Arthroscopic Management of Anterior Instability: Pearls, Pitfalls, and Lessons Learned

Despite advances in the understanding of anterior shoulder instability, failure rates after open and arthroscopic surgery have been reported to be as high as 30%. In general, a successful operative outcome for patients with shoulder instability requires the surgeon to perform a complete preoperative evaluation, a thorough diagnostic arthroscopy to evaluate for concomitant co-pathology, and implement an effective postoperative therapy program tailored to the repair strategy. In addition to the Bankart lesion, the treating surgeon must be aware of other co-pathologies, such as the HAGL lesion, ALPSA lesion, and SLAP tears, that can occur in concert with capsular pathology and present as potential barriers to a successful outcome. This article focuses specifically on the pearls and pitfalls that are important to recognize in the preoperative workup, intraoperative evaluation, and arthroscopic surgery to optimize surgical outcomes for anterior instability.

The diagnosis and treatment of recurrent anterior shoulder instability continue to evolve. Although open capsular plication with Bankart repair has long been considered the optimal method for surgical management of shoulder instability, advancements in arthroscopic techniques have led to a recent shift to arthroscopic Bankart repair. Advances in instrumentation and implants coupled with the ability to produce more of an open type of arthroscopic repair have all led to improved results with the arthroscopic technique.

To obtain a successful outcome for patients with anterior instability, it is imperative that the surgeon be aware of preoperative, intraoperative, and postoperative factors associated with the recognition and proper treatment of instability pathology. In this article, the authors present several important pearls and pitfalls of how to effectively diagnose and treat patients with recurrent anterior instability using arthroscopic techniques. In addition, the authors highlight the importance of the recognition of anterior instability pathology and provide the important principles for successful arthroscopic management.

Anatomy

Improvements in our understanding of the biomechanical and pathoanatomical features of anterior shoulder instability have led to advances in clinical diagnosis and recognition of associated pathology. The stability of the glenohumeral joint is conferred by three major mechanisms: (1) concavity-compression, (2) coordinated contraction of the rotator cuff to permit fluid and complete range of motion of the humeral head onto the glenoid surface, and (3) contribution of the glenohumeral ligaments. When considering instability, the most pertinent anatomy includes the dynamic and static stabilizers of the shoulder joint. The static stabilizers include the bony anatomy, capsular ligaments, and the rotator interval, whereas the dynamic stabilizers include the rotator cuff and scapular rotator musculature ( Fig. 1 ).

→ Pearl: Understand the pathoanatomy of anterior shoulder instability.

The glenohumeral capsuloligamentous complex serves to statically restrain the glenohumeral joint against excessive translation in varying positions of arm rotation. The anterior band of the inferior glenohumeral ligament (AIGHL) attaches to the glenoid at the anteroinferior labrum and is the primary static restraint to anterior translation in the abducted externally rotated shoulder.

The bony anatomy of the glenohumeral joint plays a major role in anterior shoulder stability. Because of the small size of the glenoid compared with the humeral head, even a small loss of bone, such as a glenoid rim fracture, can compromise stability by decreasing the bony surface area for glenohumeral articulation. Several clinical studies have shown that bone loss of either the humeral head or glenoid surface is the most common cause of failed arthroscopic stabilization procedures and that recurrence of glenohumeral instability is increased when there is 15% to 20% glenoid bone loss.

The labrum is the portion of fibrocartilage that is circumferentially attached to the rim of the glenoid. It is critical for the orthopedic surgeon to recognize the normal anatomy and anatomic variants of the labrum to prevent misdiagnoses and inadvertent treatment. The anteroinferior attachment of the labrum to the glenoid rim is normally tight, and injury to this structure is typically referred to as the essential lesion, or the Bankart lesion ( Fig. 2 ). The normal superior attachment of the labrum to the glenoid is loose, has tremendous anatomic variation, and is complicated by the attachment of the long head of the biceps tendon as it originates from the supraglenoid tubercle. The function of the labrum as it relates to stability of the shoulder joint is threefold. First, the labrum deepens the concavity of the glenoid up to 9 mm in the superior-inferior direction and also doubles the anteroposterior depth to 5 mm. Second, the labrum increases glenohumeral stability by increasing the surface area through which the glenoid contacts the humeral head through an arc of motion. Finally, the labrum is the site of attachment for the various glenohumeral ligaments that confer static stability to the joint.

→ Pearl: A comprehensive evaluation of the scapular and rotator cuff musculature is important because dynamic stability is critical to glenohumeral function.

The rotator cuff musculature and parascapular muscles are critical to the overall function of the glenohumeral joint and confer important dynamic stability to the shoulder. A careful evaluation of the rotator cuff (especially in patients who present with an initial dislocation more than 40 years old) and scapular function is paramount to ensure that the dynamic stability of the glenohumeral joint is optimized.

There are several other intra-articular lesions associated with anterior instability and include a superior labral anterior posterior lesion, which is a detachment of the glenoid labrum at the insertion of the long head of the biceps tendon; a medial displacement of the labrum and periosteal sleeve of the anterior glenoid labrum and capsule (Anterior Labral Periosteal Sleeve Avulsion [ALPSA]); and the humeral avulsion of the glenohumeral ligament or detachment of the capsuloligamentous structures off the humeral head (HAGL lesion). See the article by Boselli and colleagues elsewhere in this issue for a thorough review of these lesions. The presence of these lesions can lead to recurrent instability and future subluxation events if not properly addressed.

Patient history

Understanding the source and type of instability that patients are experiencing is critical to the ultimate success of surgical treatment. A thorough history should always include type of instability (dislocation, subluxation); direction of instability (anterior, posterior, multidirectional); requirement for medically assisted reduction versus self-reduction; age and amount of time that had elapsed from the first dislocation; activity level, including contact versus non-contact sports; and any treatment that has been rendered to date.

→Pearl: if patients experience an initial dislocation at more than 40 years of age, it is imperative to rule out an associated rotator cuff tear.

In addition, the provocative anterior instability position (almost always the abducted externally rotated position) and the amount of trauma necessary for the instability episode to occur has implications in management. Patients whose shoulders slip out during sleep or with simple activities, such as reaching overhead, may have an entirely different diagnosis (ie, multidirectional instability, glenoid hypoplasia, and so forth) and may require a different surgical plan compared with those who experience instability only with more significant trauma. If patients demonstrate the ability to easily dislocate the shoulder they should be closely evaluated for a volitional component, especially in the absence of glenoid bone loss, glenoid dysplasia, connective tissue disorders, or prior surgery.

Patients with anterior shoulder instability most often present with feelings of impending instability or pain in extremes of motion, and may experience subluxation or even frank dislocation during certain shoulder positions (namely abduction and external rotation and with overhead activities). Although most patients complain of subjective feelings of instability during repetitive overhead activities, such as throwing or swimming, some patients may present with reports of transient sharp pain, numbness, or weakness that usually resolves briefly as their only symptom of instability.

Patient history

Understanding the source and type of instability that patients are experiencing is critical to the ultimate success of surgical treatment. A thorough history should always include type of instability (dislocation, subluxation); direction of instability (anterior, posterior, multidirectional); requirement for medically assisted reduction versus self-reduction; age and amount of time that had elapsed from the first dislocation; activity level, including contact versus non-contact sports; and any treatment that has been rendered to date.

→Pearl: if patients experience an initial dislocation at more than 40 years of age, it is imperative to rule out an associated rotator cuff tear.

In addition, the provocative anterior instability position (almost always the abducted externally rotated position) and the amount of trauma necessary for the instability episode to occur has implications in management. Patients whose shoulders slip out during sleep or with simple activities, such as reaching overhead, may have an entirely different diagnosis (ie, multidirectional instability, glenoid hypoplasia, and so forth) and may require a different surgical plan compared with those who experience instability only with more significant trauma. If patients demonstrate the ability to easily dislocate the shoulder they should be closely evaluated for a volitional component, especially in the absence of glenoid bone loss, glenoid dysplasia, connective tissue disorders, or prior surgery.

Patients with anterior shoulder instability most often present with feelings of impending instability or pain in extremes of motion, and may experience subluxation or even frank dislocation during certain shoulder positions (namely abduction and external rotation and with overhead activities). Although most patients complain of subjective feelings of instability during repetitive overhead activities, such as throwing or swimming, some patients may present with reports of transient sharp pain, numbness, or weakness that usually resolves briefly as their only symptom of instability.

Physical examination

After obtaining the appropriate history from patients, a complete physical examination is integral to making the correct diagnosis and implementing the appropriate treatment plan. Range of motion, neurovascular examination, and overall strength (shoulder girdle and parascapular muscles) should all be normal in the majority of patients with shoulder instability. Specific provocative tests are the hallmark of assessing anterior shoulder instability, including the apprehension, relocation, and anterior release tests. Especially important to investigate is the ease with which the humerus begins to dislocate and engage on the glenoid; if this occurs at 30° of external rotation at the side, for example, it is highly likely that there is a significant engaging Hill-Sachs lesion or associated glenoid bone loss. Patients with engaging Hill-Sachs lesions also usually report a history of shoulder instability in midranges of the shoulder abduction/external rotation.

It is imperative that the surgeon discerns between laxity and instability. Instability is generally regarded as symptomatic laxity and is the perception by patients experiencing the shoulder subluxation or dislocation event. Laxity is a normal finding of the glenohumeral joint, because the humerus needs to have a minimum obligate translation on the glenoid for normal shoulder function. The amount of laxity and instability are both assessed with translation testing for laxity (anterior, posterior, and inferior sulcus) and symptomatic directional laxity, which is a critical diagnostic indicator of shoulder instability. A positive sulcus sign that does not decrease with external rotation at the side indicates a pathologic rotator interval ( Fig. 3 ). Increased generalized ligamentous laxity should also be assessed, including thumb to forearm, elbow recurvatum, metacarpophalangeal hyperextension, and increased external rotation in the abducted position.

Radiographic evaluation

Upon initial evaluation of patients with a traumatic shoulder dislocation, routine radiographs should be obtained, including true anteroposterior, axillary lateral, and scapular-Y views. In patients with a history of recurrent anterior instability, or if a bone defect is suspected, further radiographic imaging is warranted, including the apical oblique, West Point view, or Didiee views. For humeral head defects, such as a Hill-Sachs injury, the Stryker Notch view and a true anteroposterior in internal rotation should be obtained. Hill-Sachs injuries may be well demonstrated on anteroposterior internal rotation views ( Fig. 4 ).

Evaluation of glenoid and humeral head bone loss

In evaluating patients with glenohumeral instability, it essential that the surgeon assess for patient demographic and examination factors associated with glenoid and humeral head bone loss. Patients with high energy trauma to the shoulder leading to dislocation should be evaluated for glenoid bone loss. The position when instability of the shoulder is first experienced should be carefully assessed on examination to determine if the instability is present in midranges of motion (suggestive of bone loss).

→ Pearl: Patients that present with numerous instability episodes, a long history of instability, or progressive ease of instability symptoms suggests a larger anatomic problem, namely glenoid or humeral head bone loss.

→Pearl: Patients who demonstrate instability in midranges of motion (45° abduction with external rotation), have a progressive ease of instability symptoms, or have a long, documented history of recurrence, should be evaluated closely for glenoid or humeral head bone loss.

For a comprehensive evaluation of glenoid bone loss, advanced imaging is necessary. An MRI and MR Arthrogram, although helpful in diagnosis of soft-tissue pathology, may also be used to assess the degree of bone loss by evaluating the most lateral glenoid cut on sagittal oblique images ( Fig. 5 ). However, the most accurate method to measure glenoid bone loss is a three-dimensional CT scan with digital subtraction of the humeral head on sagittal oblique imaging. The humeral head may also be isolated in three-dimensional reconstruction to assess the size, depth, and orientation of the Hill-Sachs defect.

→ Pearl: Nearly all patients with recurrent anterior instability have some amount of glenoid bone loss (either of glenoid, humeral head, or both) and the surgeon should seek to determine the extent of bone loss to make informed decisions regarding optimal treatment.

Huysmans and colleagues have described the inferior two thirds of the glenoid as a well-conserved circle, and deficiencies within this circle are used to quantify the amount of glenoid bone loss. ( Fig. 6 ) A best-fit circle is drawn on the inferior two thirds of the en face sagittal image, and is well conserved for normal glenoid geometry. The amount of bone missing is determined by assessing surface area losses from the anteroinferior part of the circle. The reason for the precision of bone loss measurement is that the glenoid bone stock from anterior to posterior is only about 24 to 28 mm and varies from patient to patient. In addition, for approximately each 1.5 to 1.7 mm of glenoid bone loss, this corresponds to a 5% increase in loss of glenoid bone stock. Glenoid bone loss occurs along a line parallel to the long axis of the glenoid (parallel to the 12- to 6-o’clock line). ( Fig. 7 ) Glenoid bone loss greater than 20% to 25% can lead to the glenoid taking on the shape of an inverted pear when viewed arthroscopically from the anterosuperior portal ( Fig. 8 ). Although a Hill-Sachs lesion is present in up to 80% to 100% of patients with anterior instability, it is usually insignificant. However, in patients with glenoid bone loss, it is now well appreciated that a Hill-Sachs lesion can become more significant and engage the glenoid with much less force and anterior translation than those without glenoid bone loss. Thus, one should look at glenoid and humeral head bone loss as a bipolar problem, and make informed decisions regarding treatment based upon the amount of bone loss, patient expectations, and associated recurrent instability risk factors.