Upper Extremities
Clavicle
Anatomy & Pathology
Anatomy Overview
The clavicle is a long, slender bone forming the anterior portion of the shoulder girdle. It acts as a strut between the sternum and scapula, helping stabilize the shoulder.
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Key Structures: sternal extremity (medial end), acromial extremity (lateral end), shaft (body), acromioclavicular joint (AC), sternoclavicular joint (SC), acromion process of the scapula, upper ribs (as landmarks)
Common Pathologies
- Fractures: Most frequent in the midshaft; common in falls and athletic trauma.
- Dislocations: May occur at the AC or SC joints, altering clavicular alignment.
- Osteolytic or metastatic lesions: Destructive or sclerotic changes from metastatic disease.
- Degenerative changes: Arthritic involvement of AC or SC joints, often with joint space narrowing and subchondral sclerosis.
Routine Projections (ARRT Required)
AP Clavicle
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright or supine; supine preferred for trauma
- Adjustments: Arms at sides, shoulders in same horizontal plane
- CR: Perpendicular to midshaft of clavicle
- Pt. Instructions: Suspend at the end of exhalation for uniform density
- Exposure: Moderate kVp and mAs to visualize clavicle and adjacent structures
Evaluation Criteria
- Coverage: Entire clavicle centered and including both AC and SC joints
- Rotation checks: Lateral half of clavicle above scapula; medial half superimposing thorax; SC joints symmetrical
- Motion checks: Sharp cortical margins without blur
- Technique checks: Proper penetration at SC joint without overexposure of lateral end
- Clinical aim: Demonstrates frontal anatomy of the clavicle in true AP projection
AP Axial (Semi-Axial) Clavicle
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright (lordotic preferred) or supine if unable to stand
- Adjustments: Center clavicle to IR; in upright, lean backward in extreme lordosis or angle CR cephalad when supine
- CR: Cephalic angle of 15–30° to midshaft of clavicle (thinner patients require greater angulation)
- Pt. Instructions: Suspend at end of full inspiration to elevate clavicle above ribs
- Exposure: Slightly higher kVp than AP to penetrate thorax
Evaluation Criteria
- Coverage: Entire clavicle from SC to AC joint
- Rotation checks: Clavicle projected above ribs and scapula; medial end overlapping 1st or 2nd rib
- Motion checks: Sharp margins without ghosting
- Technique checks: Uniform brightness and detail throughout length
- Clinical aim: Projects clavicle free of thoracic superimposition; evaluates displacement and alignment
Supplementary Projections
PA Clavicle
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright or prone; PA preferred to reduce OID and improve recorded detail.
- Adjustments: Shoulders in the same transverse plane; arms relaxed at sides.
- CR: Perpendicular to the midshaft of the clavicle.
- Patient instructions: Suspend respiration at end of exhalation for uniform density.
- Exposure: 70–80 kVp; moderate mAs for good penetration through thorax.
Evaluation Criteria
- Coverage: Entire clavicle including both AC and SC joints.
- Rotation checks: SC joints symmetric; medial end superimposed on upper ribs.
- Motion checks: Sharp cortical margins; no motion blur.
- Technique checks: Balanced exposure—lateral end not overexposed.
- Clinical aim: Provides frontal view with improved sharpness and less magnification than AP; useful for slender or pediatric patients.
PA Axial Clavicle
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright or prone.
- Adjustments: Align shoulders on the same horizontal plane; center clavicle to midline of IR.
- CR: 15–30° caudad (angle varies with patient thickness: 15° for broad shoulders, up to 30° for thin body habitus), directed to midshaft of clavicle.
- Patient instructions: Suspend at end of full inspiration to elevate clavicle above ribs.
- Exposure: 75–85 kVp; short exposure time.
Evaluation Criteria
- Coverage: Entire clavicle, including both AC and SC joints.
- Rotation checks: Clavicle projected above ribs and scapula, free of superimposition.
- Motion checks: Distinct cortical margins; no double outlines.
- Technique checks: Even density across length of bone.
- Clinical aim: Demonstrates the clavicle free of thoracic superimposition with reduced magnification; often preferred over AP axial for trauma patients who can lie prone.
Axial Lordotic (Standing Lordosis) Clavicle
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright with back against IR; lean backward in extreme lordosis so shoulders rest against IR.
- Adjustments: Center mid-clavicle to IR; chin raised to clear clavicle.
- CR: Perpendicular to IR (body angulation provides cephalic projection equivalent to 15–30°).
- Patient instructions: Suspend at end of full inspiration to raise clavicle.
- Exposure: 75–85 kVp; short time.
Evaluation Criteria
- Coverage: Entire clavicle including both joints.
- Rotation checks: Lateral half above scapula; medial half superimposed on thorax.
- Motion checks: Sharp cortical detail; no ghosting.
- Technique checks: Consistent brightness along shaft.
- Clinical aim: Alternative to AP axial projection when tube angulation is limited; uses patient lordosis to project clavicle clear of thorax.
Tangential (Serendipity) View – Sternoclavicular End
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine or upright; head turned slightly away from affected side.
- Adjustments: Center at level of T3 (about 2 inches below jugular notch).
- CR: 40° cephalad toward the sternoclavicular joint of interest.
- Patient instructions: Suspend respiration.
- Exposure: 75–85 kVp; short exposure time.
Evaluation Criteria
- Coverage: Medial half of clavicle and sternoclavicular region.
- Rotation checks: Affected SC joint projected above the opposite one; joint space open.
- Motion checks: Sharp margins; no breathing motion.
- Technique checks: Adequate penetration through mediastinum.
- Clinical aim: Evaluates medial clavicular displacement and SC joint injuries—particularly useful for posterior dislocations not well seen on standard AP or axial images.
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Hows & Whys of Clavicle Radiography
Anatomy
- What is a common term for the clavicle?
The collarbone. - With what bone does the medial end of the clavicle articulate?
The manubrium of the sternum at the sternoclavicular joint. - With what bone does the lateral end of the clavicle articulate?
The acromion process of the scapula at the acromioclavicular joint.
Positioning
- Why might a PA projection be preferable to an AP?
The PA projection reduces OID, minimizing magnification and improving spatial resolution. - Why is the patient instructed to suspend at the end of exhalation for the AP view?
End-expiration lowers the shoulders slightly, allowing the clavicle to assume a more horizontal orientation and improving density uniformity. - Why is full inspiration used for the AP axial projection?
Full inspiration elevates the clavicle, projecting it above the ribs for clearer visualization. - Why is a cephalic angulation used in the AP axial projection?
The angle frees the clavicle from thoracic structures, improving visibility of its entire length. - Why might thinner patients require more angulation?
Thinner thoraxes have less natural curvature, requiring greater CR tilt (up to 30°) to clear the ribs.
Technique & Image Evaluation
- How can you tell the image is a true AP?
The SC joints are symmetrical, and the clavicle appears horizontally across the thorax without rotation. - How can you tell the axial projection was angled correctly?
The clavicle appears more horizontal and is projected above the upper ribs without overlapping lung apex. - How can you tell if rotation occurred?
Unequal spacing of the SC joints or distortion of the thoracic spine relative to clavicle alignment. - How can you tell if exposure was adequate?
The medial end near the SC joint should be visible without burnout, and the lateral end should retain trabecular pattern.
Clinical Applications
- When is an axial projection preferred?
To clear the clavicle from thoracic structures, evaluate displacement after trauma, or detect subtle fractures. - Why might a PA axial be used instead of AP axial?
It provides better detail and less distortion since the clavicle lies closer to the image receptor. - What special consideration applies for trauma imaging?
When fracture is suspected, the supine position minimizes movement and reduces risk of further displacement.
