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SASD Bursa
The SASD bursa is a large bursa that separates deltoid from the rotator cuff tendons. Impingement synptoms occur when there is inflammation of the bursa usually due to loss of subacromial space. This can occur for complex reasons including:
  • Genetic predisposition
  • Scapular re-orientation due to muscle imbalance (Sick Scapula)
  • Bony impingement related to AC shape and osteophytes
  • Enlarged tendon due to tendinopathy
Of these, the biomechanical causes are the more important. Bony abnormalities unless gross are thought to be less significant.In time the supraspinatus tendon is also affected and may become tendinopathic.

Bursitis may have normal imaging. In more advanced cases, fluid and synovial thickening. Marked fluid and synovitis is usually more indicative of a local or systemic inflammatory process rather than singement.

MRI is less reliable in the diagnosis of tendinopathy. The signs described include signal alteration with loss of the normal low signal on T1 weighted images, diffuse increase signal on T2 weighted images and alterations in tendon dimension. A wide inter and intra observer variation has been described with all of these. This is particularly the case with signal alterations on T1 weighted images. Similar alteration can be seen with variation in muscle tendon interdigitation and signal changes induced by the magic angle phenomenon. The latter are particularly problematic on short TE images.
Bursal fluid and supraspinatus tendinopathy
Supraspinatus tendinopathy
Coronal US. Bunching of the SASD bursa on abduction
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Fluid distending SASD bursa. Also note fluid and synovial thickening in the biceps sheath
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