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Diagnosis Of Subscapularis Rotator Cuff Tears


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.

Osteoarthritis of the shoulder is considered a degenera- tive condition of the articular cartilage.  It may be asso- ciated with inflammatory changes of the joint, but the damage  to  the  cartilage   is  not  primarily  based  on  an inflammatory pathologic process as it is for rheumatoid  arthritis.  The  rotator  cuff  tendons  are  almost  always intact in patients with  osteoarthritis, and there is a pro- liferative osteophyte formation around the periphery of the  humeral head, making it much larger than normal. The  joint  enlargement  and  flattening  of  the   humeral head  results  in  loss  of  motion.  There  is  loss  of  the uniformly white articular  cartilage on the surface of the humeral head, and there is proliferation of bone (osteo- phyte)  along the periphery of the humeral head. The head becomes flattened and larger, sometimes resem-  bling a mushroom. In most cases of osteoarthritis, the humeral head is well centered within the  center of the glenoid in anteroposterior radiographs. This is defined as the center of the humeral  head being close to the midline of the center of the glenoid. Another method of assessing this  alignment is a smooth and continuous scapulohumeral line at the inferior part of the humeral neck  (Maloney line). This is a result of an intact rotator cuff. A continuous Maloney line is not seen  when the rotator cuff is damaged, as seen on the anteroposterior radiographs in rotator cuff tear  arthropathy (see Plates 1-49  and  1-50.  With  large  and  massive  rotator  cuff years there is  superior migration of the humeral head with narrowing of the subacromial space. In some cases of   more  advanced  osteoarthritis  there  is  posterior glenoid bone loss associated with posterior  translation in  the  humeral  head  that  is  best  seen  on  an  axillary radiograph or on an  axial CT scan. The more advanced pathologic  changes  are  more  difficult  to  correct  with joint  replacement.  The   clinical   findings   of   advanced   osteoarthritis  are  significant  loss  of  passive  (stiffness)  and  active (pain-related) glenohumeral motion.  Significant pain in the shoulder is typically along the anterior and post- erior  joint  line  with   deep  palpation.  Advanced-stage osteoarthritis is often treated by total shoulder arthro- plasty.  Total-shoulder arthroplasty involves osteotomy (removal) of the humeral head at the anatomic neck  (see Plates 1-1 and 1-45) and insertion of a stem down the medullary  canal  to  which  is   attached  an  anatomically  sized and positioned prosthetic humeral head. In addi- tion,  there  is  the  preparation  of  the   glenoid  bone surface to correct pathologic version and insertion of a plastic glenoid component.  After total shoulder arthro- plasty with an intact rotator cuff without severe glenoid bone loss,  there is restoration of the normal anatomic relationships  between  the  humeral  head  center  and  glenoid  center  line  on  both  the  anteroposterior  and axillary radiographs.  Nonoperative   treatment   for   early   and   midstage arthritis would include modification  activities, oral anti- inflammatory medication, and, occasionally, corticoste- roid injection (see  Plate 1-54). Visco-supplementation with high-molecular-weight hyaluronic acid (see Plate 1-54)  injected into the joint over a series of three to five injections spaced 1 week apart has been used  as an effec- tive  nonoperative  treatment  for  knee  and  shoulder  osteoarthritis.

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.