MRI Imaging of the Shoulder:

- Discussion:
    - used to assess impingement syndromes (coronal oblique views) and less often
      glenoid pathology (transaxial views);
    - it accurately identifes full-thickness rotator cuff tears;
          - defects show up with high signal intensity traversing supraspinatus tendon on
            T2 images;
          - MRI is less specific in diagnosing tendinitis & partial tears;
    - external rotation:
          - patients should keep the shoulder in external rotation during the exam;
          - position keeps slight tension on anterior capsular structures;
          - external rotation permits maximum visualization of the supraspinatus insertion, and prevents confusing
            overlap with the infraspinatus tendon on coronal oblique images;
    - signal intensity characteristics:
          - fat suppressed T2 weighted:
                - long repitition time and long echo time
                - water gives bright signal and fat gives very dark signal;
                - allows evaluation of marrow pathology;
          - STIR images:
                - long repitition time and variable echo time;
                - water gives bright signal and fat gives very dark signal;
                - allows evaluation of marrow pathology;
          - gradient echo:
                - short repitition time and short echo time
                - intermediate fat signal and intermediate to bright water signal;
                - for evaluation of articular cartilage, blood, and PVNS;
          - proton density:
                - long repitition time and short echo time;
                - intermediate to high fat signal and intermediate water signal;
                - high resolution for evaluation of labral tears, but poor evaluation of marrow;
          - references:
                - Rotator Cuff: Evaluation with US and MR Imaging.
                - Labral injuries: accuracy of detection with unenhanced MR imaging of the shoulder.


- Specific Views:    (see Anatomy of the shoulder (MR) - Atlas of the human body)
    - transaxial view of the shoulder:
             - evaluates shoulder capsule, glenoid labrum, subscapularis, biceps and for evaluation of a Hill Sachs Lesion;
             - protocols: fat suppressed T2 wt images and proton density weighted images
    - oblique saggital
             - plane is perpendicular to supraspinatus;
             - non fat suppressed T1 wt images and fat suppressed
               T2 wt images;
             - acromial morphology is best evaluated on sagittal oblique
               magnetic resonance images;
               (see radiographic evaluation of impingement syndromee)
             - useful for imaging the subscapularis;  
             - w/ subscapularis tears look for disruption of the transverse
               ligament;
             - biceps tendon is followed from medial to lateral as it coursess
                from its intra-articular origin on supraglenoid tubercle
                to its extracapsular location in the bicipital groove laterally;

    - coronal oblique views of the MRI:  
             - protocols: fat suppressed T2 wt images and proton density weighted images

             

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- Hagl Lesion:
    - avulsion of inferior ligament from the humerus;
    - references:
          Humeral avulsion of the anterior shoulder stabilizing structures after anterior shoulder
               dislocation: demonstration by MRI and MR arthrography.
               PF Tirman et al.  Skeletal Radiology.  Vol 25(8). 1996 Nov. p 743-8.