Middle Glenohumeral Ligament Abrasion Causing Upper Subscapularis Tear.

The middle glenohumeral ligament (MGHL) typically contributes partially to the anterior stability of the shoulder. In a very limited number of cases, the MGHL can cause abrasion on the upper edge of the subscapularis causing persistent pain symptoms for patients. The condition is exacerbated by internal rotation of the arm. In this Technical Note, we describe this entity and call it the SAM lesion (Subscapularis Abrasion from the MGHL). We present a technique of addressing this lesion.

With the evolution of arthroscopic shoulder surgery, our understanding of normal and pathologic shoulder conditions continues to advance. The subscapularis has increasingly been recognized as a potential source of shoulder pathology and pain. Studies have shown subscapularis pathology in up to 37% of rotator cuff tears.1, 2

Several members of the BRASS research group have noticed an arthroscopic finding in a limited number of patients related to upper subscapularis tearing and/or fraying. Specifically it is an entity in which the middle glenohumeral ligament (MGHL) abrades against the upper edge of the subscapularis medial to its insertion at the lesser tuberosity. Anatomic studies have shown the close relation of the MGHL to the upper subscapularis near its insertion into the lesser tuberosity of the humerus.3, 4 In the lesion we describe in this Technical Note, the MGHL compresses into the upper edge of the subscapularis causing pain and intra-articular pathology. We have used the acronym of the SAM lesion for Subscapularis Abrasion from the MGHL.

The MGHL has been found to contribute to anterior stability when the arm is in 0° to 45° of abduction, and the strain on the ligament is decreased as the arm continues to 90° of abduction. However, although sectioning has been shown to allow for increased excursion of the humeral head, this has not been shown to contribute to clinical anterior instability.

In this Technical Note, we describe both the entity of subscapularis abrasion from the MGHL (SAM lesion) and our technique of addressing this pathologic lesion.

Surgical Technique

Preoperative Assessment

Preoperatively these patients have presented somewhat of a diagnostic conundrum for us. They frequently have vague and nondescript anterior shoulder pain. Imaging studies including magnetic resonance imaging and radiographs are typically nondiagnostic. Symptoms are primarily reproduced with resisted internal rotation of the shoulder with pain with subscapularis testing including the bear hug, belly press, lift off, and Napoleon examinations. However, these patients often have normal strength with these same tests. The biceps examination is typically equivocal and often biceps pathology is suspected in these patients because of their symptoms of primarily anterior shoulder pain with activities.

Operative Setup

After general anesthesia and administration of preoperative antibiotics, patients are positioned in the lateral decubitus position and the shoulder prepped and draped in the usual sterile fashion.

Portal Placement

A posterior portal is used and diagnostic arthroscopy performed. After the intra-articular diagnostic portion of the procedure is completed, a low anterior portal and an anterosuperolateral portal are created. These 2 anterior portals will be used as the working portals as the visualization is entirely from the posterior portal.

Diagnostic Arthroscopy

During this portion of the procedure, the anterior structures of the shoulder are visualized and dynamically examined with internal rotation and flexion of the humerus (Video 1, Table 1). On initial inspection of the upper border of the subscapularis, an abrasion lesion or a tendon indentation and/or partial tearing is noted approximately 1 to 2 cm medial to the articular insertion of the upper subscapularis on the lesser tuberosity bone bed. The lesion is in close approximation to the lateral edge of the MGHL (Fig 1A). Typically with internal rotation of the humerus, the MGHL is seen “cutting” into the upper boarder of the subscapularis (Fig 1B). Frequently, the MGHL will have a relatively sharpened edge that can clearly be seen as the pathologic lesion creating the upper subscapularis pathology.

Table 1

Identification of the MGHL Arthroscopically

• A standard 30° arthroscope is inserted into the posterior portal. • After pump pressure stabilizes and visual field clears, inspection of the anterior aspect of the shoulder joint proceeds. • The subscapularis tendon is identified anteriorly traveling from medial to lateral at the mid to upper quadrant of the glenoid. • The subscapularis should be visually examined as far medial as the arthroscopic view will allow and all the way to its insertion on the lesser tuberosity of the humerus. • The scope should be withdrawn slightly to allow visualization of the insertion site of the long head of the biceps on the superior glenoid tubercle. • The MGHL originates just anterior to the long head of the biceps insertion along with the anterior superior labrum and travels in an inferior-lateral direction to insert into the inferior portion of the humeral head underneath the lower portion of the subscapularis tendon. • The MGHL can have varying appearances including broad, thin, cord-like, or absent. • The MGHL can also be a “Buford complex” in which the anterior labrum is absent superiorly and the MGHL originates directly from the superior glenoid tubercle and immediately becomes cord-like and travels inferior and lateral.

MGHL, middle glenohumeral ligament.

Fig 1

(A) Posterior portal view of the right shoulder with a 30° arthroscope. The humeral head (H) is on the lower right. The MGHL (labeled) sits approximately 1 cm medial to a significant abrasion lesion of the upper boarder of the subscapularis (∗). (B) Posterior portal view of the right shoulder with a 30° arthroscope. The glenoid (G) is visible on the left side of the field of view. With internal rotation of the humerus, the MGHL (labeled) can clearly be seen to be the offending lesion cutting into the upper subscapularis causing the pathology in the subscapularis. (MGHL, middle glenohumeral ligament.)

Surgical Technique

After completion of the intra-articular diagnostic arthroscopy, an anterosuperolateral and/or anterior portal are created. Through this anterior portal, the edge (and usually the entirety) of the MGHL is divided with arthroscopic scissors, shaver (Arthrex, Naples, FL), electrocautery (Arthrex), or combination of the above (Fig 2). This is divided in a lateral to medial direction just at the superior margin of the subscapularis, thus cutting the MGHL in its midsubstance (Table 2).

Fig 2

(A) Posterior portal view of the right shoulder with a 30° arthroscope. An anterior portal is created and curved arthroscopic scissors (Arthrex) are used to divide the MGHL just over top of the upper subscapularis (SSc) tendon. The humeral head (H) is visible on the lower right. (B) Posterior portal view of the right shoulder with a 30° arthroscope. An arthroscopic shaver (Arthrex) is also used to assure complete excision of the MGHL (∗) over the top and front of the subscapularis (SSc). The humeral head (H) is visible in the lower right. (MGHL, middle glenohumeral ligament.)

Table 2

Technique Pearls and Pitfalls

Pearls	Pitfalls
• Recognize normal MGHL anatomy • Perform a dynamic examination during diagnostic arthroscopy (internal and external humeral rotation) • Divide compressing MGHL through its midsubstance • Assure that the entire offending lesion is released by repeating dynamic examination during arthroscopy • Must address any additional shoulder pathology	• Failure to thoroughly evaluate the entire subscapularis tendon • Simple debridement of an upper subscapularis abrasion without determining and addressing the offending lesion • Incomplete transection of the MGHL • Failing to re-evaluate the anterior structures after MGHL division

MGHL, middle glenohumeral ligament.

Assessment After Addressing the Lesion

The anterior aspect of the shoulder is then re-examined and rotation of the humerus performed to confirm that the previous lesion is now adequately addressed (Fig 3). There should now be no abrasion of the MGHL against the upper boarder of the subscapularis.

Fig 3

Posterior portal view of the right shoulder with a 30° arthroscope. After complete release and excision of the middle glenohumeral ligament, the offending lesion on the subscapularis (SSc) is clearly removed and the upper subscapularis contour returns to near normal. The humeral head is in the lower right.

Addressing Remainder of Shoulder

Particular care is also taken to thoroughly examine the remainder of the intra-articular structures in the anterior aspect of the shoulder. The long head of the biceps tendon is palpated with a probe, and a portion pulled into the joint for further examination. The subcoracoid space is examined to assure that there is no subcoracoid impingement, and if this is encountered, a coracoplasty is performed. If the patient had any preoperative symptoms of acromioclavicular joint involvement, then this joint is addressed with an arthroscopic distal clavicle excision.

Rehabilitation

If additional pathology encountered and addressed at the time of arthroscopy is limited or nonexistent, then we allow these patients to begin immediate shoulder mobilization. Once range of motion is functional, then strengthening and resumption of normal shoulder activity is begun.

Discussion

We have described MGHL abrasion causing upper subscapularis pathology. We have termed this pathology as the SAM lesion.

A similar shoulder pathologic entity of a frayed upper subscapularis with impingement (or FUSSI) lesion has been described by the SCOI group in an online educational video; however, the pathology we describe differs in several ways. First, the FUSSI lesion is described as a capsular reflection causing abrasion, whereas we describe the MGHL as being the offending structure. Second, the lesion caused by the capsular reflection is typically quite medial and often not visible from the posterior portal with a standard arthroscope, whereas the condition we describe is always visible from the posterior portal because the pathology lies at the level of (or lateral to) the MGHL. Third, the abrasion of the subscapularis caused by the capsular reflection is noted to be worse with external rotation. However, with the SAM lesion, the MGHL compresses the upper subscapularis with internal rotation. Lastly, the FUSSI lesion is reported to always occur with subacromial impingement. This is seldom a clinical or surgical finding with our patients.

In the cases we have seen, the MGHL has typically appeared relatively normal. However, in one case (presented in Video 1), the MGHL was somewhat cord-like. Often, the lateral edge of the MGHL appears somewhat sharper than is typical and thus may contribute to the subscapularis abrasion. We have not seen significant detriment to the excision and removal of the MGHL in these patients.

Although our results have been excellent with this procedure, sectioning of the MGHL could have potential negative repercussions (Table 3). These could include destabilization of the glenohumeral joint. Although we believe that the risk is minimal, it could be more apparent in patients with some degree of pre-existing instability. Another limitation of this technique is that it should not exclude a thorough examination of all potential contributing factors of anterior shoulder pain. Surgeons should be very vigilant to thoroughly examine each structure in the shoulder for its integrity and potential contribution to a patient's shoulder pain. Despite these potential limitations in this procedure, we believe that knowledge of and examination for this potential pathology is an important aspect in the arthroscopic assessment and management of patients with anterior shoulder pain.

Table 3

Technique Advantages and Disadvantages

Advantages	Disadvantages
• The evaluation and diagnosis are simple and straightforward • Addresses a potential cause of anterior shoulder pain • Eliminates future potential damage to the upper edge of the subscapularis	• Potential destabilization in patients with laxity • If substantial damage has occurred to the subscapularis, additional repair may be necessary

We believe that surgeons should evaluate for the SAM lesion when they perform shoulder arthroscopy on patients with anterior shoulder pain. When abrasion of the upper subscapularis is identified arthroscopically, the MGHL may be a contributor to the pathology.