposterior projection · arm externally rotated, hand supinated

Demonstrates: A frontal projection of the proximal humerus with the lateral two-thirds of the clavicle and the upper scapula, including how the humeral head sits against the glenoid cavity. Full external rotation announces itself at the greater tubercle, which is thrown into full profile on the lateral side of the proximal humerus; the lesser tubercle has gone round to the front and projects over the humeral head rather than over either margin.
Part position: Erect or supine — erect is usually the more comfortable of the two if the patient can manage it. Rotate the body slightly toward the affected side as far as it takes to bring the shoulder into contact with the receptor or the tabletop, and set the patient so the scapulohumeral joint sits at the centre of the receptor. Abduct the extended arm slightly, then externally rotate it by supinating the hand until the epicondyles of the distal humerus lie parallel to the receptor and the same distance from it. Suspend respiration for the exposure.
Central ray: 90° to the image receptor, centered 1 inch (2.5 cm) inferior to the coracoid process.
Why it is positioned this way: The arm is a cylinder, so a shoulder image tells you nothing about rotation until you know where the two tubercles have ended up — and that is exactly what the position is set to control. In the anatomic position the greater tubercle sits on the outside of the proximal humerus and the lesser tubercle sits at the front, and supinating the hand rolls the whole bone until the greater tubercle faces straight out to the side. Once it does, the beam meets it edge-on and it appears in profile on the lateral margin, which is the single check for this projection. The lesser tubercle, still facing the tube, has nothing to project against a margin and instead lands over the middle of the head. Notice that the check you make in the room is a different one: you palpate both epicondyles at the far end of the same bone and level them against the receptor, because the humerus turns in one piece and levelling one end is what squares up the other. If you pronate the hand by mistake, the radius rolls across the ulna, carries the humerus with it, and the greater tubercle slides quietly off the lateral margin — the image becomes an oblique, and there is nothing on it that says so except the tubercles.

Also covered by this projection

Finding the coracoid processThe centring point is 1 inch — 2.5 cm — below the coracoid process, and on most patients the coracoid cannot be felt directly. Approximate it instead: it lies roughly 2 inches, or 5 cm, below the lateral portion of the acromioclavicular joint, which is easy to palpate. Work from the AC joint down and you land close enough.

Receptor and collimationA 10 × 12 inch (24 × 30 cm) receptor placed landscape, with a grid, at a minimum 40 inch (100 cm) source-to-image distance. Turn the receptor portrait instead when the proximal aspect of the humerus is what needs demonstrating. Collimate on all four sides, bringing the lateral and upper borders in to the soft tissue margins of the shoulder.

Do not rotate an arm that may be brokenSupinating the hand turns the whole humerus, which is precisely what a fractured or dislocated proximal humerus must not do. If either is suspected, leave the arm as it lies and use the trauma routine instead: an AP in neutral rotation, then either a transthoracic lateral or a PA oblique scapular Y lateral. Those are a separate routine box, not additions to this one.

AP shoulder — internal rotation

Anteroposterior projection · arm internally rotated until the epicondyles stand at 90° to the receptor

Demonstrates: The same field — proximal humerus, lateral two-thirds of the clavicle, upper scapula and the humeral head against the glenoid cavity — but now a lateral view of the proximal humerus itself. Full internal rotation announces itself at the lesser tubercle, which has come round into full profile on the medial side of the humeral head; the greater tubercle has swung to the front and shows only as an outline over the head, so the lateral margin reads as a smooth dome.
Part position: Erect or supine, exactly as for the external rotation: body turned slightly toward the affected side until the shoulder rests against the receptor, and the scapulohumeral joint centred to the receptor. Abduct the extended arm slightly, then internally rotate it by pronating the hand until the epicondyles of the distal humerus stand at 90° to the receptor. Suspend respiration for the exposure.
Central ray: 90° to the image receptor, centered 1 inch (2.5 cm) inferior to the coracoid process.
Why it is positioned this way: Compare this tab with the last one and notice what has not changed: the tube, the receptor, the centring point, and the scapula behind the arm. Everything different about this image comes from the humerus having turned a quarter of a circle inward inside a shoulder that stayed still — which is why you can set both projections up without moving a single piece of equipment between them. Follow what that quarter-turn does to the two tubercles. The greater tubercle starts on the lateral margin and swings forward to face the tube, where it projects over the middle of the head as a faint outline and leaves the outer border of the humerus as a plain rounded curve. The lesser tubercle, which was facing the tube, swings inward to the medial side and takes its turn in profile, where the lower part of the glenoid cavity partly covers it. So the tubercles are the fastest way to read which of these two images you are holding: greater tubercle notching the outer margin means external rotation, lesser tubercle notching the inner margin means internal rotation. And note what this projection is called — it is still an AP projection of the SHOULDER, because the beam still enters the front of the patient and leaves the back. It is the proximal HUMERUS inside it that has become a lateral.

Also covered by this projection

Neutral rotation is the third position, and it belongs to traumaBetween these two lies a third arm position. Let the palm face inward toward the thigh and the epicondyles come to roughly 45° to the receptor, which puts the humerus in an oblique about midway between the two: the greater tubercle sits anteriorly but is still lateral to the lesser. That is neutral rotation, and it is the AP of the trauma routine — the position you use when turning the arm is not an option at all.

The special projections, and what each one is forBeyond these two the chapter files several projections as special rather than routine, each aimed at something these two cannot show. The inferosuperior axial (Lawrence method, and the Clements modification of it) and the PA transaxillary (modified Bernageau) look through the joint from below or from the front to open the scapulohumeral joint itself. The AP oblique (Grashey method) rotates the patient to put the glenoid cavity in profile so the joint space opens fully. The apical AP axial angles the beam to look under the acromion. The tangential projection (Fisk modification) skims the intertubercular sulcus — the groove between the two tubercles — end-on. None of them is part of the routine, and none replaces it.

This projection is also off the table for traumaPronating the hand turns the humerus just as supinating it does, so a suspected fracture or dislocation rules this projection out along with the last one. The trauma routine covers the same ground without asking the injured bone to move: an AP in neutral rotation, then a transthoracic lateral shot through the opposite side of the chest, or a PA oblique scapular Y lateral taken with the patient obliqued toward the receptor.

Procedures lessonShoulder girdle