Thorax and Abdomen
Sternoclavicular (SC) Joints
Anatomy
Students should be able to identify the following structures on radiographic images:
sternoclavicular joint, clavicular notch, acromioclavicular joint, acromial extremity, sternal extremity, acromion, coracoid process, scapula.
Routine Projections (ARRT Required)
PA Sternoclavicular (SC) Joints
CR Location & Positioning
- SID: 40 inches
- Patient position: Prone or erect
- Adjustments: Arms relaxed at sides, palms posterior to bring shoulders forward and reduce OID; MSP centered to IR midline
- CR: Perpendicular to IR at level of T2–T3 (≈ 3 inches inferior to C7 or at top of scapulae)
- Pt. Instructions: Suspend respiration on expiration (reduces lung volume, equalizes density)
- Exposure: On expiration
Evaluation Criteria
- Coverage: Medial third of both clavicles and manubrium included
- Rotation checks: Medial ends of clavicles equidistant from vertebral column
- Motion checks: Sharp joint margins and manubrial borders
- Technique checks: Balanced exposure for bone and mediastinal soft tissue; no overpenetration
- Clinical aim: Baseline image to compare both joints symmetrically and assess displacement
Anterior Oblique Sternoclavicular (RAO or LAO)
CR Location & Positioning
- SID: 40 inches
- Patient position: Prone or erect
- Adjustments: Rotate patient 10–15° toward side of interest (RAO for right SC, LAO for left); arms relaxed, palms posterior
- CR: Perpendicular to IR at level of T2–T3, centered 1–2 inches lateral toward elevated side (joint of interest)
- Pt. Instructions: Suspend respiration on expiration
- Exposure: On expiration
Evaluation Criteria
- Coverage: Medial third of both clavicles, manubrium, and SC joints
- Rotation checks: Down-side joint free from vertebral superimposition; up-side joint foreshortened
- Motion checks: Sharp joint margins, no blur
- Technique checks: Uniform exposure through thoracic structures
- Clinical aim: Demonstrate the down-side SC joint unobscured by spine for detection of dislocation or asymmetry
Supplemental Projections
Posterior Oblique SC Joints (RPO / LPO)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine or erect (used when anterior obliques not tolerated)
- Adjustments: Rotate 10–15° away from side of interest (RPO for left SC, LPO for right); MSP centered to IR
- CR: Perpendicular to IR at T2–T3, 1–2″ lateral toward elevated side
- Pt. Instructions: Suspend respiration on expiration
- Exposure: On expiration
Evaluation Criteria
- Coverage: SC joints and medial clavicular ends visualized
- Rotation checks: Up-side joint (farthest from IR) clearly visible, down-side foreshortened
- Motion checks: No motion blur
- Technique checks: Slight magnification expected due to increased OID
- Clinical aim: Alternate view when anterior obliques are contraindicated (e.g., trauma, immobility)
Hows & Whys of SC Joint Radiography
Anatomy
- How are the sternoclavicular joints formed?
Each SC joint is formed by articulation between the sternal end of the clavicle, the manubrium of the sternum, and the first costal cartilage. - How does the SC joint type influence its motion?
As a synovial saddle joint, it allows limited gliding and rotation for shoulder mobility while maintaining joint stability. - How can vertebral levels aid in positioning?
The SC joints lie at T2–T3, roughly 3 inches below the vertebra prominens.
Positioning
- Why is the PA projection performed first?
To assess both joints symmetrically and detect overall displacement before isolating either side. - Why are anterior obliques preferred over posterior obliques?
They place the joint of interest closest to the IR, reducing magnification and improving spatial resolution. - Why use 10–15° rotation for obliques?
This degree projects the joint away from the spine without excessive distortion or foreshortening. - Why is expiration used for all SC joint exposures?
Expiration lowers thoracic volume, improving mediastinal contrast and uniform density across both joints. - Why maintain short exposure time?
To reduce motion blur from breathing and cardiac pulsation.
Technique & Image Evaluation
- How can you verify no rotation on the PA view?
Medial clavicular ends appear equidistant from the spine, and both joints are symmetric. - How can you check correct obliquity on an RAO or LAO?
The down-side joint is visible free from vertebral superimposition, and the up-side joint is foreshortened. - How do you confirm proper exposure?
SC joints and manubrium appear with sufficient contrast to visualize joint spaces, without overpenetrating thoracic soft tissue. - How do you identify motion on the image?
Blurring of joint margins or ribs indicates motion — typically due to shallow breathing or heartbeat; repeat with shorter time.
Clinical Applications
- Why perform obliques in addition to a PA?
To isolate each joint and evaluate asymmetry, dislocation, or subluxation that may be obscured in a symmetrical PA view. - Why might the “Serendipity view” be ordered?
This specialized 40° cephalad projection differentiates anterior from posterior dislocations of the clavicle. - Why consider CT for posterior dislocations?
Posterior displacement can impinge on the trachea, great vessels, or mediastinum and requires 3-D assessment. - Why use increased kVp for large or muscular patients?
To penetrate the dense thoracic structures and maintain adequate contrast at the SC joint level.
