AC Joints AP is a radiography positioning projection of the Upper Extremity. Erect, bilateral AC joints. Arms at sides, no weights. SID 72" to fit both joints on one image (Bontrager: 40" minimum, or 72"; Merrill's: 72"). The centering point is located midline at the level of the AC joints, about 1 inch above the jugular notch, with both shoulders level and equal exposure intended. The central ray is perpendicular to the midline at the level of the AC joints. Image-quality criteria include both AC joints visualized on one image for side-by-side comparison, AC joints and soft tissues clearly demonstrated. The SID is 72 inches (183 cm).
Anatomy demonstrated
- Bilateral acromioclavicular joints.
- Distal third of both clavicles.
- Medial clavicles and sternoclavicular joints.
Patient preparation
- Verify patient identity using two identifiers.
- Remove necklaces and other radiopaque objects from the region to be radiographed.
- Position patient erect with the back against the IR.
- Let the arms hang unsupported at the sides.
- Keep shoulders level and relaxed throughout the exposure.
Position & centering point
Midline at the level of the AC joints, about 1 inch above the jugular notch, with both shoulders level and equal exposure intended.
Central ray
Perpendicular to the midline at the level of the AC joints.
Exposure / technique
- kVp
- N/A
- mAs
- N/A
- SID
- 72" (183 cm)
- Notes
- Upright bilateral technique without weights; the weighted comparison is a separate projection. Bontrager: minimum SID 40" (102 cm), or 72" (183 cm) to include both joints on the same study or for a broad-shouldered adult. Merrill's text: 72", to reduce magnification and joint-space distortion. Bontrager digital range: 75 to 85 kV. Merrill's chart prints 81 kVp, DR 5.6 / CR 11 mAs for a 14 cm part, but at a 40" SID, so adjust for 72" and your equipment. Bontrager: complete shoulder or clavicle projections first to rule out fracture, or take and check this view before the weighted one.
Image-quality criteria
- Both AC joints visualized on one image for side-by-side comparison.
- AC joints and soft tissues clearly demonstrated.
- Entire clavicles and SC joints included.
- Both AC joints on the same horizontal plane.
- No rotation: SC joints symmetric on each side of the vertebral column.
- Collimation: long, narrow field with the upper border at the upper shoulder soft tissue margin (Bontrager); 6 x 17 inches (15 x 43 cm) for both joints on one exposure (Merrill's).
Common errors
- 1 Shoulders not level: both AC joints should lie on the same horizontal plane.
- 2 Patient rotated: the SC joints look asymmetric.
- 3 CR not midway between the AC joints, 1 inch above the jugular notch.
- 4 Field not collimated long and narrow to the area of interest.
Clinical indications
- Acromioclavicular joint separation or dislocation.