Imaging the Shoulder - Systematic Approach
From Standard Radiographs to Advanced MRI Assessment
Imaging Modality Selection for Shoulder Pathology
Radiography: First-line for ALL shoulder presentations. Trauma: AP + axillary lateral minimum
Ultrasound: Dynamic cuff assessment, calcific tendinitis, guided injection. Operator-dependent
MRI: Gold standard for rotator cuff tears, labral assessment, bone marrow oedema, impingement
MR Arthrography: Gold standard for labral tears, partial cuff tears, capsular pathology
CT: Fracture characterisation, glenoid bone loss, three-dimensional planning. Essential for complex fractures
CT Arthrography: MRI alternative for labral assessment, glenoid bone loss quantification
Key: Start with radiographs, then choose advanced imaging based on the clinical question
Critical Must-Knows
- Minimum shoulder trauma series: AP in internal rotation + true axillary lateral. The axillary lateral confirms or excludes dislocation.
- Systematic radiograph reading: ABCS -- Alignment, Bone density, Cartilage spaces, Soft tissues.
- MRI is the gold standard for rotator cuff assessment. Ultrasound is a valid alternative with equivalent sensitivity in experienced hands.
- MR arthrography (direct) is the gold standard for labral pathology -- sensitivity 92% vs 76% for non-contrast MRI.
- CT with three-dimensional reconstruction is essential for glenoid bone loss quantification -- more than 20-25% loss mandates bony procedure (Latarjet).
Examiner's Pearls
- "The Hill-Sachs lesion is best seen on AP internal rotation radiograph. The Bankart lesion (bony) is best seen on Bernageau profile view or CT.
- "Acromion morphology (Bigliani classification): Type I flat, Type II curved, Type III hooked -- Type III associated with impingement.
- "Critical shoulder angle (CSA): more than 35 degrees = higher cuff tear risk; less than 30 degrees = higher OA risk.
- "Rotator cuff tear grading on MRI: high signal on T2 within tendon = tear. Full-thickness: extends from articular to bursal surface.
- "The crescent sign on MRI = high T2 signal at the articular margin of the supraspinatus insertion -- suggests partial articular-surface tear.
Exam Warning
Systematic shoulder imaging is one of the most commonly tested musculoskeletal imaging topics. You must be able to: describe the standard radiographic views and what each shows, read a shoulder radiograph systematically (ABCS), select appropriate advanced imaging (MRI vs MRA vs CT vs USS), and interpret key MRI findings (cuff tears, labral tears, acromion morphology). Classic traps: not requesting an axillary lateral in trauma (missing a dislocation) and relying on non-contrast MRI for labral assessment.
ABCSSystematic Shoulder Radiograph Reading
Memory Hook:ABCS: the systematic approach that ensures you never miss a finding on shoulder radiographs.
ATWAStandard Shoulder Radiographic Views
Memory Hook:ATWA: AP, True AP, West Point, Axillary -- know which view shows what.
CRISTKey MRI Findings in Shoulder Pathology
Memory Hook:CRIST: a systematic MRI checklist ensuring complete shoulder assessment.
Overview
The shoulder is the most commonly imaged upper limb joint in orthopaedic practice, with a broad spectrum of pathology ranging from acute trauma (dislocation, fracture) to chronic conditions (rotator cuff disease, instability, arthritis). A systematic approach to shoulder imaging is essential for both the clinical setting and the fellowship examination, where candidates are frequently asked to describe radiographic views, select appropriate advanced imaging, and interpret MRI findings.
The imaging workup begins with plain radiographs in virtually all presentations. Advanced imaging (MRI, ultrasound, CT, arthrography) is selected based on the specific clinical question. Understanding which modality best answers which question is a key examination skill.
Imaging Algorithm
Acute trauma: Radiographs (AP + axillary lateral minimum). If complex fracture: CT with three-dimensional reconstruction for surgical planning. Rotator cuff symptoms: MRI (non-contrast) or USS. If partial tear suspected on USS: MRI for confirmation. Instability: MR arthrography for labral assessment + CT with three-dimensional reconstruction for bone loss. Calcific tendinitis: AP radiograph + ultrasound. Frozen shoulder: Usually clinical diagnosis. MR arthrography if diagnostic uncertainty. OA assessment: True AP (Grashey) + axillary lateral radiographs.
Critical Imaging Pitfalls
Missing a posterior dislocation: the AP view may look near-normal (lightbulb sign). The axillary lateral is ESSENTIAL to confirm direction of dislocation. Missing a bony Bankart: standard radiographs often miss anterior glenoid rim fractures. CT or West Point view is needed. Overdiagnosing labral tears: sublabral foramen (12-18%) and Buford complex are NORMAL VARIANTS. Underestimating cuff tears on non-contrast MRI: partial articular-surface tears are best detected on MR arthrography.
Clinical Imaging
Imaging Gallery
Systematic Approach
Systematic Shoulder Imaging Assessment
Shoulder Imaging Selection Guide
| Clinical Scenario | First-Line Imaging | Advanced Imaging |
|---|---|---|
| Acute trauma/dislocation | AP + axillary lateral radiographs (MINIMUM 2 views) | CT with three-dimensional reconstruction for complex fractures (proximal humerus, glenoid). MRI for associated soft tissue injury after fracture management |
| Suspected cuff tear | AP radiograph (acromiohumeral distance, calcification) | MRI (gold standard) or USS by experienced operator. MRA if partial tear suspected |
| Recurrent instability | AP + axillary lateral (Hill-Sachs, bony Bankart) | MR arthrography (labral tears, capsular pathology) + CT three-dimensional reconstruction (glenoid bone loss quantification) |
| Acromioclavicular pathology | Zanca view (10-15 degree cephalic tilt AP) | MRI for distal clavicle oedema (osteolysis), ligament assessment. Weighted views for instability (controversial) |
| Calcific tendinitis | AP radiograph (demonstrates calcification) | Ultrasound (confirms location, guides barbotage/aspiration). No MRI needed for isolated calcific tendinitis |
| Suspected OA | True AP (Grashey) + axillary lateral | CT for glenoid wear pattern (Walch classification) pre-arthroplasty planning. MRI for associated cuff status |
Radiographic Assessment
Standard Shoulder Radiographic Views
AP in internal rotation: The arm is internally rotated, positioning the greater tuberosity in profile (overlapping the humeral head). This view shows: Hill-Sachs lesion (posterolateral humeral head compression fracture from anterior dislocation), glenohumeral joint space, and acromial morphology.
AP in external rotation: The arm is externally rotated, positioning the greater tuberosity laterally. This view shows: the greater tuberosity in profile (best for tuberosity fractures), the bicipital groove, and the humeral head articular surface.
True AP (Grashey view): The beam is angled 40 degrees to align with the glenohumeral joint plane. This eliminates overlap between the humeral head and glenoid, providing the most accurate assessment of joint space width and glenoid morphology.
Axillary lateral: ESSENTIAL for trauma. The patient is supine or seated with the arm abducted. The beam passes through the axilla from inferior to superior. This view shows: glenohumeral relationship (confirms or excludes dislocation), anterior and posterior glenoid rim (bony Bankart), Hill-Sachs lesion, and coracoid process.
Y-view (scapular lateral): The beam is tangential to the scapular spine. Shows the relationship of the humeral head to the glenoid fossa -- the head should be centred over the glenoid Y. Anterior dislocation: head is anterior to the Y. Posterior dislocation: head is posterior.
Acromiohumeral distance: Measured on the AP view from the inferior surface of the acromion to the superior surface of the humeral head. Normal: more than 7mm. Less than 7mm suggests massive rotator cuff tear with superior migration of the humeral head.
Evidence Base
MRI vs Ultrasound for Rotator Cuff Tears
- For full-thickness rotator cuff tears: MRI sensitivity 91%, ultrasound sensitivity 92% -- no significant difference.
- For partial-thickness tears: MRI sensitivity 67%, ultrasound sensitivity 67% -- both have limited detection.
- MR arthrography had the highest sensitivity for partial tears at 83%.
Goutallier Classification for Fatty Infiltration
- Fatty infiltration of the rotator cuff muscles was graded 0-4 on CT (later adapted for MRI).
- Grade 3 or higher (more fat than muscle) was associated with significantly poorer outcomes after rotator cuff repair.
- Fatty infiltration was IRREVERSIBLE even after successful cuff repair.
Systematic clinical evidence guides imaging selection for rotator cuff pathology.
Australian Context
In Australia, shoulder imaging follows a stepwise approach beginning with plain radiographs, which are widely available and the standard first-line investigation for all shoulder presentations. MRI and ultrasound are both commonly used for rotator cuff assessment, with the choice often influenced by local expertise, availability, and patient factors. Ultrasound is widely used by Australian musculoskeletal radiologists and provides a cost-effective, dynamic assessment of the rotator cuff.
MR arthrography is performed in specialist radiology centres and is the investigation of choice for shoulder instability workup in Australian orthopaedic practice. CT with three-dimensional reconstruction for glenoid bone loss quantification is standard preoperative planning for recurrent instability requiring surgical intervention. Australian orthopaedic surgeons commonly request both MRA and CT arthrography in the instability workup.
RANZCR provides guidelines for appropriate imaging requests, and Australian radiologists report shoulder imaging using standardised reporting templates that include specific assessment of the rotator cuff (tear size, retraction, fatty infiltration), labrum, biceps tendon, and acromial morphology.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
"A 60-year-old woman presents with a 6-month history of progressive shoulder pain and weakness in external rotation. Her AP radiograph shows an acromiohumeral distance of 5mm."
"A 22-year-old soldier has had three anterior shoulder dislocations. His MRI shows a Bankart lesion. An examiner asks what additional imaging you need for surgical planning."
"An examiner asks you to compare MRI, ultrasound, and MR arthrography for the assessment of rotator cuff pathology."
Shoulder Imaging -- Exam Day Reference
High-Yield Exam Summary
Radiographic Views
- •Trauma MINIMUM: AP + axillary lateral (confirms dislocation)
- •Hill-Sachs: best on AP internal rotation
- •Bony Bankart: best on axillary lateral or West Point view
- •True AP (Grashey): best for joint space assessment
- •AHD less than 7mm = massive cuff tear with superior migration
ABCS Systematic Reading
- •Alignment: GH congruence, AC joint alignment, dislocation
- •Bones: cortical outline (fractures), tuberosities, Hill-Sachs
- •Cartilage spaces: GH joint space, AHD, AC joint
- •Soft tissues: calcification, swelling, periosteal reaction
Advanced Imaging Selection
- •MRI: gold standard for cuff assessment, comprehensive evaluation
- •USS: equivalent to MRI for full-thickness tears, dynamic, cheaper
- •MRA: gold standard for labral tears (92% sensitivity) and partial cuff tears (83%)
- •CT three-dimensional: glenoid bone loss quantification (more than 20-25% = Latarjet)
- •CT arthrography: MRI alternative + bone detail
Key MRI Measurements
- •Goutallier fatty infiltration: 0-4 (3-4 = irreversible, poor prognosis)
- •Patte retraction: Stage 1 (at footprint), 2 (humeral head), 3 (glenoid)
- •Critical shoulder angle: more than 35 = cuff tear risk, less than 30 = OA risk
- •Bigliani acromion: Type I flat, II curved, III hooked (impingement risk)