Subscapularis tendon tear

Subscapularis tendon tears are a less common rotator cuff tear, and have been considered more difficult to diagnose pre-operatively (both clinically and radiological) and have been known as a "hidden lesion" ⁵. Accurate pre-operative diagnosis is important as it affects the surgical approach and delayed/missed treatment can result in poor functional outcomes compared to earlier diagnosis ⁴.

Epidemiology

Subscapularis tears account for ~4% (range 2-6%) of rotator cuff tears ³.  The clinical prevalence of subscapularis tendon tears has been estimated at ~15% (range 5-30%) although is higher in patients undergoing rotator cuff surgery at ~55% (range 49-62%) and in cadaveric studies ~33% (range 29-37%) ^1,4,9. 

Clinical presentation

Many patients are asymptomatic. Symptomatic subscapularis tendon tears present with anterior shoulder pain and instability ^1,3. Clinical examination maneuvers include the lift-off test, belly-press test, and the bear hug test ⁵.

Pathology

Three patterns of subscapularis tendon tears have been described ^1-3:

• supraspinatus tendon involvement or as part of a massive rotator cuff tear

  • 80% of subscapularis tears also have a supraspinatus tendon tear

• rotator interval extension potentially involving the superior glenohumeral ligament (SGHL) and coracohumeral ligament (CHL) and can lead to biceps instability, especially when superior tears are present

• isolated: rare; most commonly traumatic in the setting of anterior glenohumeral instability

Subscapularis tears almost always (>90%) start as articular-sided partial-thickness tears superomedially and progress inferolaterally ^1,4,5,7. The entire tendon can be torn but the overlying superficial fascia and transverse humeral ligament can be intact. Less commonly, bursal-sided partial-thickness tears and/or interstitial delamination ¹.

Associations

Besides the above structures implicated in patterns of subscapularis tendon tears, there are associations with:

• subcoracoid impingement ³

• SLAP tears in the context of biceps pulley injury ³

Classification

Numerous classification systems exist (in no particular order) ^4,5,9:

• Fox and Romeo classification

• Lafosse classification (arthroscopic)

• Pfirrmann classification (MR arthrography)

• Yoo and Rhee classification (conventional MRI)

Radiographic features

Imaging has a low sensitivity (~40%) on ultrasound and variable sensitivity (35-87.5%) on MRI for the detection of subscapularis tears ^4,5,8,9. Imaging findings for subscapularis tendon pathology are similar to those elsewhere with a few specific features that may aid in diagnosis. 

Ultrasound

Long head of biceps tendon sheath effusion >2 mm has been associated with subscapularis tendon tears ⁵. 

MRI

Subscapularis tears can have intermediate or fluid-like intrasubstance tendon signal, tendon margin irregularity, tendon defect and/or tendon retraction ⁸. Findings helpful for the diagnosis of subscapularis tendon tears:

• increased sensitivity (~75%) of subscapularis tears has been demonstrated when two of the following four findings are present ⁷

  • axial plane: subscapularis tendon tear from the lesser tuberosity

  • axial plane: long head of biceps (LHB) tendon subluxation

  • sagittal oblique plane: subscapularis muscle belly atrophy

  • sagittal oblique plane: bare lesser tuberosity with torn subscapularis fibers

• lesser tuberosity bone marrow edema and cysts especially when combined with muscle belly fatty atrophy is indicative of chronic tears ^2,3

• comma sign: full-thickness superior subscapularis tears along with SGHL and CHL tears retracted superiorly

• if the LHB is normally positioned in the bicipital groove (i.e. not subluxed), there is a low likelihood of a full-thickness subscapularis tear ⁶

Treatment and prognosis

The principles of subscapularis tendon repair are similar to general principles for rotator cuff tears. Surgical repair can be performed open or arthroscopically without or without augmentation. Salvage operations for complete, chronic tears include anterior capsule construction, tendon transfers (pectoralis major, pectoralis minor, latissimus dorsi), or reverse shoulder arthroplasty if there is glenohumeral osteoarthritis ⁵.