While rotator cuff impingement is very common, injury to the | Figure 1

Pomeranz

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While rotator cuff impingement is very common, injury to the myotendinous junction and muscle belly of the supraspinatus is not common. This case demonstrates an intermediate-grade tear of the muscle belly and myotendinous junction of the supraspinatus with minimal interstitial tearing extending into the supraspinatus tendon (images 8 and 9; red arrows). The unusually medial location of these injuries within the supraspinatus myotendinous unit indicates that the focus of impingement lies more medial than the usual subacromial location. Consistent with this, the acromioclavicular joint demonstrates marked active-on-chronic arthropathy (image 7; yellow arrows), with inferior hook-shaped spurs (image 6; green arrows) resulting in medial arch stenosis.

Although the epicenter of the injury to the supraspinatus does not immediately abut the acromioclavicular joint, impingement is a dynamic problem, and the acromioclavicular spurs likely impact upon the supraspinatus during various shoulder movements and in different postures.

The myotendinous junction tear (images 8 and 9; red arrows) extends as small interstitial tears (image 10; blue arrows) into the supraspinatus tendon.

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