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.
