The subscapularis represents the anterior portion of the rotator cuff and is an important stabilizer and internal rotator for the glenohumeral joint. The first case documenting a subscapularis tendon tear was reported by Smith in 1834, and the first reported repair was described by Hauser in 1954. A subscapularis injury can be isolated or found in combination with other rotator cuff tendons, and it may include the long head of the biceps. Failure to identify an injury to this structure can lead to prolonged disability including pain, weakness, and poor function. More recent studies have demonstrated higher rates of subscapularis pathology than expected. Bennett reported a 27% rate of subscapularis pathology in a series of 165 patients with a shoulder treated arthroscopically; subscapularis tearing was involved in 35% of all rotator cuff pathology. Corroborating the findings of the study by Bennett, Arai and colleagues reported an overall subscapularis tendon tear involvement of 27.4% in 435 consecutive arthroscopies that they reviewed.
Different age groups often present with different injuries to the subscapularis. Adolescent athletes may injure the lesser tuberosity physis (i.e., a Salter II fracture) or avulse the subscapularis insertion while playing sports ( Fig. 53-1 ). Tuberosity displacement along with the attached subscapularis can be a challenge diagnostically and surgically. Middle-aged athletes may sustain a traumatic isolated subscapularis tear or an anterosuperior cuff tear, which can range from articular-sided partial tears with destabilization of the long head of the biceps to a large tear combined with pain and stiffness ( Fig. 53-2 ). Elderly patients may present with a massive tear that is often the result of an acute extension of a prior minimally symptomatic chronic tear, leading to instability and possible anterior escape ( Fig. 53-3 ). Many patients have found a way to continue to participate in sports with a small supraspinatus tear; however, when tears extend into the subscapularis and infraspinatus, the stabilization effect of the cuff can be compromised and can create significant problems. During open surgical repair, tear extension can be undetected, leading to persistent symptoms.
The subscapularis muscle is the largest and most powerful of the four rotator cuff muscles. In isolation, it provides approximately 50% of the rotator cuff force. The muscle originates from the anterior surface of the scapula and typically is split up into the upper two thirds and the lower third. The upper two thirds insert on the lesser tuberosity, and the lower third inserts onto the humeral metaphysis. The tendinous portion of the muscle represents the upper third and inserts on the superior aspect of the lesser tuberosity. Hinton et al. studied 25 cadavers and found that the superior 60% of the muscle’s insertion onto the lesser tuberosity was tendon, whereas the remaining insertion consisted of muscle below the lesser tuberosity. These investigators also found that the musculotendinous junction was fully formed approximately 2 cm from the lesser tuberosity. The upper tendinous portion is what can be visualized arthroscopically. In a cadaveric study of six shoulders, Wright et al. demonstrated that the superior 44% of the subscapularis could be visualized arthroscopically. In this study it was also found that the margin of safety between the lower border of the subscapularis and the axillary nerve is 32.8 ± 6.0 mm. The upper portion of the subscapularis tendon interdigitates with the anterior fibers of the supraspinatus tendon to contribute to the rotator interval structure, as well as the transverse humeral ligaments. This interval is important because it provides stability for athletes who participate in sports that involve overhead action. Articular blending of fibers is significant in biceps pulley stability. Extraarticular structures of the interval include the coracoid and coracohumeral ligament.
The upper and lower subscapular nerves provide innervation to the subscapularis muscle. The majority of the muscle is innervated by the upper subscapularis nerve, which originates from the C5-C6 nerve roots off the posterior cord of the brachial plexus. The lower subscapularis nerve innervates the axillary portion of the subscapularis, as well as the teres major. In a common variation of the nerve supply, the axillary nerve can produce one or two small branches and supply innervation to the axillary portion of the subscapularis. The majority of the blood supply to the subscapularis muscle is derived from the subscapular artery. The subscapular artery, the largest branch of the axillary artery, arises at the lower border of the subscapularis, which it follows to the inferior angle of the scapula.
Several cadaveric studies have shown that the superior portion of the footprint on the lesser tuberosity represents the widest portion of the insertion. The insertion is trapezoidal; the widest portion is superior, tapering in width at the distal attachment. Based on these studies, it is believed that the most superior attachment of the subscapularis is the strongest and is the location where tears begin and progress.
The primary function of the subscapularis muscle, along with the pectoralis major, the latissimus dorsi, and the teres major muscles, is to internally rotate the shoulder. Favre et al. described the cranial and middle segments of the subscapularis muscle as internal rotators with the arm in an adducted position. The muscle also acts as a force couple along with the posterior rotator cuff (infraspinatus and teres minor). In concert, these muscles provide a stable fulcrum for glenohumeral joint motion. The subscapularis also opposes the action of the deltoid to allow humeral elevation and abduction by the supraspinatus. Given its anterior location with relation to the glenohumeral joint, the subscapularis contributes to humeral head stability, opposing anterior subluxation/dislocation.
Mechanism of Injury
A bimodal distribution seems to exist with regard to subscapularis injuries. In the traumatic setting, injuries typically are sustained to the subscapularis with the arm in hyperextension and external rotation. Gerber and Krushnell described 16 patients who sustained isolated subscapularis tendon tears with a forced external rotation in an adducted arm. Deutsch et al. evaluated a cohort of 14 shoulders with subscapularis injuries. All but three patients sustained a traumatic injury of hyperextension or external rotation of the abducted arm. The average age of their patient population was 39 years, and all of the patients were male.
An association also exists with regard to anterior glenohumeral dislocation in the older patient population and subscapularis failures. Neviaser and Neviaser described a series of 11 patients with traumatic, recurrent anterior instability of the glenohumeral joint leading to subscapularis insufficiency. The average patient age in their series was 62.7 years, and in all cases, stability was restored with repair of the anterior capsule and subscapularis. In skeletally immature patients, lesser tuberosity avulsion has been described. A missed diagnosis and subsequent missed repair can lead to significant morbidity ( Fig. 53-1 ).
The majority of acute subscapularis tears occur in conjunction with supraspinatus tears, termed “anterosuperior lesions of the rotator cuff.” With more degenerative tears of the subscapularis, coracoid impingement has been implicated. Lo and Burkhart have described the “roller-wringer effect” that can occur when the coracohumeral interval is less than 6 mm. In this phenomenon, the tip of the coracoid impinges upon the subscapularis tendon, creating tensile forces on the articular surface and leading to tensile undersurface fiber failure lesions. Forward elevation, internal rotation, and cross-body adduction may cause impingement of the subscapularis tendon between the tip of the coracoid and lesser tuberosity.
Biceps injuries are often found concomitantly with subscapularis injuries. Several studies have demonstrated medial biceps subluxation or frank tearing as a result of subscapularis insufficiency. Arai et al. reviewed 435 consecutive arthroscopies and found that in all cases in which biceps instability was present, associated subscapularis tearing occurred. In fact, biceps symptoms and pathology often lead to the diagnosis of subscapularis insufficiency. A likely phenomenon for this association is that the superior border of the subscapularis contributes to the pulley mechanism that retains the biceps tendon groove.
Several classification systems for subscapularis tendon tears have been proposed. In general, tears are classified as partial thickness, full thickness with no retraction, and full thickness with retraction. Pfirrmann et al. classified tears according to three grades, with grade I being involvement of less than 25% of the superior to inferior length of the tendon, grade II being more than 25% of the tendon, and grade III being complete full-thickness tears. Based on intraoperative evaluation and preoperative computed tomography (CT) scans, LaFosse et al. classified subscapularis tendon tears into five types. Type I is a partial lesion of the superior one third; type II is a complete lesion of the superior one third; type III is a complete lesion of the superior two thirds; type IV is a complete tendon lesion with a centered head and fatty degeneration less than or equal to stage 3; and type V is a complete lesion with an eccentric head and coracoid impingement, as well as fatty degeneration greater than stage 3.
History and Physical Examination
The clinical presentation for ruptures of the subscapularis can be extremely varied, especially if the injury is an acute and traumatic injury versus a degenerative process. Younger patients with an acute traumatic injury typically have acute-onset shoulder pain with limited motion. Even if they did not sustain a frank dislocation, their symptoms may mimic those of a dislocation. Pain may also be related to concomitant biceps pathology. Patients with degenerative subscapularis tendon tears typically present with symptoms like those of persons with degenerative superior and posterior rotator cuff tears. They have gradual, progressing symptoms, usually in the anterior shoulder region. Once again, biceps pain is quite common in this setting.
During the physical examination, it is important to be able to visualize and inspect both shoulders to compare them for symmetry. Tenderness in the anterior shoulder region over the bicipital groove and lesser tuberosity is common. If pain is limited, patients can demonstrate exaggerated passive external rotation compared with the contralateral side. Weakness in internal rotation is common, but in chronic tears, patients often use the other internal rotators (i.e., the latissimus, pectoralis major, and teres major) to compensate for their lack of subscapularis, which can cloud this physical examination finding.
Three accepted specialty tests that isolate the subscapularis muscle have been described ( Fig. 53-4 ). The lift-off test and belly-press test have been described by Gerber and colleagues, and the more recently described bear-hug test has been demonstrated by Barth and colleagues to accurately diagnose subscapularis tears. A prerequisite for the lift-off test is for the patient to have minimal pain with motion and to be able to internally rotate the shoulder without pain. In this test, the patient internally rotates his or her hand behind the back and initially rests the dorsum of the hand on the midlumbar region. A positive test occurs when the patient is unable to lift or maintain the hand away from the back. Clinicians have made comparisons regarding the accuracy and validity of these examination techniques.
Compared with the lift-off test, the belly-press test is easier to perform for a patient with more limited, painful motion. In this test, the patient places the palms of both hands around the level of the umbilicus with the wrists in a neutral position. A positive test occurs when the patient is forced to volar flex the wrist in an attempt to maintain a forward position of the elbow, while the elbow actually falls posteriorly. A decrease in the ability to maintain a forward position of the elbow compared with the contralateral side also indicates subscapularis insufficiency.
The bear-hug test involves placing the palm of the hand of the side that is being tested upon the opposite shoulder with the fingers extended. The patient then attempts to resist an external force by trying to pull the hand away from the shoulder in a perpendicular fashion. A positive test occurs when the patient is unable to maintain the hand on the opposite shoulder or shows weakness compared with the contralateral side.
Electromyographic testing has demonstrated that the subscapularis muscle activity is proportionally greater than the other internal rotators of the arm in the lift-off test with the hand at the midlumbar level. In addition, Tokish et al. used electromyographic validation and comparison to demonstrate that the belly-press test preferentially activates the upper subscapularis, whereas the lift-off test preferentially activates the lower subscapularis muscle. In another electromyographic study, arm position while performing the bear-hug, belly-press, and lift-off tests was evaluated. It was concluded that all three tests were successful in significantly isolating subscapularis function and that no difference in activation was found at different arm angles.
The initial diagnostic workup includes radiographs of the shoulder, including an anteroposterior view in external rotation, a transscapular outlet view, and an axillary lateral view. Preservation of the glenohumeral joint, the acromiohumeral interval, and anatomy of adjacent structures, including the acromion and acromioclavicular joint, can be determined. In persons with acute subscapularis ruptures, a small segment of the lesser tuberosity is sometimes avulsed and can be appreciated on radiographs.
Additional studies to evaluate the soft tissue are also necessary, including magnetic resonance imaging (MRI), CT with use of contrast material, or ultrasound. Ultrasound has the added benefit of a dynamic imaging study, although it is operator dependent. These studies can help evaluate tear retraction, but MRI and CT studies are better indicators for muscular atrophy and fatty infiltration. The presence of muscle atrophy and extensive fatty infiltration has been correlated with poor healing after repair. MRI provides the added benefit of evaluating common concomitant pathology such as labral tears and biceps injuries ( Fig. 53-5 ).
The accuracy of MRI imaging in the detection of subscapularis lesions has been called into question in the literature. Adams et al. retrospectively reviewed 120 patients who underwent arthroscopic rotator cuff repair and correlated arthroscopic findings with MRI findings with respect to subscapularis tears. All 16 patients with a subscapularis tear that was identified on preoperative MRI imaging had confirmed tears at arthroscopy, for a specificity of 100%. However, only these 16 tears were identified on MRI imaging, whereas a total of 44 tears were found at the time of arthroscopy, yielding a sensitivity of only 36%. A more recent study performed by Foad and Wijdicks confirmed the aforementioned findings, even when MRI arthrography was implemented. In their study, subscapularis tears were identified in 40 shoulders at the time of arthroscopy, whereas a lesion was identified in only 15 of these shoulders in a preoperative MRI study. Interestingly, the sensitivity of noncontrast MRI versus MRI arthrography was 40% versus 36%, indicating that the accuracy of identifying subscapularis tears does not dramatically differ even when arthrography is used.
The dynamic nature of ultrasound is one major advantage over traditional MRI. Farin and Jaroma used ultrasound to evaluate 17 patients with confirmed subscapularis tears at the time of arthroscopy. In their study, 14 of 17 tears (82%) were accurately determined preoperatively with use of ultrasound.
Different surgical approaches have been recommended for different presentations when determining surgical repair. When considering an arthroscopic repair, posterior tear extension in multiple tendon tears and destabilization of the pulleys of the biceps should be appreciated when planning the steps of surgical repair. Surgical access to the subscapularis is limited, and swelling can make it difficult to access. Initial repair of the subscapularis can avoid problems with access and can be followed with repair of the adjacent structures.
Open and arthroscopic approaches have been described for repairing cuff tears that include the subscapularis. Arthrotomy and repair of an isolated subscapularis tear can be performed with a deltopectoral approach. Tears may extend posteriorly through the supraspinatus and potentially the infraspinatus, and this scenario may require an additional deltoid split to avoid extensive traction on the deltoid. Arthroscopic expansion with saline solution may dissect along the chest wall and base of the neck. Anesthesiologists should be informed about this procedure preoperatively, because it may affect their decision regarding intubation and patient positioning.
The timing of surgical repair and delay in treatment can be detrimental to outcome. The anterosuperior cuff tear is often the result of a traumatic event. Based on personal experience, some patients have shoulder stiffness at the time of presentation, perhaps because of the rotator interval and biceps proximity. Initiating range of motion preoperatively, followed by planned repair, is recommended to optimize the recovery from this injury.
Tendon mobilization is performed through a series of releases from the articular and bursal surfaces. The articular releases include portions of the middle glenohumeral ligament. The bursal releases can be performed along the lateral border of the coracoid, with the addition of a decompressive coracoplasty. Thickened capsule structures along the superior border of the subscapularis comprise the medial pulley to the biceps and the coracohumeral ligament. Preservation of these structures will assist in reduction of the leading edge of the supraspinatus tendon. Interval releases medial to these structures can be performed and assist in visualization of the superior portion of the subscapularis repair.
Surgeons have two different philosophies regarding arthroscopic repair of the subscapularis involving the portal used to visualize the repair. Some surgeons choose to visualize the repair from the posterior articular portal. The superior border tears, either partial or complete, are easily accessed through working portals in the rotator interval. A bursal view may be used for significantly retracted tears that require additional bursal releases. Surgeons who prefer this view from either a lateral or anterosuperior portal can mobilize tears that have retracted. It is prudent to understand use of both viewing portals to maximize the approach for the more complex retracted tears.
Several approaches can be taken after a subscapularis injury, ranging from a nonoperative approach to surgical repair. Because of the importance of shoulder internal rotation strength and the potential for the development of chronic anterior instability, repair is often recommended after an acute event.
Nonoperative management can have variable results. Few anecdotes have suggested benign neglect in patients who are otherwise debilitated or have multiple morbidities. Certain patients may have a thin or deficient subscapularis after prior surgical arthrotomies, z-plasties, or releases. Fortunately, other muscles extending from the thorax can assist with internal humeral rotation. A concern is the possible development of anterior instability, which can present at varying degrees of severity, ranging from episodic subluxation to a fixed anterior deformity ( Fig. 53-3 ). These problems are complex with regard to attempted reconstruction, and therefore earlier management of the subscapularis tear is recommended in most patients after this structure is injured.
An open approach traditionally has been taken to the surgical repair of a torn subscapularis. Muscle detachment is not necessary with a deltopectoral anterior approach. From a bursal perspective, the biceps and brachialis attachment to the coracoid can be protected, and the shoulder can be positioned with moderate external rotation to more easily create exposure of the lesser tuberosity. Finger palpation of the musculocutaneous nerve and axillary nerve permits mobilization of the subscapularis tendon in patients with retraction after a tear. In most cases, a variety of techniques are used to perform tenodesis with the biceps during the open repair. Disadvantages of an open repair include potential difficulty in managing portions of the rotator cuff tear that extend posteriorly and superiorly. By internally rotating the humerus and extending the arm, a limited view of the anterior portion of the supraspinatus can be illustrated. This posture often provides tension to this structure, and thus mobilizing it to the greater tuberosity is a challenge. In cases in which surgeons choose an open approach, the addition of a deltoid split or a split posterior to the junction of the anterior and middle thirds of the deltoid would make the exposure of the greater tuberosity easier to obtain, with less deltoid retraction.
Arthroscopic approaches to repairing subscapularis and rotator cuff tears continue to increase in popularity. The advantages of the arthroscopic approaches include complete articular examination, visualization of articular and bursal releases, avoidance of detachment or mobilization of the deltoid, the potential management of articular and bursal coexistent pathologies, and the reduction of certain complications (e.g., infection due to the nature of arthroscopic irrigation).
Arthroscopic techniques to repair the subscapularis can be performed with either articular or bursal viewing portals. Proficiency with both techniques provides the surgeon with multiple options for repairing large retracted tears ( Fig. 53-6 ).