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Despite being the largest and most powerful rotator cuff tendon, the subscapularis has previously been called the “forgotten rotator cuff tendon” because of limited attention historically.1 With improvements in imaging, surgical technology, and techniques, the diagnosis of subscapularis tears has improved. During arthroscopic examination, the incidence of subscapularis tears has been reported to be 30% to 59% in patients undergoing superior rotator cuff repair.2,3 As the ability to diagnose subscapularis tears and understand their role in shoulder function has improved, so too has the treatment of subscapularis tears.
Anatomy
The subscapularis muscle is multipennate and originates from the anterior scapula. It is innervated by the upper and lower subscapular nerves, which are branches of the posterior cord. The subscapularis inserts onto the lesser tuberosity with the upper two-third attachment tendinous and the lower one-third attachment muscular. Richards et al4 described the footprint of the tendinous portion because it inserts onto the lesser tuberosity. The footprint is trapezoidal in shape, with the lateral length (2.45 cm) longer than the medial (1.48 cm) attachment. The upper 60% of the tendon insertion is maintained before it narrows distally.
The upper subscapularis is innervated by the upper subscapular nerve, and the lower portion of the muscle is innervated by the lower subscapular nerve. Multiple studies have demonstrated notable variability in the origin of these nerves, particularly in the lower subscapular nerve, which has been reported to branch off the axillary nerve in up to 55% of cases. Both nerves innervate the subscapularis near the musculotendinous junction, ranging from 15 to 53 mm medial to the junction depending on the position of the arm.5 Yung et al6 recommended that dissection immediately posterior to the conjoint tendon is safe, but additional dissection medial to the conjoint can put the subscapular nerves at risk.
The biceps tendon and sheath are intricately related with the subscapularis tendon. In the lateral rotator interval, deep fibers of the subscapularis connect with anterior supraspinatus fibers. Deep to that, the superior glenohumeral ligament and coracohumeral ligament insert onto the lesser tuberosity. These structures form a sling that stabilizes the long head of the biceps proximally and medially in the bicipital groove. As a result, with tearing of the subscapularis tendon, medial subluxation of the long head of the biceps tendon is often visualized7 (Figure 1).
Figure 1: Axial MRI (proton-density fat saturation) demonstrating full-thickness subscapularis tear and medial retraction (arrow). The long head of the biceps tendon is dislocated medially (asterisk). (Image courtesy of the primary author.)
Diagnosis
Diagnosis of subscapularis tears originates with a detailed history and physical examination. Patients may report a history of recent trauma and/or chronic overuse and can complain of anterior shoulder pain. Patients often have weakness with internal rotation and, in complete tears, increased passive external rotation with their arm at 0 degrees of abduction. Multiple physical examination tests have been described that aid in testing the integrity of the tendon and strength of the muscle.
The belly-press maneuver calls for the patient to press into their belly after the arm is internally rotated, with the elbow anterior to the abdomen. The examination is abnormal if the patient is unable to maintain the elbow in the position, with a test sensitivity of 40% and a specificity of 98%.2 The lift-off test has the patient internally rotate their arm and place the dorsum of the hand behind their back with the elbow flexed at 90°. The patient is instructed to lift the hand off their back, and the examination is positive if the patient is unable to do so. The patient is to keep their elbow flexed at 90°, and one should be aware of patients extending their elbow, giving a false-negative result. The sensitivity of the lift-off test has been reported to be 18%, with a specificity of 100%.2 The bear-hug maneuver originates by positioning the patient's hand on the contralateral shoulder. The patient pushes down into the shoulder, and the examiner tries to counter this and pull the patient's hand off the shoulder. If there is weakness or inability to keep the hand on the shoulder, the examination maneuver is positive (Video 1). Barth et al2 reported the bear-hug test to have a sensitivity of 60% with a specificity of 92%. The belly-off sign is positive when a patient is unable to maintain the palm of the hand attached to the abdomen when the arm is brought into a flexed and internally rotated position. This test is very accurate, with a sensitivity of 86% and a specificity of 91%.8 The internal rotation lag sign originates by asking the patient to place their hand on their back at the level of the lumbar spine. The hand is passively lifted away from the patient's back to near full internal rotation. The test is positive when the patient is unable to hold that position, with the hand dropping back toward the lumbar spine. The sensitivity and specificity of this test are 71% and 60%, respectively.8 The bear-hug and belly press tests are more likely to be positive when the subscapularis tear involves the upper one-third of the tendon, while the lift-off test requires 75% of the tendon to be torn to be positive.2
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Imaging
Imaging studies play an integral role in identifying subscapularis tears in addition to concomitant shoulder pathology. Plain radiographs are often normal with subscapularis tears; however, anterior head subluxation may be found with full-thickness tears. In the setting of chronic massive cuff tear, the humeral head can migrate proximally because of the loss of stabilizing force of the subscapularis and may be associated with cuff tear arthropathy.
Ultrasonography is a tool that allows for in-office, real-time, direct evaluation of dynamic motion controlled by the practitioner. Ultrasonography is useful in patients who have previously undergone shoulder arthroplasty because the metal creates less distorting artifact than on MRI.
CT can diagnose both bony and soft-tissue pathology. Normal musculature will appear hyperdense compared with fat. CT arthrography has shown similar sensitivity and specificity to MRI in detecting rotator cuff tears.9 Fluid extravasation outside of the glenohumeral joint signifies a full-thickness tear, with anterior extravasation onto the lesser tuberosity indicative of a subscapularis rupture. This can also be very helpful in assessing the rotator cuff in patients who have already undergone shoulder arthroplasty or have metallic implants that may distort MRI imaging.
MRI remains the most commonly used imaging technique for evaluating rotator cuff tendons, muscle quality, and bulk. However, multiple studies have demonstrated that subscapularis tears, particularly small tears, can be missed over 60% of the time on MRI compared with arthroscopic examination.10 Adams et al described a technique to more accurately diagnose subscapularis tears on preoperative MRI. When focusing on tendon continuity on axial and sagittal sequences, upper border muscle atrophy, and biceps subluxation, accuracy improved to 86%.11 Although atrophy of the cuff musculature has classically been examined on sagittal images, we also recommend close examination of axial cuts to evaluate the atrophy of the subscapularis because sagittal cuts can, at times, be inadequate to assess muscle atrophy of a retracted subscapularis tear.
Classification
Pfirmann et al first presented a classification of subscapularis tears in 1999. Grade 1 tears are partial tears of the upper subscapularis, grade 2 tears are full-thickness tears of the upper two-third tendon, and grade 3 tears are complete tendon tears.12 Lafosse et al3 later described a modified classification system, highlighting the observation that subscapularis tears seem to extend from deep to superficial and also to delineate reparable tears (types I-IV) from irreparable ones (type V). A type I tear is considered an undersurface partial tear of the upper third. A type II tear is a full-thickness upper third tendon tear. Type III tears are full-thickness tears involving the upper two-thirds with the bottom third still attached. Type IV tears are full-thickness tears involving the entire tendon without humeral head subluxation and Goutallier fatty infiltration equal to or less than grade III. Type V tears are full-thickness tears with humeral head subluxation or fatty infiltration >III.
Indications
As the only anterior rotator cuff tendon, the subscapularis plays an important role in shoulder stability. Contraction of the muscle causes tension anteriorly and a resultant buttressing effect. Loss of this important force can result in anterior subluxation and instability. Collin et al13 showed that in chronic massive rotator cuff tears with fatty infiltration, patients with a combination of complete subscapularis and supraspinatus tears had elevated rates of pseudoparalysis compared with posterosuperior tears. Other studies have examined the outcomes of rotator cuff repair in large multitendon tears, classifying patients into the degree of subscapularis involvement. Tears that, in addition to posterosuperior tearing, exhibited full-thickness subscapularis preoperatively had lower rates of postoperative healing14 and functional outcome.15 Because of the integral role the subscapularis plays in the shoulder and diminished results of delayed repair,16–18 strong consideration should be given to repairing any full-thickness subscapularis tear, particularly an acute tear after traumatic injury in a young, active patient.
Open Repair
The benchmark for the treatment of subscapularis tears has long been considered open repair through a deltopectoral approach. After dissection between the deltoid and clavicular head of the pectoralis muscle, the long head of the biceps tendon can be identified and a tenodesis or tenotomy can be done. The subscapularis tendon can be visualized because it travels inferior to the coracoid toward its attachment onto the lesser tuberosity.
In full-thickness retracted tears, release of adhesions of the tendon may be required deep, superior and anterior to the tendon. In the opinion of the authors, the axillary nerve is more easily identified and protected with an open approach compared with arthroscopic repair techniques, during which the nerve is not routinely visualized.19 Once excursion of the tendon allows for tension-free repair, the lesser tuberosity is débrided to bleeding bone and suture anchors are typically used to repair the tendon. A single-row or double-row repair construct can be used based on surgeon preference, using suture anchors or transosseous sutures. At this time, there is no consensus on whether single-row or double-row constructs are advantageous clinically.18
Gerber and Krushell are largely credited with bringing attention to the importance of identifying and repairing subscapularis tears. In 1991, they reported their technique to repair isolated subscapularis tendon tears in 16 patients and later reported intermediate-term results.16,20 Eighty-one percent of the patients had a good or excellent result and an average of 95% return of function. No notable complications were reported. Edwards et al21 showed improved Constant scores from 55.0 to 79.5 in 84 shoulders using an open technique. Constant scores improved from 55 to 79.5, and 89% of the patients were satisfied or very satisfied with the result. Concomitant biceps tenotomy or tenodesis resulted in improved Constant score, pain score, and subjective result of the repair independent of the preoperative condition of the long head of the biceps tendon. This may be due to a Stener lesion-type effect of the long head of the biceps on subscapularis repairs. As a result, some authors recommend routine biceps tenotomy or tenodesis whenever subscapularis repair is done,17,18 but others have performed a recentering of the biceps and pulley reconstruction with equivalent clinical and objective results when compared with biceps tenotomy/tenodesis.22,23
Arthroscopic Repair
Although subscapularis repairs were historically done through an open anterior approach, with advancements in surgical techniques and implants, arthroscopic repair of the tendon has increased in prevalence. Arthroscopic subscapularis repair can be done in either beach-chair or lateral decubitus position. After a standard posterior portal at the soft spot, typically 2 cm distal and 1 cm medial to the posterolateral corner of the acromion is established, a 30° arthroscope is inserted and an anterior portal is established using an outside in-technique. This portal should ensure direct access to the subscapularis footprint on the lesser tuberosity for anchor placement. A third anterolateral accessory portal can be used, particularly in large tears, through the rotator interval for isolated subscapularis tears or to be used later as a working portal for supraspinatus/infraspinatus repair when present (Figure 2). Proper placement of portals is important to allow direct access to the subscapularis and lesser tuberosity, prevent interference between instruments or cannulas, and facilitate repair.
Figure 2: A, Illustration showing portals used for subscapularis repair. A—Anterior portal, B—anterolateral portal through rotator interval or supraspinatus tear, when present, and C—posterior viewing portal. B, Right shoulder in the beach-chair position, with landmarks demarcated. A—Anterior portal, B—anterolateral portal, and C—posterior viewing portal. (Both reproduced with permission from Kuntz AF, Raphael I, Dougherty MP, Abboud JA: Arthroscopic subscapularis repair. J Am Acad Orthop Surg 2014;22[2]:80-89.)
Identification of subscapularis tears can be challenging, and visualization of the tendon and lesser tuberosity is paramount. With the arm flexed and internally rotated, posterior humeral translation can help identify the size and extent of the tear. Tears of the subscapularis can be visualized from the posterior portal or anterolateral portal from the subacromial space. Particularly when viewing from posteriorly, a 70° arthroscope can aid in visualization of lesser tuberosity, tear extent, and/or a retracted subscapularis tear medial to the glenoid face. An arthroscopic grasper can be used to grasp the tendon at the insertion to assess the integrity of the insertion (Video 1).
The extent of mobilization needed for the tendon during repair is determined by the size of the tear and the chronicity of the injury. Partial thickness or upper border full-thickness tears have limited retraction because of continuity of the remaining tendon. In larger tears, retraction may extend medial to the glenoid surface. In this case, the “comma” tissue, comprising the medial sling of the biceps sheath, the avulsed coracohumeral ligament, and the superior glenohumeral ligament, retracts with the subscapularis tendon and is a landmark to find the superior lateral edge of the retracted tendon. With an intact subscapularis tendon, the comma tissue lies in an oblique orientation extending from inferolateral to superomedial. In the setting of a torn and retracted subscapularis tendon, the comma tissue can be vertical or from inferomedial to superolateral in orientation. Recognizing the comma tissue can be helpful in assessing position for the repair of the tendon (Video 1). As in open repair, traction sutures can provide tension for arthroscopic releases. Adhesions of the subscapularis can prevent adequate mobilization of the tendon. The undersurface of the coracoid can be exposed through the rotator interval, and the subscapularis can be released of adhesions superiorly toward the coracoid, posteriorly and anteriorly.
Once the tendon is adequately mobilized, repair can be done similar to open techniques. Our preferred technique is to use suture anchors to repair the tendon from a caudal to cranial direction. Multiple repair constructs have been described, including knot-tying versus knotless methods and single-row and double-row constructs, which can be done according to surgeon preference. In large retracted tears, Denard and Burkhart24 showed that the subscapularis tendon can be repaired up to 7 mm medial to the lesser tuberosity if necessary to prevent excess tension on the repair without compromising results.
Burkhart was the first to report clinical results of all arthroscopic-isolated subscapularis repairs in 2002. In their initial series of 25 patients, average forward elevation improved from 96 to 146 and University of California at Los Angeles scores improved from 10.7 to 30.5.1 With a long-term follow-up, 80% of the patients were classified as having a good or excellent result, and 83% of the patients returning to their usual activity level.25 Similar excellent results of arthroscopic subscapularis repair have been reported by others, showing consistent improvement in shoulder function scores, low complication rates, and association between strength recovery and tendon healing in multiple studies.3,26,27
On reviewing the recent literature, a trend toward improved shoulder function scores and lower retear rates in double-row compared with single-row repairs has been seen.18 However, owing to the paucity of data, no consensus can be reached at this time, and additional research focusing on subscapularis repair techniques is needed. Similarly, the data comparing open to arthroscopic subscapularis repairs are limited. Two studies have retrospectively compared the results of arthroscopic subscapularis to open repair, with both techniques demonstrating similar results.28,29 A meta-analysis of nine studies compared results of open to arthroscopic subscapularis repair.30 Both techniques result in pain relief, improved shoulder function, and low complication rates, with possible lower postoperative pain scores in patients undergoing arthroscopic repair.
Tendon Transfers
Chronic or large subscapularis tears with severe tendon retraction, degeneration, and advanced muscle atrophy may not be reparable. In some patients, a tendon transfer may help improve strength and function of the shoulder. Tendon transfer should generally be reserved for physiologically young patients without advanced glenohumeral arthritis who are willing to undergo a meticulous rehabilitation protocol. Although multiple transfers, including the pectoralis minor and trapezius, have been described for irreparable subscapularis tears, the most commonly used transfers are the pectoralis major and latissimus dorsi.
Wirth and Rockwood31 first described pectoralis major transfer in patients with recurrent anterior glenohumeral subluxation/dislocation from irreparable subscapularis tendon. In their technique, the upper two-third tendon of the pectoralis major is transferred to the lesser tuberosity, anterior to the coracobrachialis. Resch et al reported on their modification to the Wirth surgical technique, transferring the pectoralis major deep to the conjoint tendon in an effort to more accurately recreate the line of pull of the subscapularis. In 12 patients, Constant scores improved from 26.9 to 67.1 and pain scores improved 7.9 points out of 15. The overall subjective score improved from 20 to 63 postoperatively.32 Subsequently, this subcoracoid transfer was found to have biomechanical advantage when compared with a supracoracoid transfer and more closely recreates native glenohumeral mechanics.33 To date, we are unaware of studies that have directly compared the clinical results of subcoracoid and supracoracoid pectoralis transfers. Ernstbrunner et al34 published their long-term results of supracoracoid pectoralis transfers. At a mean 20-year follow-up, all 30 patients described their results as good or excellent. However, declining function elevated rates of cuff tear arthropathy and recurrent instability have been reported by others35,36 with a long-term follow-up.
More recently, latissimus dorsi tendon transfer has been investigated as an option for irreparable subscapularis tears. When considering tendon transfers, the ideal transferred tendon has minimal donor site morbidity, similar line of pull, muscle tension/strength, and adequate excursion to best substitute for the irreparable tendon. The latissimus dorsi's native orientation is posterior to the chest wall and more in line with the subscapularis, compared with the pectoralis major that lies anterior to the chest (Figure 3).
Figure 3: Schematic showing right shoulder: single dot demarcates the subscapularis tendon, and two dots are at the latissimus major. Both muscles originate from posterior to the chest wall. (Reproduced with permission from Elhassan B, Christensen TJ, Wagner ER: Feasibility of latissimus and teres major transfer to reconstruct irreparable subscapularis tendon tear: an anatomic study. J Shoulder Elbow Surg 2014;23[4]:492-499.)
The procedure can be done through an open or arthroscopic-assisted approach. When done from a deltopectoral approach, the upper 1 cm of the pectoralis tendon is released. Deep to this, the latissimus dorsi tendon is identified and bluntly dissected from the teres major. The latissimus tendon is then released off its insertion, carefully released of adhesions, and secured with a Krackow locking stitch using a nonabsorbable suture. Excursion to the lesser tuberosity (for subscapularis-only tears), or to the greater tuberosity (for combined supraspinatus and subscapularis irreparable tears), is confirmed, and the latissimus is then secured through an over-the-top repair configuration using suture anchors (Figure 4).
Figure 4: Photograph demonstrating completed latissimus major tendon transfer. A running, locking nonabsorbable suture has been passed through the tendon and secured onto the lesser tuberosity using two knotless suture anchors (asterisks). (Reproduced with permission from Mun SW, Kim JY, Yi SH, Baek CH: Latissimus dorsi transfer for irreparable subscapularis tendon tears. J Shoulder Elbow Surg 2018;27[6]:1057-1064.)
The technique was first described by Elhassan et al37 who recently reported on outcomes on 56 patients using an arthroscopic-assisted technique. Notable improvements in pain, flexion, abduction, internal rotation, and Constant scores were noted. Two other reports have demonstrated similarly encouraging results with minimal complication rates and no neurologic deficits.38,39 However, it should be noted that approximately 25% of the patients demonstrate proximal migration on radiographs,37 and additional research is needed to determine the long-term results of latissimus transfer. In addition, no studies have compared clinical outcomes between pectoralis transfers and latissimus transfers for irreparable subscapularis tears.
Anterior Capsular Reconstruction
The absence of a functional subscapularis can result in anterior instability of the glenohumeral joint due to loss of the force couple. Surgeons have attempted to provide a static anterior restraint by reconstructing the anterior capsule of the glenohumeral joint with autograft or allograft tendon grafts. However, the results were historically unpredictable with up to 55% of patients demonstrating residual instability.40 With the recent encouraging results of superior capsular reconstruction for irreparable posterosuperior tears, multiple authors have published their technique for anterior capsular reconstruction (ACR) using a decellularized dermal allograft as a treatment option for irreparable subscapularis tears41,42 (Figure 5). Through arthroscopic techniques or an open approach, the lesser tuberosity and anterior glenoid neck are decorticated to punctate the bleeding bone. Suture anchors are applied to the anterior glenoid and lesser tuberosity, and the dermal allograft is sized to match the defect. The graft is first fixed medially to the glenoid and then to the humerus while ensuring adequate tension to the graft. Margin convergence sutures can be applied to the lateral supraspinatus or residual subscapularis when possible. Two recent biomechanical studies demonstrated that ACR imparts enhanced anterior-inferior stability than pectoralis major or latissimus tendon transfers in cadaver models.43,44 However, to the best of our knowledge, there are no clinical studies showing results of the dermal allograft ACR for irreparable subscapularis tears.
Figure 5: Photograph demonstrating anterior capsule reconstruction using an acellular dermal allograft. Arrows indicate a knotless transosseous equivalent fixation of the graft onto the lesser tuberosity (marked with asterisk). Margin convergence sutures have been placed to the supraspinatus tendon (triangles). (Reproduced with permission from Pogorzelski J, Hussain ZB, Lebus GF, Fritz EM, Millett PJ: Anterior capsule reconstruction for irreparable subscapularis tears. Arth Tech 2017;6[4]:e951-e958.)
Reverse Shoulder Arthroplasty
Unlike the anatomic shoulder, the reverse prosthesis is a semiconstrained prosthesis because of the radius of curvature of the socket matching that of the glenosphere. Although initially designed as a treatment of cuff tear arthropathy, indications for reverse shoulder arthroplasty have expanded to include more than elderly patients with irreparable rotator cuff tears and glenohumeral arthritis. Relative indications for reverse shoulder arthroplasty in the treatment of irreparable rotator cuff tears include static anterior or anterosuperior subluxation and pancircumferential irreparable rotator cuff tears (involvement of subscapularis, supraspinatus, and infraspinatus with or without teres minor extension).45 There also exists controversy in whether joint preserving procedures, such as tendon transfers or capsular reconstructions, can reliably reverse pseudoparalysis.45 Specific to reverse shoulder arthroplasty, surgeons must weigh the possibility of complications, such as instability, dislocation, acromial fractures, and periprosthetic fractures. No clinical studies examining outcomes of reverse shoulder arthroplasty for isolated subscapularis tears have been reported.
Summary
With improvements in surgical techniques and technology, our understanding and treatment of subscapularis tears have improved. Although open techniques have been used to repair subscapularis tears with success, the trend has shifted to fix them through an arthroscopic approach. In the case of irreparable subscapularis tears, pectoralis major transfer has demonstrated good results with a long-term follow-up. Latissimus transfer for such tears provides biomechanical advantages and can be safely done, but long-term clinical results are not yet available. The role of anterior capsule reconstruction in the treatment of irreparable tears also remains unclear, and its role in the treatment of irreparable subscapularis tears requires additional research. Reverse shoulder arthroplasty is an option for patients with irreparable cuff tears and subluxation or pseudoparalysis, ideally in elderly patients with lower activity demands.
References
References printed in bold type are those published within the past 5 years.
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