Anterior Instability Should Be Treated Arthroscopically—Affirms

Anatomy of Glenohumeral Stability 

The glenohumeral joint is the most mobile joint of the human body. A precise balance must exist between mobility and stability to maintain a functional shoulder. For normal use of the shoulder, it is critical that the humeral head be centralized in the glenoid and coracoacromial arch. Several mechanisms exist to maintain the relatively large humeral head on the shallow and small glenoid.

Stability is provided by the combined influence of static and dynamic structures. The osseous anatomy and articular surfaces, shoulder musculature, and capsuloligamentous complexes all contribute to glenohumeral stability. Version and adhesion–cohesion properties of the articular surface augment stability of the shoulder joint. These properties of the articular surface, however, play a relatively minor role in the pathogenesis of instability. The articulation between the concave glenoid and the humeral head leads to marginal congruency, effectively stabilizing the shoulder joint. As glenoid concavity increases, the inherent stability of the articulation increases by requiring greater displacing forces to cause subluxation or dislocation of the humeral head relative to the glenoid. Glenoid concavity is created by three components: the osseous glenoid, the articular cartilage, and the labrum. Normal development of the glenoid results in a concave structure. The articular cartilage further enhances concavity by having thicker margins around the periphery of the osseous glenoid. The labrum additionally deepens the glenoid concavity and provides a greater surface area for articulation. By increasing the depth, the labrum acts as a “chock block,” preventing the humeral head from sliding or rolling over the glenoid rim.

The shoulder musculature, including the rotator cuff and biceps, contributes significantly to stability. These muscles provide the compressive force across the glenohumeral joint throughout range of motion. The forces of the muscles along with the scapular anatomy lead to concavity compression.1 With the combined compressive forces and concave constraints, higher displacing loads or forces are required to displace the glenohumeral articulation.1, 2 Concavity compression is especially important in the midrange of glenohumeral motion since the capsuloligamentous structures are lax.

The capsuloligamentous structures play a complex role in shoulder stability and supplement the effects of the osseous anatomy and muscular forces. The contribution to stability is highly dependent on the position of the glenohumeral joint. This has been elucidated by multiple biomechanical studies.3, 4 As the glenohumeral joint is abducted, stabilizing function shifts inferiorly in the capsuloligamentous structures.3 The superior glenohumeral ligament plays a critical role in the adducted shoulder. In this position, it restrains inferior translation. The middle glenohumeral ligament resists translation and rotation in the mid- and lower ranges of abduction. The inferior glenohumeral ligament complex acts as the primary restraint to translation when the arm is abducted or externally rotated. In addition to limiting translation, the ligaments prevent excessive humeral rotation at the extremes of motion. With this limitation the musculature is maintained within its optimal working length. When the musculature is stretched beyond its maximal working length, the ligaments experience increased tensile forces, which translate into compressive forces, thus substituting for loss of muscle force contribution.

The capsule also provides this protective effect. The rotator interval between the supraspinatus and subscapularis provides compressive forces where there is no musculature and in the adducted position.5 Studies have shown that addressing the rotator interval increases stability but can lead to decreased range of motion. Gerber and coworkers6 showed that capsular placation of the rotator interval decreased external rotation by 30°. Gartsman and coworkers7 promoted far lateral closure in select cases of instability to avoid restricting external rotation.

Pathoanatomy of Instability 

Historically the classic and essential lesion of glenohumeral instability has been the Bankart lesion. The Bankart lesion corresponds to the detachment of the inferior glenohumeral ligament (IGHL) and labral complex. Neviaser8 noted that the detached labroligamentous complex healed in a medial position on the glenoid neck. This lesion is referred to as the anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion. Being inferior to the equator of the glenoid and its involvement of the IGHL, the ALPSA lesion destabilizes the shoulder, especially when in a position of abduction and external rotation. The ALPSA lesion effectively reduces the “bumper” or chock–block effect of the anterior labrum8, 9 and reduces the concavity–compression of the glenohumeral articulation.1

The current understanding of shoulder instability goes beyond labral injury alone and is multifactorial. Speer and coworkers10 demonstrated that an isolated labral detachment did not lead to instability, but that a Bankart lesion in addition to capsular stretching was sufficient in producing subluxation. Transection of the inferior glenohumeral ligament in cadavera minimally increased anterior translation of the glenohumeral joint.10 Bigliani and coworkers11 found that the IGHL fails in one of three locations: at the glenoid, midsubstance, or humeral insertion. They also demonstrated plastic deformation of the ligament. The findings of stretch injury and redundancy in the capsuloligamentous complex demonstrated the complex nature of instability and the need to address all pathoanatomy leading to instability.

In addition to the soft tissue, pathology there may be osseous lesions leading to instability. Loss of bone stock from the glenoid and/or the humerus (Hill–Sachs lesion) may further destabilize the shoulder articulation. Glenoid erosion alters the anatomy of the articulation by inverting the normal pear-shaped morphology of the glenoid. This leads to a shorter arc of motion by which it can resist loads. Rim fractures essentially decrease the resistance to shear by decreasing rim load. Deficiencies of the humerus may also destabilize the shoulder. Hill–Sachs lesions can either be engaging or nonengaging. Hill–Sachs lesions may engage the anterior glenoid when the long axis of the lesion parallels the glenoid rim.12 On the other hand, when the axis of the lesion lies diagonal to the rim, the lesion is nonengaging. The former is prone to recurrence in arthroscopic repair, while the latter has been treated effectively with arthroscopy.12

Principles of Treatment 

The goal of any treatment is to restore stable functional range of motion of the glenohumeral joint. The detached labrum must be mobilized and repaired to the glenoid rim so that restoration of the stabilizing forces can be achieved. In addition to addressing the labral pathology, associated capsular and/or osseous deficiencies must be dealt with to prevent persistent or recurrent instability. Retensioning of the inferior glenohumeral ligament complex as well as eliminating capsular redundancy or laxity with capsular shifts is critical to the restoration of functional mobility of the shoulder.

Patient selection plays a crucial role in determining whether treatment will be successful. A thorough history and physical examination along with indicated imaging studies is necessary to provide the correct diagnosis and to identify all associated causes of instability. By elucidating the pathoanatomy the surgeon can select an appropriate surgical procedure. Typically, surgical intervention is indicated if mechanical factors such as capsuloligamentous deficiency, muscle imbalance, or glenoid deficiencies are identified since these can be specifically addressed by a targeted procedure.

With a broader knowledge of the pathoanatomy of instability, surgeons have developed modern techniques to address all the pathologic features of instability. Historically open procedures have been the standard of care for the treatment of shoulder instability; however, advancements in arthroscopic surgery have propelled this technique to the forefront of glenohumeral stabilization.

The classic Bankart repair13 or capsular shifts described by Neer have been the traditional approaches in open surgical techniques. With the discovery that labral and capsular lesions are involved in the pathoanatomy of instability and dislocation,10 combination procedures of labral repair and capsular tightening were subsequently utilized. With open procedures, instability can be addressed anatomically or nonanatomically. The aforementioned classic Bankart repair and capsular shifts are included in the anatomic approach. The goal is to restore the normal anatomy of the glenohumeral joint and provide resistance to translation. In the nonanatomic approach, the objective is to create an osseous or soft tissue “checkrein” to glenohumeral translation.

The open technique of Bankart repair13 and capsular tightening has long been considered reliable and effective. It remains an acceptable option today in special circumstances. The advantages of an open technique in the past included direct visualization of labral repair and capsular tightening. Open techniques have been favored over arthroscopic techniques when substantial osseous or capsular deficiencies exist or in irreparable rotator cuff disease. In these special circumstances, grafts or transfers are required to reconstruct the glenoid or capsuloligamentous complexes, which may be possible only with an open and direct technique. Furthermore, open techniques require less technical expertise compared with arthroscopic techniques, thus are favored among many surgeons.

There are disadvantages to open procedures. The major drawback to open techniques is the takedown of the subscapularis to allow visualization (Fig. 1). Reports of subscapularis ruptures or deficiencies have been published and can be devastating to shoulder function. This can lead to functional disability with or without instability. Overtightening of the capsuloligamentous structures is also a concern in open procedures and often occurs when tensioning of the capsule is not performed with the arm in abduction and external rotation. Loss of motion, especially external rotation, after open treatment of shoulder instability may be underreported in the literature but has been noted.14, 15 The reason for this underreporting may be that loss of external rotation was not considered a complication but rather the designed effect of certain procedures.14 The loss of 307 % of external rotation compared with the nonoperative extremity increases the risk of so-called capsulorrhaphy arthropathy.16, 17 Overconstraint of the glenohumeral joint alters normal kinematics, leading to increased joint reactive forces and shear forces.18 Overtensioning of the anterior capsule translates the humeral head posteriorly, causing increased shear on the posterior glenoid. This leads to cartilage erosion and capsulorrhaphy arthropathy.16 Further risks of open procedures include nerve injury, loss of proprioception, and infection.

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Figure 1. (A) Arthroscopic instability repairs are done in a percutaneous fashion without subscapularis takedown and theoretically minimal surgical disruption of capsular proprioception. (B) Open procedures require a larger wound and increased perioperative morbidity. (C) The subscapularis must be tenotomized, or otherwise stripped away from the underlying capsule, potentially affecting proprioceptive function. This tenotomized subscapularis is at risk for disruption in the postoperative period and increases the difficulty of subsequent revisions if necessary. (D) Capsular tenotomy is generally required to perform a shift, in contrast to arthroscopic procedures, which can be performed in situ. (Color version of figure is available online.)

The early short-term studies evaluating open procedures have found low recurrence rates. Rowe and coworkers13 reported a 3.5% recurrence in open procedures. Rowe and coworkers19 later reported that instability recurrence was the most frequently reported complication throughout all procedures. Recent studies, however, have shown higher rates of recurrence than initially reported. Sperber and coworkers20 reported a 12% redislocation rate with open techniques. Athletes were found to have a 23% subluxation or dislocation rate after open techniques.21 Magnusson and colleagues22 found a 17% rate of recurrence in patients treated with open Bankart repairs for posttraumatic recurrent anterior instability. Given this unexpectedly high recurrence rate relative to the classic literature, open procedures should be reconsidered in the treatment of glenohumeral instability.22

Early studies comparing open versus arthroscopic techniques favored the former in addressing instability of the shoulder. Initial reports of arthroscopically treated instability had poor results with failures as high as 50%. These early results may reflect the technique and technology used in the initial arthroscopic procedures at the time of the studies. Labral repairs were usually nonanatomic, and capsular laxity was not addressed.

More recent studies comparing modern techniques have shown equivalency in outcomes between open and arthroscopic techniques. This may be due to the advancements in technology and surgical technique in arthroscopy. Karlsson and coworkers15 looked at 117 patients with symptomatic recurrent anterior posttraumatic instability and a Bankart lesion treated surgically. Patients were either treated arthroscopically with tacks or openly with suture anchors. Although the implants were variable, the recurrence rates (subluxation or dislocation) were comparable. Fifteen percent recurrence was noted in those treated arthroscopically versus 10% recurrence in those with open treatment. Patients treated arthroscopically also had increased external rotation with the arm abducted compared with open treatment (90 versus 80°).

In a comparison of arthroscopic and open procedures in 63 patients with recurrent anterior instability, Cole and Warner9 found no differences in recurrent dislocation, subluxation, or apprehension. The study, however, incorporated a selection process whereby arthroscopic stabilization was reserved for those with anterior translation and a distinct Bankart lesion. If at the time of examination under anesthesia and diagnostic arthroscopy patients had additional inferior translation and capsular laxity, they were allocated to the open procedure. Despite this selection bias, they concluded that both procedures yielded comparable results. They suggested that the best candidates for arthroscopic stabilization were those with instability due to a Bankart lesion without capsuloligamentous laxity.

Looking at more modern techniques, open and arthroscopic procedures appear to be equivalent. Residual instability of 10% both in open and arthroscopic Bankart repairs using suture anchors has been demonstrated.23 In an analysis of modern arthroscopic technique (Bankart lesion repair, labral repair, capsuloligamentous and rotator interval tensioning), Gartsman and coworkers7 reported a 92% good-to-excellent result in 53 patients. Persistent instability was seen in 8% (4/53), one of whom underwent revision surgery.

These studies support the use of arthroscopic technique in shoulder instability. The advantages of arthroscopy include the maintenance of subscapularis integrity, decreased proprioceptive morbidity, decreased neurovascular injury, and better visualization of concomitant pathology (Fig. 1). In addition, surgical times and costs may be decreased; these procedures may often be performed on an outpatient basis. Other speculated advantages include less morbidity and better motion as well as greater success with subsequent revision. The disadvantages of arthroscopic treatment are the required expertise and equipment. The surgeon must have the knowledge of arthroscopic anatomy and technique and be familiar with instrumentation and implants.

As technique and equipment evolves, the indications for arthroscopic repair have also evolved. Current indications include any symptomatic instability without osseous deficiency. Contraindications to arthroscopic approaches include significant osseous deficiency, capsular ruptures or deficiencies requiring grafts, revision procedures, and surgeon inexperience.

Evolution of Arthroscopic Technique 

Arthroscopy of the shoulder has evolved over the past two decades. Arthroscopic repair of the glenohumeral ligaments using metal staples was reported in 1982.24 Because of the high complication rate associated with this technique and the implant, other suture techniques were devised.25 Initial techniques transfixed the labrum to the glenoid neck, essentially creating anterior labroligamentous periosteal sleeve avulsion-type lesions, leading to high failure rates. In addition, capsular laxity was not addressed in the initial techniques.

Morgan and Bodenstab26 developed a transglenoid suture technique that allowed the labrum to be secured at multiple fixation points. The technique also allowed superior and medial shifting of the capsule to provide additional stability. Savoie27 popularized and modified this method. They discovered that the site of attachment was critical and moved the entry point to the glenoid articular surface. The major drawback to this technique was the transscapular drilling. The drilling process was technically demanding and placed the suprascapular nerve at risk. In addition, there was risk for fractures of the glenoid rim due to the stress risers created by drilling.

Speer and coworkers28 introduced the use of single-point transfixation implants to tack down the labrum on the glenoid. These tacks were bioabsorbable and often lead to synovial reaction. Furthermore, capsular laxity could not be addressed with these implantation devices.

Wolf29 pioneered the use of suture anchors in arthroscopic shoulder instability procedures. The use of suture anchors allowed direct repair of the labrum to the glenoid rim without the risks associated with previous techniques. In addition to using suture anchors, Snyder30 applied the use of nonabsorbable sutures to the technique.

With modern suture anchor and suture imbrication techniques, the outcomes of arthroscopic procedures have approached and may exceed the success of traditional open techniques. The indications for arthroscopic treatment are becoming broader as development in technology and technique continues. It is important to realize that the participating surgeons involved in the report literature are specialists and have a greater depth of knowledge of the pathoanatomy of instability and greater expertise in performing certain procedures. The results, thus, may be biased and not uniform. As surgeon experience and training progresses, arthroscopic procedures may become the standard of care in the treatment of shoulder instability.