Imaging Of Supraspinatus And Infraspinatus Rotator Cuff Tears
The rotator cuff tendons surround the humeral head and are attached to the lesser tuberosity (subscapularis) and the greater tuberosity (supraspinatus and infraspinatus tendons and teres minor). Between the two tuberosities is the bicipital groove through which is the long head of the biceps tendon (see Plate 1-4).
Rotator cuff tears can be either partial or full thick- ness. Partial-thickness tears involve only a superficial surface of the tendon and may extend into the tendon substance but are not through-and-through defects. A full-thickness defect involves the full thickness of the tendon and may involve more than one tendon.
Tendon tear size is defined as either partial thickness or full thickness and is also defined by the size in centimeters of involvement as well as the tendons involved (e.g., supraspinatus, infraspinatus). When a large tendon tear is present, often involving more than one tendon such as the supraspinatus and infraspinatus, there is retraction of the tendon from its insertion site. When a tear is present for a substantial period of time, the muscle tissue in the area of the involved tendons undergoes muscular atrophy and fatty infiltration. These changes are often seen on MR images and are important prognostic factors with respect to the ability of the tendon to be repaired or the potential for healing of the repaired tendon. Larger tears result in loss of both active forward flexion and external rotation.
Imaging of the rotator cuff can include ultrasonography, MRI, and CT. Ultrasonography provides a simple and cost-effective means of assessing the presence of a both partial and full-thickness tears of the rotator cuff. The efficacy of ultrasonography is improved with dynamic assessment and recording of the images and should be done by an experienced radiologist. Many health care systems have not developed the same expertise with the use of ultrasound when compared with CT arthrography or MRI with or without the use of contrast enhancement of the images. Contrast arthrography is performed by injection of a liquid contrast material into the glenohumeral joint. When there is a full-thickness tear of the rotator cuff, the contrast material will leak out of the joint through the defect in the rotator cuff and be seen on plain radiographs, CT scans, or MR images as fluid in the subacromial space. Use of plain radiographs will give a two-dimensional view of the shoulder; but when taken in multiple planes, radiographs can give a more clear definition of the size and location of the tear. Much more information is available with thin slice tomographic imaging available with CT and MRI. In addition, an assessment of the muscle atrophy and amount of fatty infiltration of the muscle can been seen with CT and MRI. For most clinicians, MRI is preferred as the study providing the most information related to cuff tear size, location of the tear, degree of tendon retraction, and the changes in the muscle associated with the location of the tear.