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Procedures · Upper Extremity
Scapula Positioning Series
Compare the AP and lateral projections of the routine scapula series.
AP
Right
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AP scapula
Anteroposterior projection · arm abducted 90°, hand supinated
- Demonstrates
- A frontal projection of the whole scapula — both angles, the vertebral and lateral borders, the acromion, the coracoid process and the glenoid cavity, together with the lateral portion of the clavicle and the proximal humerus. The lateral portion of the scapula stands clear of the ribs and the humerus; the medial portion is read through the thoracic structures behind it, so it appears fainter without disappearing.
- Part position
- Erect or supine, with the posterior surface of the affected shoulder in contact with the image receptor and the thorax square to it — no rotation toward either side. Gently abduct the arm to 90° and supinate the hand. Center the receptor to the midscapula.
- Central ray
- 90° to the image receptor, centered to the midscapula — about 2 inches (5 cm) inferior to the coracoid process, at the level of the axilla, and about 2 inches (5 cm) medial from the lateral border of the patient.
- Why it is positioned this way
- The scapula spends most of its life hidden. It lies flat against the posterior chest wall with ribs in front of it and behind it, and with the arm at the side the head and shaft of the humerus lie across its lateral part as well. Abducting the arm is what solves the second half of that problem: raising it to 90° swings the humerus up and out to the side, off the lateral border and the neck of the scapula, and it draws the scapula itself a little laterally away from the ribs. Supinating the hand comes along with the abduction and keeps the arm from rolling as it rises. What you cannot do anything about is the ribs, and the projection does not try — the evaluation criteria ask only that the lateral portion be free of superimposition and accept that the medial portion is seen through the thoracic structures. That is why this projection is exposed the way it is: a long exposure taken while the patient breathes quietly blurs the rib and lung detail into an even background, so the medial part of the scapula reads through it instead of competing with sharp rib edges.
Also covered by this projection
The breathing technique, and why automatic exposure control is not usedThis is one of the few routine projections taken with the patient breathing rather than holding still. The technique is called a breathing, or orthostatic, technique: the patient breathes gently and evenly through an exposure of at least 3 seconds, with 4 to 5 seconds more desirable still. The moving ribs and lung markings blur out across that time while the scapula, which barely moves, stays sharp. It has to be set up with manual exposure factors — a low milliamperage paired with a long time to reach the exposure needed. Automatic exposure control is specifically not recommended here, because it terminates the exposure on the radiation reaching its detectors and would end it long before the several seconds this effect needs.
Receptor and collimationA 10 × 12 inch (24 × 30 cm) receptor placed portrait, with a grid, at a minimum 40 inch (100 cm) source-to-image distance. Collimate on all four sides to the borders of the scapula.
Finding the centring point on the patientThree landmarks converge on the same spot, and any of them will get you there. The coracoid process sits about 2 inches (5 cm) above it. The axilla, palpated from the side, is at its level. And it lies about 2 inches (5 cm) in from the lateral border of the patient. Use whichever is easiest to feel on the patient in front of you and cross-check with a second.