Upper Extremities
Scapula
Anatomy & Pathology
Anatomy Overview
The scapula is a flat, triangular bone forming the posterior part of the shoulder girdle. It articulates with the clavicle at the acromioclavicular joint and with the humerus at the glenoid cavity.
- Key Structures: coracoid process, acromion, glenoid cavity, scapular notch, lateral angle, superior angle, inferior angle
- Borders: superior, medial (vertebral), and lateral (axillary)
- Surfaces: anterior (costal/subscapular fossa) and posterior (dorsal surface with supraspinous and infraspinous fossae)
- Spine: runs obliquely across the posterior surface, ending in the acromion
- Landmarks: superior angle (level of T2) and inferior angle (level of T7)
Common Pathologies
- Fractures: Usually due to high-impact trauma; most often involve the body or neck of the scapula.
- AC Separation: Displacement of the clavicle relative to the scapula at the acromioclavicular joint.
- Scapular Winging: Protrusion of the medial border from paralysis of the serratus anterior (long thoracic nerve injury).
- Metastatic Lesions: Lytic or sclerotic bone changes from secondary malignancy (often breast or lung).
- Degenerative Change: Arthritic or impingement-related alterations around the acromion or glenoid cavity.
Routine Projections (ARRT Required)
AP Scapula
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright or supine; upright preferred for comfort in trauma or tenderness
- Adjustments: Abduct arm to a right angle (90°) to draw scapula laterally; flex elbow and rest hand comfortably
- CR: Perpendicular to midscapular area, approximately 2 inches inferior to the coracoid process
- Pt. Instructions: Slow, shallow breathing to blur lung detail
- Exposure: Use long exposure time with low mA; utilize breathing technique if possible
Evaluation Criteria
- Coverage: Lateral portion of scapula free of superimposition from ribs; include acromion and inferior angle
- Rotation checks: Scapula horizontal and not slanted
- Motion checks: Shallow breathing should blur lung markings but maintain sharp scapular margins
- Technique checks: Adequate contrast to show trabecular detail through lung field
- Clinical aim: Demonstrates entire scapula, particularly lateral border and inferior angle, free of rib overlap
Lateral Scapula (RAO or LAO)
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright, facing Bucky in anterior oblique position (RAO or LAO)
- Adjustments: Rotate body 45–60° to place scapular body perpendicular to IR; position arm depending on area of interest:
- Acromion/Coracoid: Place back of hand on posterior thorax
- Body: Bring arm across chest to grasp opposite shoulder
- CR: Perpendicular to mid-medial border of scapula
- Pt. Instructions: Suspend respiration
- Exposure: Moderate kVp; ensure sufficient mAs for lateral thickness
Evaluation Criteria
- Coverage: Entire scapula, acromion, and inferior angle included
- Rotation checks: Lateral and medial borders superimposed; scapular body free of rib superimposition
- Motion checks: Sharp trabecular pattern of scapular body
- Technique checks: Sufficient brightness to visualize scapular body through thoracic structures
- Clinical aim: Demonstrates scapular body, acromion, and coracoid in profile; useful in evaluating fractures and dislocations
Supplemental Projections
AP Oblique Scapula
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine or upright AP; posterior oblique with affected side elevated 30°–45° (LPO for left, RPO for right)
- Adjustments: Rotate trunk until the scapular body is oblique to the IR; abduct arm slightly to clear lateral border from ribs without deforming fracture alignment
- CR: Perpendicular to IR, centered to the mid-scapular body (about 2 inches inferior to the coracoid and 2 inches medial to the lateral border)
- Patient instructions: Suspend respiration
- Exposure: Moderate kVp (75–85 digital) with grid; short exposure time
Evaluation Criteria
- Coverage: Entire scapula, including acromion, coracoid, lateral border, and inferior angle
- Rotation checks: Lateral border of scapula separated from ribs; medial and lateral borders not superimposed as in lateral view (intended obliquity)
- Motion checks: Sharp cortical and trabecular detail along borders and spine
- Technique checks: Penetration sufficient to visualize scapular margins through thorax without clipping
- Clinical aim: Oblique projection that reduces rib superimposition over the scapular body when AP or lateral views are limited (e.g., tenderness, early fracture callus)
AP Axial Coracoid Process
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine or upright AP; shoulder in neutral rotation
- Adjustments: Center coracoid to IR (≈ 2 inches inferior and medial to the clavicular concavity); keep MSP aligned without rotation
- CR: 30° cephalad to the IR (range 15°–45° per habitus), directed to the coracoid process
- Patient instructions: Suspend respiration
- Exposure: 70–80 kVp with grid; short exposure time
Evaluation Criteria
- Coverage: Coracoid process elongated and free of self-superimposition; adjacent acromion and glenoid included
- Rotation checks: Clavicular heads symmetric about the spine (no AP rotation)
- Motion checks: Crisp coracoid edges; no breathing blur
- Technique checks: Adequate penetration to show coracoid contour without burnout of superior scapula
- Clinical aim: Profiles the coracoid for suspected fracture, os acromiale/coracoacromial arch variants, or painful coracoid impingement
Tangential Scapular Spine (Laquerrière-Pierquin Method)
CR Location & Positioning
- SID: 40 inches
- Patient position: Upright PA preferred; affected shoulder against IR
- Adjustments: Palpate the scapular spine; angle patient or tube so the CR skims tangentially along the plane of the spine; commonly the patient remains PA and the tube is angled ~45° caudad toward the scapular spine (adjust to individual anatomy)
- CR: Tangential to the scapular spine, entering superior to the spine and exiting inferior to it (center over mid-spine region)
- Patient instructions: Suspend respiration
- Exposure: 75–85 kVp with grid; short exposure time
Evaluation Criteria
- Coverage: Entire scapular spine in profile from the medial end to the acromial end, including adjacent supraspinous and infraspinous fossae
- Rotation checks: Tangential line of the spine appears as a single sharp cortex; adjacent ribs do not obscure the spine
- Motion checks: Fine trabecular pattern along the spine margins; no motion blur
- Technique checks: Sufficient contrast to separate the spine from underlying thorax without excessive noise
- Clinical aim: Isolates the scapular spine for occult or stress fracture evaluation, postoperative assessment, or clarification when standard AP/lateral are inconclusive.
Hows & Whys of Scapula Radiography
Anatomy
- What vertebral levels correspond to the upper and lower margins of the scapula?
Upper margin is at T2; lower margin is at T7. - What is the medical term for the armpit region, and why is it relevant in scapular imaging?
The axilla; it marks the lateral border of the scapula and serves as a landmark for angulation and centering in axial and lateral shoulder projections. - What is the function of the supraspinous and infraspinous fossae?
They serve as attachment sites for the supraspinatus and infraspinatus muscles, respectively, which are part of the rotator cuff.
Positioning
- Why is the arm abducted 90° from the body for the AP scapula?
Abduction moves the scapula laterally, pulling it away from thoracic structures to reduce rib superimposition. - Why is shallow breathing used during the AP scapula exposure?
Slow, continuous breathing blurs lung markings and enhances contrast of bony detail without motion blurring the scapula. - Why is the body rotated 45–60° for the lateral scapula?
This degree of rotation aligns the scapular body perpendicular to the IR, ensuring lateral borders are superimposed. - Why are two arm positions used in the lateral projection?
Each highlights a different region: -
Arm behind the back = acromion and coracoid process
-
Arm across the chest = body of scapula
- Why should the patient face the Bucky for the lateral rather than using a posterior oblique?
The anterior oblique (RAO/LAO) reduces OID and distortion, improving sharpness of the scapular body.
Technique & Image Evaluation
- How can you tell if the scapula was properly abducted on the AP image?
The lateral border is clear of rib overlap, indicating full lateral displacement. - How can you tell if the scapular body was perpendicular on a lateral projection?
The lateral and medial borders are superimposed, producing a crisp vertical edge to the scapula. - How can you tell if the body was under-rotated?
The scapular body overlaps the ribs, showing that the medial border is not yet superimposed. - How can you tell if the humerus obscured the scapula?
If the humeral shaft crosses the scapular body, the arm position was incorrect for the area of interest. - How can you tell if exposure factors were adequate?
You should see fine trabecular pattern and soft tissue outlines through the lung field without over-penetration.
Clinical Applications
- Why is the lateral scapula valuable in trauma cases?
It provides a true lateral view of the scapular body, acromion, and coracoid process, which helps identify fractures, dislocations, or scapular winging. - When is the AP Oblique scapula used?
To project the scapula free of rib superimposition when a standard AP view is inadequate or when oblique trauma views are required. - Why might the coracoid process be imaged separately?
The coracoid can mimic fracture fragments on standard shoulder views; an axial projection isolates its contour. - How can the tangential scapular spine projection assist diagnosis?
It shows spine morphology and attachment zones without rib interference, aiding evaluation of acromial impingement or healed fractures.
