How is a rotator cuff injury diagnosed?

Diagnosing Rotator Cuff Injury

MRI is the optimal diagnostic imaging modality for rotator cuff injuries, with high sensitivity and specificity for full-thickness tears, while MR arthrography offers superior detection of partial-thickness tears. 1

Clinical Evaluation

History and Symptoms

• Pain located in the anterior or anterolateral aspect of the shoulder that worsens with overhead activities (sensitivity 88%, specificity 33%) 2
• Pain during specific phases of throwing motions (arm cocking and acceleration phases) in athletes 2
• Decreased velocity and precision in throwing athletes 2
• Pain during release, deceleration, and follow-through phases in throwing athletes 1

Physical Examination

• Decreased range of motion, particularly during abduction with external or internal rotation 1, 2
• Focal weakness in the affected shoulder (prevalence 75%) 2
• Positive special tests:
  • Neer's test (sensitivity 88%, specificity 33%) 2
  • Hawkins' test (sensitivity 92%, specificity 25%) 2
  • External Rotation Lag Sign at 90 Degrees (highest diagnostic odds ratio 12.70) 3
  • Supraspinatus weakness and weakness of external rotation (highly predictive, especially in patients over 60) 4

Diagnostic Imaging Algorithm

Initial Imaging

• Plain radiographs should be performed first to rule out fractures, dislocations, and other bony abnormalities 1

Secondary Imaging (based on clinical suspicion of rotator cuff tear)

1. MRI:

   • Best overall modality for assessing soft-tissue injuries including rotator cuff pathology 1
   • High sensitivity and specificity for full-thickness tears 1
   • Lower sensitivity for partial-thickness tears compared to MR arthrography 1

2. Ultrasound:

   • High sensitivity and specificity for full-thickness rotator cuff tears 1, 2
   • Equivalent to MRI for evaluating rotator cuff abnormalities (sensitivity 85%, specificity 90%) 2
   • Variable interobserver agreement for partial-thickness tears 1
   • Advantages: cost-effective, dynamic assessment, no contraindications 1

3. MR Arthrography:

   • Preferred for assessing intra-articular pathology 1
   • Increased sensitivity for partial-thickness articular surface tears 1
   • Best for diagnosing labral and partial-thickness rotator cuff tears 1

4. CT Arthrography:

   • Alternative when MRI is contraindicated 1
   • Similar performance to MR arthrography for full-thickness tears 1
   • Significantly poorer performance for partial-thickness tears 1

Special Considerations

Age-Related Differences

• In youth/adolescent throwers:
  • Injuries often result from atraumatic microinstability and weak rotator cuff muscles 1
  • Undersurface tears from overuse are more common than primary impingement 1
  • Secondary impingement syndrome (difficulty for humeral head to stay centered in glenoid fossa) is more common 2

Biomechanical Factors

• Scapular dyskinesis (poor coordination of scapular movements during arm elevation) contributes to rotator cuff injury 1, 2
• Muscular imbalance (weakened posterior shoulder musculature with overdeveloped anterior musculature) increases injury risk 1, 2

Common Pitfalls

• Noncontrast CT is unable to assess rotator cuff pathology in the acute setting 1
• FDG-PET/CT and bone scans are not routinely used for diagnosing rotator cuff tears 1
• Ultrasound interpretation is operator-dependent with variable interobserver agreement for partial-thickness tears 1
• Failure to distinguish between primary impingement (more common in adults) and secondary impingement (more common in younger athletes) may lead to inappropriate treatment 2

Diagnostic Approach Summary

1. Perform thorough clinical examination with specific rotator cuff tests
2. Obtain plain radiographs to rule out bony abnormalities
3. For suspected full-thickness tears: MRI or ultrasound (based on institutional preference)
4. For suspected partial-thickness tears: MR arthrography offers highest sensitivity
5. Consider CT arthrography only when MRI is contraindicated