interpreting-musculoskeletal-imaging

# Interpreting Musculoskeletal Imaging

Structures MSK imaging interpretation with fracture classification and joint assessment protocols.

## Why This Skill Exists

Musculoskeletal imaging represents approximately 30% of all radiology studies, spanning radiographs, CT, MRI, and ultrasound. Missed fractures — particularly scaphoid, femoral neck, and posterior malleolus — are among the top malpractice claims in emergency radiology. Orthopedic surgeons rely on precise fracture classification systems (Neer, Weber, Garden, Schatzker, AO/OTA) to determine surgical vs. conservative management. Internal derangement assessment on MRI requires systematic evaluation of ligaments, tendons, menisci, and cartilage using validated grading systems.

The ACR Practice Parameter for Musculoskeletal Imaging requires structured reporting that includes fracture classification when applicable, joint alignment assessment, and correlation with clinical mechanism of injury. Failure to describe fractures using surgeon-expected classification systems creates communication gaps that can delay appropriate treatment. This skill enforces systematic MSK interpretation with standardized classification and grading systems used by orthopedic surgeons and sports medicine physicians.

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## Checkpoint A: Pre-Draft Intake (Mandatory)

1. **What body part and laterality?** (Default: Verify from order — laterality errors are sentinel events)
2. **What modality?** (Default: Radiograph — specify CT, MRI, or US)
3. **What is the clinical indication?** (Default: Trauma, pain, post-operative — obtain specific mechanism)
4. **Is this a trauma or non-trauma study?** (Default: Trauma — determines classification system)
5. **Are prior studies available?** (Default: No priors)
6. **Is the patient pediatric (<18)?** (Default: Adult — pediatric requires growth-plate assessment)
7. **Is this a post-operative evaluation?** (Default: No — if yes, obtain operative note)
8. **Are weight-bearing views obtained (if applicable)?** (Default: Verify for knee, ankle, foot)

### Documents to Request

- Current imaging study (all views/sequences)
- Prior imaging of the same body part
- Requisition with mechanism of injury and clinical question
- Operative notes if post-surgical evaluation
- Relevant clinical exam findings (instability, point tenderness, ROM)
- For MRI: prior arthroscopy or surgical reports

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## Step 1: Radiograph Interpretation — Systematic Approach

Use the "ABCDs" mnemonic for every MSK radiograph:

**A — Alignment**
- Joint congruency and articular surface relationships
- Angular deformity (varus/valgus, anterior/posterior angulation)
- Displacement measurement (mm and percentage of bone width)
- Subluxation or dislocation

**B — Bone**
- Cortical integrity: fracture lines (transverse, oblique, spiral, comminuted)
- Bone density: osteopenia, lytic lesions, blastic lesions
- Periosteal reaction: solid, lamellated, sunburst, Codman triangle
- Bone infarcts, enchondromas, fibrous cortical defects

**C — Cartilage and Joint Space**
- Joint space narrowing (uniform vs. non-uniform)
- Osteophyte formation
- Subchondral sclerosis and cysts
- Chondrocalcinosis

**D — Soft Tissues**
- Joint effusion (fat pad signs: sail sign in elbow, suprapatellar)
- Soft-tissue swelling localization
- Foreign bodies
- Calcific tendinopathy, myositis ossificans

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## Step 2: Fracture Classification Systems

### Upper Extremity

| Fracture | Classification | Surgical Implication |
|----------|---------------|---------------------|
| Proximal humerus | **Neer** (2, 3, 4 part based on displacement >1 cm or angulation >45°) | ≥3 parts usually surgical |
| Clavicle | **Allman/Robinson**: Group I (middle third), II (lateral), III (medial) | Lateral third with CC ligament disruption = surgical |
| Distal radius | **Frykman** (I–VIII based on intra-articular involvement and ulnar styloid) | Intra-articular + displacement = surgical |
| Scaphoid | **Herbert** (A = stable, B = unstable; B1-proximal pole highest AVN risk) | Proximal pole or displaced >1 mm = surgical |

### Lower Extremity

| Fracture | Classification | Surgical Implication |
|----------|---------------|---------------------|
| Femoral neck | **Garden** (I-IV: incomplete to complete displacement) | Garden III-IV = arthroplasty in elderly |
| Intertrochanteric | **Evans/AO**: stable vs. unstable patterns | Unstable patterns require intramedullary fixation |
| Tibial plateau | **Schatzker** (I–VI: lateral split to bicondylar) | Articular depression >3 mm typically surgical |
| Ankle | **Weber** (A = below syndesmosis, B = at, C = above) | Weber C = syndesmotic injury = surgical |
| Calcaneus | **Sanders** (I–IV based on CT coronal through posterior facet) | Type III-IV = surgical |

### Spine

| Fracture | Classification | Stability |
|----------|---------------|-----------|
| Cervical burst | **AO Spine**: A0–C with neurologic modifier | Type B/C = unstable |
| Thoracolumbar | **TLICS**: mechanism + posterior ligament + neurologic status | Score ≥5 = surgical |
| Odontoid | **Anderson and D'Alonzo**: Type I (tip), II (base), III (body) | Type II = highest nonunion risk |

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## Step 3: MRI Internal Derangement — Joint-Specific Protocols

### Knee MRI Systematic Review

| Structure | Grading System | Key Findings |
|-----------|---------------|-------------|
| ACL | Intact / partial tear / complete tear | Increased signal, discontinuity, laxity; secondary signs: bone bruise pattern (lateral femoral condyle + posterior tibial plateau) |
| PCL | Intact / partial / complete | Increased signal, thickening; bucket-handle pattern if avulsed |
| Meniscus | Grade 1 (globular signal) / Grade 2 (linear signal not reaching surface) / Grade 3 (signal reaching articular surface = tear) | Only Grade 3 = surgical tear |
| MCL | Grade I sprain / Grade II partial / Grade III complete | Periligamentous edema, fiber discontinuity |
| Cartilage | Modified Outerbridge: Grade I (softening), II (partial thickness <50%), III (>50%), IV (full thickness/bone exposed) | Location by compartment |
| Bone marrow | Edema pattern: traumatic vs. stress vs. degenerative | Subchondral location and distribution |

### Shoulder MRI Systematic Review

| Structure | Key Assessment |
|-----------|---------------|
| Rotator cuff | Supraspinatus, infraspinatus, subscapularis, teres minor: tendinopathy vs. partial vs. full-thickness tear; retraction grade |
| Labrum | Superior (SLAP I–IV), anterior (Bankart), posterior labral tears |
| Biceps tendon | Long head: subluxation, dislocation, tear; pulley lesions |
| Acromioclavicular joint | Osteoarthritis, capsular hypertrophy, impingement |
| Subacromial space | Subacromial-subdeltoid bursal fluid, impingement |

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## Step 4: Report Structure

### Findings Section Organization
1. **Alignment** — joint congruency, fracture displacement
2. **Osseous structures** — fractures with classification, marrow signal
3. **Ligaments/Tendons** — integrity, grading
4. **Menisci/Labrum** — tear type, location
5. **Cartilage** — grade, location, extent
6. **Soft tissues** — effusion, bursitis, masses
7. **Hardware** (if post-op) — position, loosening, periprosthetic fracture

### Impression
- Numbered, most clinically significant first
- Fracture classification stated (e.g., "Weber B fibula fracture with deltoid ligament injury")
- Surgical relevance of findings highlighted
- Follow-up recommendations with modality and timing

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## Step 5: Pediatric-Specific MSK Considerations

| Finding | Assessment |
|---------|-----------|
| Salter-Harris fracture | Type I (through physis), II (physis + metaphysis, most common), III (physis + epiphysis), IV (all three), V (crush) |
| Growth plate | Open vs. partially fused vs. closed; asymmetry with contralateral side |
| Apophyseal avulsion | Ischial tuberosity, AIIS, ASIS, iliac crest — common in adolescent athletes |
| Toddler's fracture | Subtle spiral tibial fracture; may require oblique views |
| Non-accidental trauma | Metaphyseal corner fractures, posterior rib fractures, multiple fractures of different ages — mandatory reporting |

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## Checkpoint B: Post-Draft Alignment (Mandatory)

1. Is laterality correctly stated and verified against the order?
2. Are fractures classified using the appropriate surgeon-expected system?
3. Is displacement quantified (mm and percentage)?
4. Are MRI ligament/tendon findings graded?
5. Are critical findings (e.g., NAT patterns in pediatrics) flagged for communication?

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## Quality Audit

- [ ] Laterality is explicitly stated and matches the requisition
- [ ] All views/sequences are systematically reviewed (ABCDs for radiographs)
- [ ] Fractures are classified using the appropriate named system
- [ ] Displacement and angulation are quantified
- [ ] Joint alignment is assessed
- [ ] MRI internal derangement uses validated grading systems
- [ ] Meniscal tears are graded (only Grade 3 = surgical tear)
- [ ] Rotator cuff tears specify full vs. partial thickness and retraction
- [ ] Effusion and soft-tissue findings are documented
- [ ] Hardware position is assessed in post-operative studies
- [ ] Pediatric growth plates are evaluated when applicable
- [ ] Comparison with prior studies documents interval change
- [ ] Critical findings (NAT, vascular injury, compartment syndrome) trigger immediate communication
- [ ] Impression includes surgical relevance of findings

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## Guidelines

1. Always verify laterality before interpretation — laterality errors are reportable sentinel events.
2. Use the fracture classification system expected by the surgical subspecialty (e.g., Schatzker for tibial plateau, not just "comminuted fracture").
3. On knee MRI, only Grade 3 meniscal signal (reaching articular surface) represents a surgical tear — Grades 1 and 2 are intrameniscal degeneration.
4. For scaphoid fractures, if radiographs are negative but clinical suspicion is high, recommend MRI within 24–48 hours per ACR Appropriateness Criteria.
5. In pediatric trauma, always assess the growth plates (Salter-Harris classification) and compare with the contralateral side when available.
6. Document the mechanism of injury when available — it directs attention to commonly associated injuries (e.g., dashboard injury → posterior hip dislocation + posterior wall acetabular fracture).
7. Post-operative imaging requires comparison with immediate post-op films to assess hardware migration, loosening, or periprosthetic fracture.
8. Suspect non-accidental trauma in children with metaphyseal corner fractures, posterior rib fractures, or fractures of different ages — this triggers mandatory reporting obligations.