What is the best imaging modality to rule out shoulder impingement?

Best Imaging for Shoulder Impingement

MRI without contrast is the best imaging modality to rule out shoulder impingement syndrome, providing excellent visualization of soft tissue structures including the rotator cuff, subacromial bursa, and surrounding anatomy. 1

Imaging Algorithm for Shoulder Impingement

Initial Imaging

• Plain radiographs should be performed first as the initial imaging study for any shoulder pain to evaluate for bony abnormalities and alignment issues 1
• Standard radiographic views should include anteroposterior views in internal and external rotation and an axillary or scapula-Y view 1
• Radiographs can identify structural causes of impingement such as acromial spurs, acromioclavicular joint hypertrophy, or abnormal acromial morphology 1

Secondary Imaging (After Normal/Nonspecific Radiographs)

MRI Without Contrast

• MRI without contrast is generally considered the best modality for adequately assessing most soft tissue injuries, including rotator cuff pathology 1
• MRI provides excellent visualization of:
  • Supraspinatus tendinitis or tears 2
  • Subacromial bursitis 2
  • Muscle atrophy and fatty infiltration 3
  • Bone marrow edema 1
  • Other associated soft tissue injuries 1
• MRI has high sensitivity and specificity for detection of full-thickness rotator cuff tears 1
• The American College of Radiology gives MRI without contrast a 9/9 appropriateness rating for evaluating rotator cuff pathology 3

Ultrasound

• Ultrasound is an alternative with high sensitivity and specificity for detecting full-thickness rotator cuff tears (90-91% sensitivity, 93-95% specificity) 1
• Ultrasound has the advantage of being dynamic, non-invasive, and less expensive 4
• The American College of Radiology rates ultrasound equally appropriate (9/9) as MRI for evaluating rotator cuff integrity when performed by experienced operators 3
• Ultrasound has limitations:
  • Operator-dependent results 1, 4
  • Limited evaluation of partial-thickness tears 1
  • Cannot adequately assess other intra-articular pathologies 1
  • Limited in patients with large body habitus or restricted range of motion 1

MR Arthrography

• MR arthrography has increased sensitivity for detection of partial-thickness articular surface tears compared to conventional MRI 1
• It is considered the gold standard for imaging traumatic shoulder pain 1
• However, its invasive nature makes it a suboptimal initial study 1
• In acute settings, a post-traumatic joint effusion may provide sufficient visualization of soft tissue structures on standard MRI, making arthrography unnecessary 1

Clinical Considerations

• MRI is preferred when there is suspicion of other intra-articular pathologies such as labral tears 1
• Ultrasound may be preferred in cases with previously placed proximal humeral hardware that would limit MRI examination due to susceptibility artifacts 1
• CT is generally not recommended for evaluation of shoulder impingement as it is inferior to MRI for diagnosing soft tissue injuries 1
• MRI can identify several abnormalities associated with impingement syndrome that may not be visible on other imaging modalities:
  • Compression of the supraspinatus tendon and/or subacromial bursa by spurs 2
  • Capsular hypertrophy of the acromioclavicular joint 2
  • Low-lying acromion 2
  • Tendinitis versus small tears (differentiated on T2-weighted imaging) 2

Pitfalls and Caveats

• Relying solely on imaging without clinical correlation may lead to overdiagnosis, as asymptomatic rotator cuff tears are common in older populations 5
• T2-weighted MRI sequences are necessary to differentiate tendinitis from small tears of the supraspinatus tendon 2
• Ultrasound results vary significantly based on operator experience 4
• Complete evaluation should include assessment of all rotator cuff tendons, as isolated supraspinatus tendon injury is most common but may occur in conjunction with other rotator cuff tendon injuries 5