Tracy Ward explores the subject of shoulder instability; what preventative measures can athletes take to prevent its occurrence or worsening? Shoulder instability is the abnormal movement of the shoulder joint beyond normal physiological ranges, which can result in subluxation (partial displacement) or dislocation (full displacement) of the humeral head in the glenoid cavity (shoulder joint... MORE
Subscapularis: the key to shoulder stability
In a previous article, Chris Mallac explored the unique anatomical and biomechanical features of the subscapularis, the common injury patterns associated with this muscle and the important role it has in shoulder stability. In this article, Chris outlines the classical signs and symptoms of subscapularis injury and provides rehabilitation ideas for injured and dysfunctional subscapularis muscles.
The subscapularis provides dynamic anterior support to the glenohumeral joint; assists the other rotator cuff muscles in centering and stabilizing the humeral head in the glenoid; and is a key anatomical component of the long head of biceps tendon pulley system.
Signs and symptoms
Tears to the subscapularis muscle and tendon are often difficult to diagnose by physical examination alone. The typical symptoms include:
- May be associated with a mechanism of injury involving forced external rotation or associated with a shoulder dislocation.
- Usually vague anterior shoulder pain.
- Pain, weakness and difficulty with shoulder flexion and internal rotation.
- Pain location and radiation is not reliable for the diagnosis of subscapularis injury.
Clinical testing for subscapularis strength/function
There are a number of clinical orthopedic tests used to diagnose injury to the subscapularis, each with their own specificity and sensitivity. Rigsby et al reviewed a number of these tests and found that the Napoleon sign, internal rotation lag sign, and lift-off index tests all demonstrated good clinical usefulness for ruling a full-thickness subscapularis tear in or out(1).
A number of the following tests can be used effectively for screening for partial-thickness subscapularis tears; however, no single test has yet demonstrated high value for clinically determining its presence (as based on sensitivity). The bear-hug test holds promise for partial-thickness tears. These tests will be discussed below. Positive findings on a number of these tests may be used to collectively determine partial injury to the subscapularis; therefore the clinician is encouraged to run a battery of clinical tests for the subscapularis.
Lift off sign (Gerber and Krushell 1991)(2)
This test was initially proposed by Gerber and Krushell in 1991(2). In the test, the hand is placed on the small of the back (full shoulder internal rotation) and the patient is asked to lift the hand away from the back (see figure 1). The test is considered positive if the patients are unable to lift the arm posteriorly off the back or if they perform the lifting maneuver by extending the elbow or the shoulder.
The difficulty with this test is that assumption is made that the patient is in a functional state whereby they can actually fully internally rotate the arm to place the hand behind the back. In acutely injured shoulders this may be difficult if not impossible to perform.
Figure 1: Lift off test/sign
Internal rotation lag sign (Hertel et al 1996)(3)
This test uses the same starting position as the lift-off sign and is therefore subject to the same limitations. The examiner passively lifts the hand away from the back to achieve maximum internal rotation. The examiner then removes the pressure and asks the patient to hold this position. Any return of the hand to the back is considered positive(3).
Napolean sign/belly press sign (Burkhart and Tehrany 2002)(4)
The patient places their hand on the belly with the elbow flexed 90 degrees and the wrist and elbow in a straight line (see figure 2). The patient is then asked to ‘press into’ their belly. The test is considered positive if the patient shows weakness in comparison to the opposite shoulder, or if the patient pushes the hand against the abdomen by elbow extension or shoulder extension, indicating an inability to exert force against the abdomen by active internal rotation produced by the subscapularis. This test appears to be specific for demonstrating a subscapularis muscle tendon tear when positive(1).
Figure 2: Belly press sign
Belly off sign (Scheibel et al 2005)(5)
This is a modification to the Napolean test/sign above. The difference here is that the examiner holds the elbow while positioning the hand on the abdomen. The patient is instructed to maintain the position with the wrist straight while the examiner lets go. If the hand lifts off the belly this indicative of a subscapularis tear.
Bear hug test (Barth et al 2006)(6)
In this test, the hand is placed on the opposite shoulder with the elbow anterior to the body (see figure 3). The examiner then applies an external rotation (ER) force while the patient attempts to maintain the hand on the shoulder. The test is positive if the patient is unable to hold the hand on the shoulder as the examiner applies an ER force. If the resistance is 20% less than that of the contralateral side, the test is also considered to be positive. A force equivalent to that of the other side and absence of pain defines the test as negative. The result is considered to be intermediate when the patient is able to resist the examiner’s force but says that it was painful to do so.
Scheifer et al evaluated the test sensitivity and specificity, and when considering the presence or absence of a lesion(7). The sensitivity calculated for the bear hug test was 75%, while it was 25% for the lift-off test. The values for the Napoleon and belly-press tests were respectively 41% and 45%. Using the same criteria, the specificity for diagnosing a lesion (through comparison of the physical examination between patients with a complete tendon and those with a torn tendon) was evaluated. The results obtained were 56% for the bear hug test, 92% for the lift-off test, 80% for Napoleon and 92% for the belly-press test.
Figure 3: Bear hug test
As mentioned above, the sensitivity and specificity of physical examinations are markedly variable, especially if the tear is partial. In particular, clinical evaluation of subscapularis injuries remains difficult for partial upper third (or less) tear. Therefore, the clinician will often rely on diagnostic imaging to determine small and partial lesions to the subscapularis tendon/muscle unit:
Ultrasound – Ultrasound examination is a useful diagnostic tool to detect rotator cuff tears. However, the sensitivity and specificity of ultrasonography in detecting a subscapularis tendon tear is lower than that of supraspinatus and infraspinatus(8). Sensitivity is particularly decreased in the axial view because articular side partial tears are easily masked by external rotation.
MRI – MRI examination is widely accepted as the imaging modality of choice to detect rotator cuff tears. However, just like ultrasonography, the detection rate of subscapularis tendon tear is much lower. In coronal images, the subscapularis tendon and muscle lie in the same anatomic plane, so subtle partial tears or even complete tears are difficult to assess. Therefore, axial-view images are often accepted as the most important in the evaluation of subscapularis tendon.
While it is true that high-contrast axial plane images visualize the anatomic course of the subscapularis tendon, and its insertion on to the lesser tuberosity, specificity for subscapularis tendon abnormalities with sagittal oblique images is higher than those obtained with axial images (although comparable sensitivities may be found)(9).
Walch et al found in a correlation study of MRI and arthroscopic findings, that sagittal oblique images were better at detecting partial one-third tears than axial images(10). However, both axial and sagittal oblique images can only detect upper third tears in 50% of cases. Nonetheless, atrophy and fatty infiltration may be helpful for correct diagnosis by MRI.
Management through strengthening
- Short range internal rotation
The upper subscapularis muscle has been shown to contribute to both shoulder abduction and internal rotation(11). Thus, larger EMG amplitudes from this muscle would be expected during an internal rotation exercise that is performed with progressively greater degrees of abduction (see figure 4 and 5).
Figure 4: Short range internal rotation
To target the upper fibers of the subscapularis, place the arm in a ‘stop sign’ position, with a band around the wrist. Attach the band behind the body at shoulder height (the band around the wrist eliminates the tendency to wrist flex to create the movement). Instruct the athlete to palpate the pectoralis major and the latissimus dorsi with the free hand to ensure that contraction in these muscles is minimized. Internally rotate the shoulder only a few degrees (the hand essentially only moves 1-2 inches). This can be performed as a rapid oscillating movement. Perform in multiple sets of 10 repetitions.
Figure 5: Short range internal rotation forward position
Alternatively, place the arm in a forward flexed position with the elbow in front of the shoulder (figure 4). 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 above.
- Belly-press exercises
This is a similar exercise as described in the belly-press test (see figure 6).
Figure 6: Belly-press exercise
Palpate the pectoralis major and latissimus dorsi with the opposite hand. Place the band around the wrist, not held in the hand. Perform small range internal rotation movements by pressing the hand toward the belly (10 reps x 10 sets).
- Iso-integration of subscapularis into pushing movements.
These exercises are designed to integrate 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 (see figures 7a-7c). The subscapularis (internal rotator) will need to contract to prevent the external rotation from occurring.
The athlete then performs the usual pressing movement of a shoulder/bench press whilst holding the cable/tubing. Perform the standard 3 sets of 10 repetitions whilst holding the band/cable. It is important that the degree of pull from the band/cable is only minimal. With too great a load on the cable or too much tension on the band, an excessive external rotation torque is created that may recruit the more powerful pec major/latisimus dorsi to control the external rotation torque.
Figure 6a: Iso-integration using a dumbbell shoulder press
Figure 6b: Iso-integration using a dumbbell bench press (start position)
Figure 6c: Iso-integration using a dumbbell bench press (finish position)
Surgical –large partial thickness tears of the tendon and full-thickness tears of the tendon are usually surgical candidates similar to large lesions in the other rotator cuff muscles. If conservative measures fail to appropriately return function, refer the athlete for a surgical evaluation.
Research demonstrates that the subscapularis muscle plays an important role in providing anterior glenohumeral joint stability. It centres the humeral head into the glenoid during functional movements of the arm/shoulder. Dysfunction in this muscle may lead to excessive shearing/gliding of the humeral head that may be a precursor to the more serious shoulder impingements and shoulder instabilities. It is important for the clinician to detect dysfunction in this muscle through a battery of tests and direct strengthening exercises will be required to fully rehabilitate function on this muscle.
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