Imaging Modalities 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, as recommended by the American College of Radiology 1, 2
Standard radiographic views should include anteroposterior views in internal and external rotation and an axillary or scapula-Y view, according to the American College of Radiology 2
Radiographs can identify structural causes of impingement such as acromial spurs, acromioclavicular joint hypertrophy, or abnormal acromial morphology, with a high degree of accuracy 2, 3

MRI without contrast is generally considered the best modality for adequately assessing most soft tissue injuries, including rotator cuff pathology, with high sensitivity and specificity 1, 4
MRI provides excellent visualization of muscle atrophy and fatty infiltration, bone marrow edema, and other associated soft tissue injuries, as stated by the American College of Radiology 4, 5
The American College of Radiology gives MRI without contrast a 9/9 appropriateness rating for evaluating rotator cuff pathology, indicating strong evidence 5

Ultrasound is an alternative with high sensitivity and specificity for detecting full-thickness rotator cuff tears, with a sensitivity of 90-91% and specificity of 93-95%, as rated by the American College of Radiology 1, 4
The American College of Radiology rates ultrasound equally appropriate (9/9) as MRI for evaluating rotator cuff integrity when performed by experienced operators, indicating strong evidence 5
Ultrasound has limitations, including operator-dependent results and limited evaluation of partial-thickness tears, as noted by the American College of Radiology 4, 2, 6

MR arthrography has increased sensitivity for detection of partial-thickness articular surface tears compared to conventional MRI, and is considered the gold standard for imaging traumatic shoulder pain, as stated by the American College of Radiology 1, 4, 6

MRI is preferred when there is suspicion of other intra-articular pathologies such as labral tears, due to its high sensitivity and specificity 4
Ultrasound may be preferred in cases with previously placed proximal humeral hardware that would limit MRI examination due to susceptibility artifacts, as noted by the American College of Radiology 4
CT is generally not recommended for evaluation of shoulder impingement as it is inferior to MRI for diagnosing soft tissue injuries, according to the American College of Radiology 2, 6

The American College of Radiology rates ultrasound as "usually appropriate" (9/9 rating) for rotator cuff assessment, with excellent accuracy when performed by experienced operators 7
Ultrasound has important limitations, including difficulty in detecting partial-thickness tears and limited evaluation of deep structures such as labral tears, capsular structures, and bone marrow pathology 7
The reliability of ultrasound for shoulder ligament ruptures is less established compared to tendons 7

The American College of Radiology recommends ultrasound as the first-line soft tissue imaging modality for evaluating suspected full-thickness rotator cuff tears in experienced hands 7
Ultrasound is appropriate for assessing biceps tendon pathology 7
Ultrasound is preferred for guiding therapeutic injections or aspirations 7, 8
MRI without contrast is preferred over ultrasound for patients under 35 years old with suspected instability and labral pathology 7, 8
MRI has superior sensitivity for incomplete tendon injuries, such as suspected partial-thickness tears 7

The American College of Radiology advises against relying on ultrasound alone for partial tears, as these require MRI or MR arthrography for accurate diagnosis 7
MRA is the gold standard for labral pathology, and ultrasound should not be used for suspected labral injuries 7
It is essential to verify local expertise before relying on ultrasound results, as operator dependency affects diagnostic accuracy 7
Initial radiographs should always be obtained to exclude fractures and dislocations before using ultrasound 8