Diagnosis Of Subscapularis Rotator Cuff Tears
Subscapularis tears can be isolated to the subscapularis tendon or can be associated with tears involving the superior and posterior portions of the rotator cuff. MRI can show the subscapularis muscle belly passing under the coracoid and then attaching to the lesser tuberosity. With the location of the subscapularis muscle being posterior to the chest wall, its most significant function in internal rotation is seen with the arm closest to the body. Therefore, the function of the subscapularis muscle and its associated tendon is most responsible for the internal rotation function of the shoulder, particularly internal rotation strength near the center of the body. This important function specific to the subscapularis results in defining the most sensitive physical examination tests for weakness associated with this part of the rotator cuff. The other large internal rotator muscles (i.e., pectoralis major, latissimus dorsi, and pec- toralis minor) also provide internal rotation strength to the shoulder but provide most of the strength to the shoulder when the arm is away from the body. For these reasons the best method of testing for subscapularis function is to test internal rotation strength close to the trunk rather than away from the body. The abdominal compression test or internal rotation lag sign are the two best methods for testing subscapularis function. Most subscapularis tendon tears will be missed on phys- ical examination if these specific subscapularis tests are not performed, and internal rotation strength is tested in various degrees of abduction and external rotation because the other internal rotators of the shoulder are so strong that the less specific physical examination tests will not show weakness by manual muscle testing. The abdominal compression test demonstrates the inability to internally rotate the arm with the hand against the abdomen with or without resistance to internal rotation. When performing this test, it is critical to be sure that the patient keeps the palm of the hand completely against the abdomen. Elevation of the palm off of the abdomen to achieve some internal rotation of the shoulder is a sign of weakness of the subscapularis. In addition, demonstrated weakness in a true positive abdominal compression test (positive means weakness and inability to fully perform the test) must be accompanied by the examiner demonstrating the ability to passively achieve full internal rotation by the examiner passively lifting the elbow and achieving full passive internal rotation. This is necessary to rule out loss of motion secondary to shoulder stiffness, which will give a false-positive result of the abdominal compression test.
Another test for subscapularis function is the lift-off or internal rotation lag sign. This test is more difficult for many patients to do because of shoulder pain, and it requires good passive range of motion and normal elbow function. For these reasons, this test is not always performed in patients with larger rotator cuff tears. This test is more sensitive to define minor weakness of the rotator cuff associated with smaller or partial tears, and in these cases most patients are able to perform this test. A positive lift-off or internal rotation lag sign is defined by the patient’s inability to lift the hand off of the buttock. In addition to a loss of active internalrotation, there is an increase in passive external rotation because of loss of the continuity of the subscapularis muscle and tendon to the lesser tuberosity. In this case, increased passive external rotation is easily seen when the patient is placed in the supine position and each shoulder is passively externally rotated and compared. Acute traumatic full-thickness subscapularis tears are best treated by early diagnosis, which is best done by physical examination. With subscapularis tendon tears there is often damage to the long head of the biceps.
This subscapularis tendon tear is associated with a dislocation in the long head of the biceps tendon from the biceps groove. Repairs can be done by either open or arthroscopic suture technique. The principles and methods of repair are the same as those described for supraspinatus and infraspinatus tears. Long head of the biceps damage or dislocation is treated by release of the long head of the biceps or tenodesis of the tendon, as described i the discussion of pathologic processes of the biceps.