Tendinitis and rupture also can involve the subscapularis, infraspinatus, and teres minor, or biceps tendons, although far less commonly than the supraspinatus. Early tendinitis involves an increased signal intensity area within the tendon. This can progress to frank rupture of the tendon with a high–signalintensity area at the site of the tear on T2-weighted images and may be associated with joint effusion. A complete tear will eventually cause muscle retraction and later atrophy.
Calcific tendinosis (Fig. 6-8) of the supraspinatus is a common clinical entity most commonly affecting middle age persons. It is slightly more common in females and can affect multiple tendons in the body. It is however far more frequently in the supraspinatus. Although the exact etiology is unknown, it is felt to be secondary to chronic ischemia of the tendon fibers.
FIGURE 6-8. Calcific tendinosis of the infraspinatus tendon. A: Axial T1WI and B: coronal oblique T2WI with fat suppression demonstrating a focal area of decreased signal within the fibers of the distal infraspinatus (arrow). Note high–signal-intensity fluid within the posterior joint (*). C: Sagittal oblique T1WI shows the calcification within the posterior fibers of the infraspinatus.
Increased high-intensity fluid about the biceps tendon on T2-weighted MR images can be produced by either a biceps tenosynovitis or a shoulder joint effusion because the tendon sheath normally communicates with the shoulder. Rupture of the biceps tendon is demonstrated by absence of the biceps tendon within the intertubercular sulcus and by distal retraction of the muscle, which is seen on imaging the arm (16). Dislocation of the biceps tendon is identified by medial displacement of the biceps tendon out of the intertubercular sulcus.