Subscapularis Tendon

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Pseudoparalysis is defined as an inability to actively elevate the arm beyond 90 degrees with full passive forward flexion. Prevalence of subscapularis lesion is high (around 50% of arthroscopic rotator cuff procedures, 10% are isolated). The superior two-thirds of the subscapularis ends as a tendon that inserts on the lesser tuberosity of the humerus. The inferior part has no tendon; the muscle attaches directly to the bone. The subscapularis should be considered as two different muscles. It is the largest and most powerful of the rotator cuff muscles. The subscapularis is an internal rotator and is crucial for shoulder elevation. Several special tests have been described to aid in diagnosis, including the lift-off, belly-press, and bear-hug tests. Mulitple magnetic resonance imaging (MRI) views should be analyzed to increas the chance of subscapularis lesion detection. FUSSI and SAM are similar conditions causing abrasion of the upper and medial part of the subscapularis tendon. 90% of patients with a subscapularis tear have associated long head of the biceps lesions or instability. Preservation of the intra-articular biceps will frequently jeopardize the repair. Results are good or excellent in around 80% of cases. Around 90% of patients returned to normal activities, and 90% are satisfied.

Key words

Subscapularis tendon; Rotator cuff lesion; Biomechanics; Classification; FUSSI; SAM; Lafosse; Toussain; Results; Complications; Irreparable; Anatomy; Pectoralis major transfer; Imaging; Pseudoparalysis.

Definition of Pseudoparalytic Shoulder

Pseudoparalysis is defined as an inability to actively elevate the arm beyond 90 degrees with full passive forward flexion. It is also important to note that this is functional limitation and not pain inhibition; this can be distinguished by the inability to hold the arm at 90 degrees and/or an evaluation of motion after a subacromial injection. Anatomically, pseudoparalysis requires the disruption of at least one rotator cable attachment. Recently it has been demonstrated that dysfunction of the entire subscapularis and supraspinatus or three rotator cuff muscles are risk factors for pseudoparalysis.[1]

Primary arthroscopic repair can lead to reversal of pre-operative pseudoparalysis in 90% of patients, but in only 43% of revision surgeries.[2]

Anecdote

Like teres minor, the subscapularis has been a “forgotten tendon” of the rotator cuff.[3]

In the 1980s, at a meeting of the American Academy of Orthopaedic Surgeons in Orlando, Christian Gerber presented a new, unknown clinical entity, the “Isolated tear of the subscapularis tendon“. The presentation was based on 16 cases with computed tomography (CT)-arthrography or magnetic resonance imaging (IRM), intraoperative photographs of all cases and included a detailed description of the clinical features including lift- off test, belly-press test and increased passive external rotation. The discusser of the paper felt that this was a nice presentation which unfortunately lacked a bit of relevance as this entity was not observed in the US and was probably a "Swiss disease“. Certainly, he and his experienced expert colleagues had never seen it. Dr Richard Hawkins, who had visited Christian Gerber a few weeks earlier and participated in two isolated subscapularis tendon repairs got up in the audience and told the discusser. "I don’t doubt that you, as I, have never seen an isolated subscapularis tear, but after my visit I can tell you that many have seen us".

Christian Gerber submitted the paper to the American Journal of Bone and Joint Surgery which rejected it, because the reviewers could not see the relevance for the English speaking readership. It was published in the British Journal of Bone and Joint Surgery in 1991.

Isolated subscapularis tears are currently known to represent about 8-10% of all the rotator cuff tendon tears as well in Europe as in America.

Prevalence

Because articular sided tears are not commonly visualized during open approaches, subscapularis tears were previously believed to be rare. They are now recognized to have a prevalence of nearly 30% in all arthroscopic shoulder surgery, and up to 59% in arthroscopic rotator cuff procedures. Isolated subscapularis tears are currently known to represent about 8-10% of all the rotator cuff tendon tears.[4][5][6][7]

Anatomy of the Subscapularis

The subscapularis muscle arises from the anterior surface of the scapula, courses laterally beneath the coracoid, and becomes tendinous near the level of the glenoid rim. The tendinous footprint is roughly trapezoidal in shape, with its widest portion superior, and has a mean superior to inferior length of 2.5 cm.[8]

Macroscopically, the superior two-thirds of the subscapularis ends as a tendon that inserts on the lesser tuberosity of the humerus. The inferior part has no tendon; the muscle attaches directly to the bone, as with the teres minor on the posterior aspect of the humerus. Due to anatomical, biomechanical but also electrophysiological considerations, the subscapularis muscle, usually perceived as a single muscle, should be considered as two different muscles (inferior and superior).[9]

The superior and inferior subscapularis are innervated by two different nerves.11,12 The superior part is innervated by the upper subscapularis nerve that comes directly from the posterior cord. The inferior part is innervated by the lower subscapularis nerve arising from either the axillary nerve or the thoracodorsal nerve.[10] [11]

Electrophysiology studies confirm this division and have shown different activity in the superior and inferior parts of the subscapularis.[12]

Different activation patterns in the two parts of the subscapularis are also found during a positron emission tomography (PET) study.[13]

The superior margin of the subscapularis marks the inferior border of the rotator interval, which contains the superior glenohumeral ligament and the coracohumeral ligament. The medial sling, composed of a robust deep layer (medial head of the coracohumeral ligament) and a thin superficial layer (superior glenohumeral ligament), has an insertional footprint at the top of the lesser tuberosity that is directly adjacent to the footprint of the superolateral subscapularis on the lesser tuberosity. As such, when the upper subscapularis tears away from its bone attachment, the medial sling (which is directly adjacent to it), also tears away from the bone. As this sling is part of the bicipital pulley, biceps pathology is frequently associated with subscapularis tears.

Biomechanics

The subscapularis is the largest and most powerful of the rotator cuff muscles, providing more than 50% of the rotator cuff force alone.[14]

Functionally, the subscapularis internally rotates the humerus, contributes to anterior stability of the shoulder, and plays an important role in balancing force couples of the glenohumeral joint. In the coronal plane, the superior deltoid moment is balanced by the inferomedial moment of the inferior rotator cuff (Figure).

Figure. 1 Balanced force couples are required to maintain the normal glenohumeral relationship. In the coronal plane the combined inferior rotator cuff force (C) is balanced against the deltoid (D).

In the transverse plane, the subscapularis anteriorly is balanced with the infraspinatus and teres minor posteriorly (Figure).[15][16][17]

Figure. 2 In the transverse plane the subscapularis (S) is balanced against the infraspinatus and teres minor (I). O, center of rotation; A, moment arm of the deltoid; a, moment arm of the inferior rotator cuff; r, moment arm of the subscapularis; R, moment arm of the infraspinatus and teres minor.

Muscle activation of the subscapularis tendon has been shown to be higher in patients with asymptomatic rotator cuff tears, demonstrating that the subscapularis tendon plays an important role in compensating for posterosuperior rotator cuff tears.[18]

Additionally, the anterior attachment of the rotator cable extends to the upper subscapularis insertion.[19]

Maintenance of the subscapularis footprint is thus integral to normal biomechanical function of the shoulder. Finally, repair of the upper subscapularis decreases the stress on the adjacent repair of the supraspinatus, thereby protecting repair of the latter.[20]

It is thus important to be adept at recognizing and treating these tears.

The subscapularis is crucial for shoulder elevation. Effectively, pseudoparalysis is almost always correlated to subscapularis tears (Figure). This is particularly the case when tears involve the lower half of the subscapularis tendon. Therefore, treatment of large cuff tears should include subscapularis repair to avoid the anterior extension of the tear and development of pseudoparalysis.[21]

Figure. 3 Percentage of pseudoparalysis, which is defined as the inability to elevate the arm actively beyond 90 degrees with full passive range of motion. Observe the high rate of pseudoparalysis in case of massive rotator cuff tears involving the subscapularis (B and C massive rotator cuff tears). Reproduce from Collin et al., with permission.


History and Physical Examination

The etiology of subscapularis tears can be traumatic or non-traumatic. Traumatic tears are infrequent and typically occur in younger patients resulting from forced hyperextension or forced external rotation with the arm either at the side or in a position of abduction.[22]

Non-traumatic tears are probably related to intrinsic degeneration, long head of the biceps instability, as well as anterosuperior impingement that occurs against the anterosuperior glenoid rim during flexion and internal rotation.[23]

The pain is typically located more anteriorly compared to posterosuperior rotator cuff tears and can radiate down the arm. Difficulty with activities of daily living are common, particularly with reaching behind and reaching across the body.

On physical examination palpation is not specific. Pain may be provoked with anterior elevation and internal rotation. The classic finding of increased passive external rotation compare to the other side, does not typically occur without a complete tear. Strength testing may reveal pain or decreased power with resisted internal rotation. Several special tests have been described to aid in diagnosis, including the lift-off, belly-press, and bear-hug tests.

Lift-off

The lift-off test is performed by placing the hand behind the back and asking the patient to internally rotate the arm to lift the hand posterioly off the back. Placing the arm behind the back isolates the subscapularis as an internal rotator. The test is considered positive if the patient is unable to lift the arm off the back.[24]

Belly-press

The belly-press is performed by placing the palm on the navel with the wrist in a neutral position. In a positive test the wrist flexes and the elbow moves posteriorly as the patient actively extends the shoulder by means of the posterior deltoid to maintain the palm position. One advantage of the belly-press compared to the lift-off test as the latter requires to put the hand of the patient in the back, manoeuver that is often painful.[25]

Bear-hug

The bear-hug test is performed by placing the palm on the contralateral shoulder with the fingers extended and the arm in approximately 45 degrees of forward flexion (Figure). The position is maintained while the examiner attempts to pull the forearm away from the shoulder in a perpendicular manner. A positive test is indicated by weakness with this maneuver, in which the examiner is able to pull the patient’s hand away from the shoulder.[26]

Figure. 4 The bear-hug test. The hand on the affected side is placed on the opposite shoulder with the fingers extended and the elbow flexed forward. The patient resists as the examiner tries to pull the hand off the shoulder in a direction that is perpendicular to the plane of the forearm (arrow). If the examiner is able to lift the hand off the shoulder, the patient likely has a torn (either partial or complete) upper subscapularis tendon.


Imaging

X-ray

Three views of the shoulder (anteroposterior views in neutral rotation, axillary view, outlet view) should be obtain. Most patients will have normal radiographs. Although uncommon, lesser tuberosity cysts on plain radiographs have been reported to have an 87% specificity for subscapularis tears.[27]

In massive tears, patients may demonstrate proximal migration of the humerus.

Ultrasound

Ultrasound (US) can used as a non-invasive test to screen for subscapularis tears. However, the sensitivity of this methodology is also low.[28]

Using ultrasound imaging, the subscapularis tendon is best visualised with the shoulder in external rotation, elbow kept firmly by the thorax (Figure), drawing the tendon out from beneath the coracoid process. While looking at the tendon’s long axis, its integrity can be analyzed, as well as its relationship with surrounding structures by dynamically performing internal and external rotation of the shoulder. Examination of the short axis of the tendon (by rotating the probe by 90 degrees) reveals its multifascicular pattern, and allows complete analysis from its upper border (with the biceps tendon lying supero-laterally), where injuries often begin, to its lower border.[29]

Figure. 5 Ultrasound is also very helpful to detect a dynamic instability of the long head of the biceps (Figure). Reproduced from Plomb-Holmes et al., with permission.


Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is used to characterize the subscapularis tear, retraction, fatty infiltration according to Goutallier, and provides information about concominant pathology. However, it is important to note that the sensitivty for detection is often low; in some studies the sensitiviy is below 50%. Therefore a high index of suspicion should be maintianed and mulitple views should be analyzed to increas the chance of detection.

30. 8-83. 29. Adams CR, Brady PC, Koo SS, et al. A systematic approach for diagnosing subscapularis tendon tears with preoperative magnetic resonance imaging scans. Arthroscopy 2012;28:1592-600.

Axial View

Classically, the subscapularis is best evaluated on T2 the axial views. Complete tears demonstrate a bare lesser tuberosity with a retracted tendon margin (Figure).

Figure. 6 T-2 weighted axial magnetic resonance images demonstrating subscapularis tears. Complete retracted tear (yellow arrow, retracted tendon edge) with narrowed coracohumeral interval (yellow line).

Increased signal in the tendon on T2 images without retraction can indicate a partial tear (Figure).

Figure. 7 Partial tear with increased signal at the subscapularis insertion at the lesser tuberosity. Observe the medial biceps subluxation that is pathonomoic for a subscapularis tear.

Saggital view

T1 saggital view is also important to review, particularly to analyse the bicipital pulley and subtle anterior dislocation of the long head of the biceps in type in type-I to type-II subscapular tears. Furthermore, fatty degeneration of the upper half of the subscapularis tendon on this view is a tell-tale sign of a tear of the subscapularis (Figure).

Figure. 8 T1 saggital view. A) Long head of the biceps (asterix) and coracohumeral ligament (white arrow). B) Long head of the biceps (asterix) interposed between the subscapularis tendon (white arrows) and the smaller tuberosity, indicating a subscapularis lesion. C) Grade 4 fatty infiltration of the upper subscapularis (black arrow).

Coronal view

On coronal oblique images, normal appearance usually shows four (rarely up to six) digitations and their insertion on the lesser tuberosity over the bicipital groove.[30][31]

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Types of Lesions and Tear Classifications

Lateral Disruption and Associated Lesions

Identifying the subscapularis tendon stump is the key to determine the type of lesion and how to treat them. The upper border of a normal subscapularis tendon is a smooth and regular. Any delamination is a sign of failure (Video).


A particular type of superior abrasion is part of anterosuperior impingement (FUSSI or SAM lesion). Please also refer below and to anterior impingement chapter.[32]

The subscapularis tendon has several lesion patterns:

A) The tear of the subscapularis can be vertical, caused by a portion of the superior glenohumeral ligament/coracohumeral ligament complex that has torn off the humerus, forming the comma sign of Lo and Burkhart.33 The tendon is then retracted medially (medial retraction) and the structure observed in front of the shoulder consist of ligaments (Figure).[33]

References

  1. ↑ Collin P, Matsumura N, Lädermann A, Denard PJ, Walch G. Relationship between massive chronic rotator cuff tear pattern and loss of active shoulder range of motion. J Shoulder Elbow Surg 2014;23:1195-202.
  2. ↑ Denard PJ, Lädermann A, Jiwani AZ, Burkhart SS. Functional outcome after arthroscopic repair of massive rotator cuff tears in individuals with pseudoparalysis. Arthroscopy 2012;28:1214-9.
  3. ↑ Walch G, Nové-Josserand L, Liotard JP, Noel E, Tavernier TH, Barthélémy R. Le petit rond (teres minor): l'oublié de la coiffe. In: Blum A TT, Brasseur J-L, Noël E, Walch G, Cotten A, Bard HG,, ed. L'Epaule: une approche pluridisciplinaire. Montpellier:: Sauramps Medical; 2005:237–44.
  4. ↑ Arai R, Sugaya H, Mochizuki T, Nimura A, Moriishi J, Akita K. Subscapularis tendon tear: an anatomic and clinical investigation. Arthroscopy 2008;24:997-1004.
  5. ↑ Barth JR, Burkhart SS, De Beer JF. The bear-hug test: a new and sensitive test for diagnosing a subscapularis tear. Arthroscopy 2006;22:1076-84.
  6. ↑ Bennett WF. Subscapularis, medial, and lateral head coracohumeral ligament insertion anatomy. Arthroscopic appearance and incidence of "hidden" rotator interval lesions. Arthroscopy 2001;17:173-80.
  7. ↑ Lafosse L, Jost B, Reiland Y, Audebert S, Toussaint B, Gobezie R. Structural integrity and clinical outcomes after arthroscopic repair of isolated subscapularis tears. J Bone Joint Surg Am 2007;89:1184-93.
  8. ↑ Richards DP, Burkhart SS, Tehrany AM, Wirth MA. The subscapularis footprint: an anatomic description of its insertion site. Arthroscopy 2007;23:251-4.
  9. ↑ Collin P, Lädermann A, Le Bourg M, Walch G. Subscapularis minor--an analogue of the Teres minor? Orthopaedics & traumatology, surgery & research : OTSR 2013;99:S255-8.
  10. ↑ Kadaba MP, Cole A, Wootten ME, et al. Intramuscular wire electromyography of the subscapularis. J Orthop Res 1992;10:394-7.
  11. ↑ Kasper JC, Itamura JM, Tibone JE, Levin SL, Stevanovic MV. Human cadaveric study of subscapularis muscle innervation and guidelines to prevent denervation. J Shoulder Elbow Surg 2008;17:659-62.
  12. ↑ Kadaba MP, Cole A, Wootten ME, et al. Intramuscular wire electromyography of the subscapularis. J Orthop Res 1992;10:394-7.
  13. ↑ Omi R, Sano H, Ohnuma M, et al. Function of the shoulder muscles during arm elevation: an assessment using positron emission tomography. Journal of anatomy 2010;216:643-9.
  14. ↑ Keating JF, Waterworth P, Shaw-Dunn J, Crossan J. The relative strengths of the rotator cuff muscles. A cadaver study. J Bone Joint Surg Br 1993;75:137-40.
  15. ↑ Burkhart SS. Fluoroscopic comparison of kinematic patterns in massive rotator cuff tears. A suspension bridge model. Clin Orthop Relat Res 1992:144-52.
  16. ↑ Burkhart SS. Reconciling the paradox of rotator cuff repair versus debridement: a unified biomechanical rationale for the treatment of rotator cuff tears. Arthroscopy 1994;10:4-19.
  17. ↑ Hansen ML, Otis JC, Johnson JS, Cordasco FA, Craig EV, Warren RF. Biomechanics of massive rotator cuff tears: implications for treatment. J Bone Joint Surg Am 2008;90:316-25.
  18. ↑ Kelly BT, Williams RJ, Cordasco FA, et al. Differential patterns of muscle activation in patients with symptomatic and asymptomatic rotator cuff tears. J Shoulder Elbow Surg 2005;14:165-71.
  19. ↑ Burkhart SS, Esch JC, Jolson RS. The rotator crescent and rotator cable: an anatomic description of the shoulder's "suspension bridge". Arthroscopy 1993;9:611-6.
  20. ↑ Ticker JB, Burkhart SS. Why repair the subscapularis? A logical rationale. Arthroscopy 2011;27:1123-8.
  21. ↑ Collin P, Matsumura N, Lädermann A, Denard PJ, Walch G. Relationship between massive chronic rotator cuff tear pattern and loss of active shoulder range of motion. J Shoulder Elbow Surg 2014;23:1195-202.
  22. ↑ Gerber C, Krushell RJ. Isolated rupture of the tendon of the subscapularis muscle. Clinical features in 16 cases. J Bone Joint Surg Br 1991;73:389-94.
  23. ↑ Gerber C, Sebesta A. Impingement of the deep surface of the subscapularis tendon and the reflection pulley on the anterosuperior glenoid rim: a preliminary report. J Shoulder Elbow Surg 2000;9:483-90.
  24. ↑ Gerber C, Krushell RJ. Isolated rupture of the tendon of the subscapularis muscle. Clinical features in 16 cases. J Bone Joint Surg Br 1991;73:389-94.
  25. ↑ Gerber C, Hersche O, Farron A. Isolated rupture of the subscapularis tendon. J Bone Joint Surg Am 1996;78:1015-23.
  26. ↑ Barth JR, Burkhart SS, De Beer JF. The bear-hug test: a new and sensitive test for diagnosing a subscapularis tear. Arthroscopy 2006;22:1076-84.
  27. ↑ Studler U, Pfirrmann CW, Jost B, Rousson V, Hodler J, Zanetti M. Abnormalities of the lesser tuberosity on radiography and MRI: association with subscapularis tendon lesions. AJR American journal of roentgenology 2008;191:100-6.
  28. ↑ Singisetti K, Hinsche A. Shoulder ultrasonography versus arthroscopy for the detection of rotator cuff tears: analysis of errors. Journal of orthopaedic surgery 2011;19:76-9.
  29. ↑ Plomb-Holmes C, Clavert P, Kolo F, Tay E, Ladermann A, French Society of A. An orthopaedic surgeon's guide to ultrasound imaging of the healthy, pathological and postoperative shoulder. Orthop Traumatol Surg Res. 2018 Dec;104(8S):S219-S232.27.
  30. ↑ Cash CJ, MacDonald KJ, Dixon AK, Bearcroft PW, Constant CR. Variations in the MRI appearance of the insertion of the tendon of subscapularis. Clin Anat 2009;22:489-94.
  31. ↑ In the case of Lafosse III-V subscapularis tears, one or more of the pennate muscular components may present a structural distortion, up to a total absence of the tendon structure with the presence of only fluid-type signal. This radiological sign is called the digitation sign (Figure) (unpublished data from Lionel Neyton).
  32. ↑ Brady PC, Grubbs H, Lädermann A, Adams CR. Middle Glenohumeral Ligament Abrasion Causing Upper Subscapularis Tear. Arthrosc Tech 2017;6:e2151-e4.
  33. ↑ Lo IK, Burkhart SS. The comma sign: An arthroscopic guide to the torn subscapularis tendon. Arthroscopy 2003;19:334-7.
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