Impingement and instability are two main categories of abnormalities causing pain in the shoulder. Physical exam can usually differentiate between these causes, but occasionally the exam signs are equivocal or may suggest a combination of these factors.
When impingement is suspected, MRI has advantage over conventional arthrograms by visualizing the extent of rotator cuff abnormality and contributing bony / anatomic features. Decisions regarding conservative or surgical treatment, or the particular surgical approach can be affected by the findings at MRI.
When instability is suspected, a tear of the glenoid labral cartilage or the supporting glenohumeral ligaments may be the cause. The intra-articular contrast and joint distention achieved with MR arthrography significantly improves the accuracy in the detection and characterization of these tears, and is the preferred imaging modality.
Injection of a dilute contrast material into the shoulder is performed under x-ray (fluoroscopic guidance). Then, MR imaging is performed. Additional sensitivity for the detection of labral tears is gained when imaging in the ABER (abducted, externally rotated) position is performed. ABER positioning stresses the anterior supporting structures, revealing tears sometimes not apparent on images obtained in a neutral position. Tirman was the first to demonstrate this.
Because of these advantages, we attempt imaging in the ABER position in all patients.
Case 1: Anterior and posterior labral tears. Paralabral cysts. Anterior labral tear seen only with ABER views.
SLAP tears of the superior labrum may be difficult to detect at physical exam. These increasingly recognized superior labral tears classically occur in throwing athletes. However, a wider variety of mechanisms and patient presentations in combination with high quality MR arthrographic technique have increased the awareness and diagnosis of SLAP tears.
Case 2: SLAP tear, superior labrum