Shoulder pain is common among many athletes, however, subscapularis
muscle injuries, although infrequent, can occasionally occur, causing
complications. Direct trauma from an injury to this specific muscle-tendon structure
can commonly affect overhead athletes, such as tennis players and swimmers. Generally,
subscapularis muscle injuries and/or conditions, which manifest in the form of
weakness and inhibition, can lead to biomechanical abnormalities in the
glenohumeral joint, including poor anterior stabilization of the shoulder joint
in the shoulder of an individual.
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Anatomy of the Shoulder
The subscapularis begins on the anterior scapular, or subscapular fossa,
and introduces onto the minor tuberosity of the humerus. It is the largest of
the rotator cuff muscles and its cross-sectional area is larger than the other
three rotator cuff muscles combined; the infraspinatus, the teres minor and the
supraspinatus. The most essential functions of the glenohumeral joint are: depressor
of the humeral head; anterior stabilizer of the humeral head, which means it glides
the humeral head posteriorly relative to the glenoid fossa; and internal
rotator of the shoulder together with the powerful pectoralis major and
latissimus dorsi.
The tendon fibres combine with the anterior capsule of the shoulder, which
serve to reinforce the anterior shoulder capsule. The muscle is considered to
be less substantial as a shoulder internal rotator, as the pectoralis major and
latissimus dorsi are powerful internal rotators, and it’s therefore more
essential as a dynamic anterior stabilizer of the glenohumeral joint due to its
action in preventing anterior shear and/or glide of the humeral head.
The subscapularis has a deep connection with the long head of the biceps.
This is known as a capsuloligamentous complex that functions to stabilize the
long head of the biceps tendon in the bicipital groove. The pulley complex is
made up of the superior glenohumeral ligament, the coracohumeral ligament, and
the distal attachment of the subscapularis tendon, where it is located within
the rotator interval between the anterior edge of the supraspinatus tendon and
the superior edge of the subscapularis tendon. Subscapularis tendon injuries
may weaken the stability of the bicep. In order to maintain the biceps tendon
stabilized and in place, support of the most superior insertion point of the
subscapularis from behind the ligament and tension in the superior glenohumeral
ligament is needed. Issues with a biceps sling is a common cause and effect of
disease in many athletes, requiring the constant and effective rotation of the
shoulder, just like the cocking position during baseball pitching.
Injuries to the Subscapularis
In the case of all the rotator cuff muscles, the subscapularis can be
exposed to stress and pressure that may damage the muscle and its surrounding
tendons. Although tears to the subscapularis are not as common as tears in the
other rotator cuff, most specifically the supraspinatus, injuries to the subscapularis
can have further complications due to its anatomical position in relation to
the long head of the biceps tendon.
Isolated ruptures of the subscapularis have previously been recorded in
the literature, Gerber and Krushell 1991. A strained hyper-extension and/or an external
rotation impact on the shoulder caused by falling onto an outstretched arm, or
in rare occasions, it may be an effect of a shoulder dislocation. These types
of injuries will result in acute shoulder pain along with a pain and weakness
in internal rotation, increased range of movement into external rotation caused
and limited by pain and a weak/pathological ‘lift-off’ test.
Direct trauma resulting in injuries to the subscapularis tendon may also
result among athletes or during occupations which require a lot of powerful
shoulder internal rotations, such as baseball pitching, tennis and swimming.
Overusing these set of muscles and their respective tendons may develop a
strain within the tendon that may not properly heal, resulting in fibrosis and
fatty tissue deposition in the tendon. Trigger points in the muscle may then
create muscle tightness and weakness.
During these cases, pain is frequently experienced as a deep anterior
shoulder pain, generally aggravated by overhead internal rotation movements,
such as serving and swimming, weakness during the ‘lift-off’ test and also,
reduced range of passive external rotation when the arm is placed by the side
is noted.
Finally, a local muscle imbalance at the shoulder between the
subscapularis and the infraspinatus may often cause issues with the position of
the head of the humerus, especially where the humeral head is not in the center
of the glenoid fossa and an extreme anterior shear of the humeral head can
often cause an impingement along with a feeling of instability in the shoulder.
The Role of the Subscapularis for Shoulder Stability
It was previously recorded that in a forceful throwing action which used quick shoulder
external rotation, individuals with shoulder injuries and/or conditions had a
delayed beginning when executing the subscapularis during external rotation
compared to the supraspinatus and infraspinatus. However, in normal shoulders
that presented no symptoms, the subscapularis was activated earlier and before
the shoulder started to externally rotate, evidence that the subscapularis works
fast-forwardly to achieve movement as well as contract earlier than movement to
provide anterior shoulder stability.
It is therefore suggested that individuals with shoulder pain lose part
of the functions which stabilize the shoulder, and as a result, the humeral
head may glide and tear the glenohumeral joint, leading to anterior shoulder
impingements.
Moreover, strength imbalances between the subscapularis and the
externally rotating infraspinatus may develop complications in the glenohumeral
joint. It is normal for the shoulder of an athlete to have a tight and
overactive infraspinatus in relation to the subscapularis. This unevenness in
the shoulder can create further issues, by which the infraspinatus tightness
caused by over activity, pushes the humeral head forward in relation to the
glenoid, and the weak and restricted subscapularis cannot correct this anterior
shear effect. As a result, the humeral head shears forward and impinges the
anterior shoulder structures, causing pain.
Clinical testing for subscapularis strength/ function
Lift-off sign
In 1991, Gerber and Krushell developed a new test for the subscapularis
muscle called a lift-off test. During this test, the hand is placed on the
lower back using a full shoulder internal rotation and the individual is asked
to lift the hand away from the back. Not being able to perform this function
may indicate weakness and/or the presence of a rupture in this muscle.
The challenge with this test is that individuals are believed to be able
to perform this fully internally rotation of the arm to place the hand behind
the back when, in reality, acutely injured shoulders will have difficulty
performing this simple motion.
Napoleon Sign/Belly Press Sign
With this next test, the individual places their hand on the stomach
with the elbow flexed 90 degrees, keeping the wrist and elbow in a straight
line. The individual is then asked to press into their stomach. If the wrist
flexes to compensate for the movement, the test is considered positive for a
weak subscapularis.
Belly Off Sign
This test is performed by having the
individual’s arm be placed in
flexion and maximum IR with the elbow flexed at 90 degrees. The examiner will
then hold the elbow while positioning the hand on the abdomen. The individual
is advised to maintain the position while the wrist remains straight as the
examiner lets go of the hand. If the hand lifts off the stomach during this
process, this is indicative of a subscapularis tear. The positioning of this
test is identical to the belly press sign test.
Bear Hug Test
In this particular test, the hand is placed on the opposite shoulder
with the elbow anterior to the body. The examiner will then apply an external
rotation force while the individual attempts to maintain the hand on the
shoulder. The test is positive if the individual is unable to hold the hand on
the shoulder as the examiner applies the external rotation force.
Subscapularis Strengthening
Only in rare cases does the subscapularis need direct stretching and
trigger point therapy to manage tightness and other symptoms caused by over
activity. It is more common for the subscapularis to need direct strengthening
exercises to help control the movement of the humeral head and stabilize the
humeral head into the glenoid fossa.
Below are some frequent exercises that may assist in strengthening the
subscapularis.
Short Range Internal Rotation
With the arm placed in a “stop sign” position, this exercise is
performed by having the individual place a band around the wrist which is
attached somewhere behind the body at shoulder height. Note: the band around
the wrist eliminates the tendency to flex the wrist and create movement. The
individual is also instructed to touch the pectoralis major and the latissimus
dorsi with the free hand to ensure that contraction in these muscles is minimized.
The individual is then instructed to internally rotate the shoulder only a few
degrees. This can be performed as a quick back and forth movement. The
individual can work on multiple sets of a few repetitions, about 10 sets of 10
repetitions.
The arm can also be placed in a forward flexed position with the elbow
in front of the shoulder. This provides an alternative joint angle for the
subscapularis to work through. This exercise is performed in a similar manner
to the “stop sign” position.
Belly Press Exercises
This is a similar exercise as described in the belly press test. Again
the individual’s opposite hand is used to touch the pec major and latissimus
dorsi. The band is again placed around the wrist not held in the hand. The individual
then performs small range internal rotation movements similar to the short
range exercise described as above, about 10 sets of 10 repetitions.
Iso-integration of Subscapularis into Pushing Movements
These exercise are made to accommodate the isolated contraction of the
subscapularis into a functional movement such as shoulder press and/or bench
press. A band or cable is held in the hand so that the direction of pull has an
external rotation direction on the shoulder. The subscapularis will then need
to contract to prevent the external rotation from occurring.
The individual should subsequently perform the general pressing movement
of a shoulder bench press while holding the cable or tubing. The individual may
perform the standard three sets of 10 repetitions while holding the band or cable.
It is important that the degree of pull from the band or cable is only
minimal. If too much force is applied on the cable or there is too much tension
on the band, an excessive external rotation turn is created which may engage
the more powerful pec major and/or latissimus dorsi to control the external
rotation twist.
Iso-integration using a dumbbell shoulder press
Iso-integration using a dumbbell bench press (start position)
Iso-integration using a dumbbell bench press (finish position)
In conclusion, research demonstrates that the subscapularis
muscle plays an essential role in providing anterior glenohumeral joint
stability. It’s the middle point of the humeral head along the glenoid during functional
movements of the arm and shoulder. Injuries or disorders in this muscle may
lead to excessive shearing and gliding of the humeral head that may be a
precursor to the more serious shoulder impingements and shoulder instabilities.
It is important for the healthcare professional to detect dysfunction in
this muscle through a number of tests and direct strengthening exercises will
be required to fully rehabilitate function on this muscle.
Whole Body Wellness
By Dr. Alex Jimenez
