Arthroscopic Management of Posterior Instability

In comparison with anterior shoulder instability, posterior instability is uncommon, occurring in 2% to 10% of cases, and covering a wide clinical spectrum ranging from locked posterior dislocation to the often subclinical recurrent posterior subluxation (RPS). With increased clinical awareness, imaging advances such as magnetic resonance arthrography, and the development of specific provocative physical examination tests, the identification of RPS in the athletic population is improving. This article describes the anatomic-based arthroscopic approach to treatment of RPS, which allows for enhanced identification and repair of intra-articular pathology including posterior capsular laxity, complete or incomplete detachment of the posterior capsulolabral complex, and inferior capsular tears. While postoperative results are generally good to excellent after stabilization for RPS, there is room for improvement.

In comparison with anterior shoulder instability, posterior instability is uncommon, occurring in 2% to 10% of cases. A posteriorly directed blow to an adducted, internally rotated, and forward-flexed upper extremity is classically described as the sentinel traumatic event. However, recurrent or locked posterior shoulder dislocations from macrotrauma are exceedingly rare in the athletic population. Instead, athletes typically present with posterior shoulder instability secondary to repetitive microtrauma, which can occur in multiple arm positions and under a variety of loading conditions. In 1952, McLaughlin first acknowledged the existence of a wide clinical spectrum of posterior shoulder instability, ranging from locked posterior dislocation to the often subclinical recurrent posterior subluxation (RPS).

In athletics, RPS has been observed in weightlifters, football linemen, golfers, tennis players, butterfly and freestyle swimmers, overhead throwers, and baseball hitters, among others. The origin of RPS is repetitive microtrauma, most commonly leading to posterior capsular attenuation and labral tearing. Regardless of the sport, athletes with RPS typically present with ambiguous complaints of diffuse pain and shoulder fatigue, without distinct injury, often making it challenging to elucidate the underlying pathology and diagnosis.

A thorough history and physical examination, coupled with specific imaging studies, are required to determine the exact pathogenesis of and appropriate treatment options for RPS. With increased clinical awareness, imaging advances such as magnetic resonance arthrography (MRA), and the development of specific provocative physical examination tests, the identification of RPS in the athletic population is improving. Several variables that must be considered during the workup include mechanism of injury (true posterior traumatic dislocation vs repetitive microtrauma vs an acute on chronic subluxation), specific direction of instability (posterior vs posteroinferior or posterosuperior), and the pattern of instability (unidirectional or multidirectional), as these factors will ultimately affect treatment and outcome.

Successful treatment of RPS begins with thorough identification of all of the structural abnormalities present in the affected shoulder, which can include any combination of the labrum, capsule, supporting ligaments, and rotator cuff. Over time, posterior glenohumeral stabilization has evolved from various open procedures to an anatomic-based arthroscopic approach, which allows for enhanced identification and repair of intra-articular pathology including posterior capsular laxity, complete or incomplete detachment of the posterior capsulolabral complex, and inferior capsular tears. While postoperative results are generally good to excellent after stabilization for RPS, there is room for improvement. Accordingly, research continues on both the biomechanical and clinical fronts to further refine diagnostic and treatment approaches to RPS.

Pathoanatomy

The pathogenesis of RPS varies among athletes, in direct relationship to the particular repetitive stresses placed on the posterior structures of the glenohumeral joint during competition and training. For example, activities like push-ups, bench-press weight lifting, and blocking in football linemen all place direct stress on the posterior capsulolabral complex of the shoulder, potentially resulting in RPS. Similarly, the follow-through phase of throwing, pull-through phase in swimming, tennis backhand stroke, and golf backswing can all lead to RPS.

The posterior labrum, capsule, and posterior band of the inferior glenohumeral ligament (IGHL) are the primary stabilizers to posterior translation of the humeral head, particularly between 45° and 90° of glenohumeral abduction. The posterior capsule is delineated by the area between the intra-articular portion of the biceps tendon and the posterior band of the IGHL. The posterior capsule is the thinnest segment of the shoulder capsule, devoid of any supporting ligamentous structures, thus making it prone to attenuation from applied stress. It has been postulated that overhead throwers, tennis players, and swimmers develop shoulder pain associated with progressive laxity of the posterior capsule and fatigue of the static and dynamic stabilizers. Recurrent posterior subluxation can lead to plastic deformation of the posterior capsule, and a patulous posteroinferior capsular pouch with an associated increased joint volume. After a traumatic posterior subluxation or dislocation, athletes may sustain a capsulolabral detachment known as a reverse Bankart tear, further contributing to recurrent instability and symptoms ( Figs. 1 and 2 ).

Many investigators have reported an elaborate role of the anterior IGHL and shoulder capsule in preventing posterior instability, which varies with shoulder position and applied forces. Warren and colleagues studied the static restraints to posterior translation with the arm in the vulnerable position of shoulder flexion and internal rotation. Transection of the infraspinatus, teres minor, and entire posterior capsule was insufficient to produce posterior dislocation; however, when the anterosuperior capsule and superior glenohumeral ligament (SGHL) were transected, a posterior dislocation would develop. This finding led to the development of the “circle concept,” which proposed that dislocation in one direction requires capsular damage on both the same side and the opposite side of the joint. A biomechanical study by Cole and colleagues demonstrated that the rotator interval and SGHL provide static glenohumeral stability by limiting inferior and posterior joint translations with the arm adducted. However, recent work by Provencher and colleagues has demonstrated that rotator interval closure, though associated with a predictable loss of external rotation, has no effect on reducing posterior instability of the glenohumeral joint. Thus, it appears that rotator interval closure is not clinically indicated in the athlete with unidirectional posterior instability, and may actually have a deleterious effect on overhead throwers who rely on functioning in the abduction-external rotation (ABER) position.

Muscular forces from the deltoid and rotator cuff also contribute to the dynamic concavity-compression effect on the humeral head within the glenoid. Of the rotator cuff muscles, the subscapularis provides the most resistance to posterior translation of the shoulder, acting as a dynamic supporter of the action of the posterior band of the IGHL. In one cadaveric study examining the effect of rotator cuff imbalance on the development of labral tear, it was concluded that decreased subscapularis muscle strength in the position simulating the late cocking phase of throwing motion results in increased maximum glenohumeral external rotation and increased glenohumeral contact pressure. It was inferred from these findings that throwers who develop subscapularis fatigue from repetitive throwing may be more susceptible to these forces and a resultant Type II superior labral anterior posterior (SLAP) tear. In their clinical experience with both throwers and nonthrowers, the authors have found that Type II SLAP tears can propagate posteroinferiorly around the glenoid rim, resulting in the Type VIII SLAP tear and symptomatic RPS.

While a full understanding of the pathology contributing to decreased performance in the elite throwing athlete has yet to be established, an evidence-based biomechanical model regarding RPS is taking shape. The humeral head possesses an oblong, or cam, shape due to the presence of the greater and lesser tuberosities. In the ABER position, the anterior band of the IGHL becomes taut as it is draped over the anteroinferior aspect of the eccentrically positioned humeral head, providing a check-rein against excessive external rotation in that position. In pitchers, increased glenohumeral external rotation is favored at the expense of internal rotation in an effort to prime the late cocking phase of throwing, primarily because an enhanced late cocking phase leads to more rapid internal humeral rotation in follow-through and increased pitch velocity. Chronic use of the shoulder in this manner, with external rotation priming, ultimately results in a glenohumeral internal rotation deficit (GIRD), which manifests structurally as a posterior capsular contracture.

Burkhart and colleagues have postulated that the cam effect of the humerus is overcome by the thrower, who by developing a posterior capsular contracture shifts the rotational fulcrum posterosuperiorly; this shift of the rotational fulcrum allows the humeral head to clear the anteroinferior labroligamentous restraints and achieve more external rotation in abduction. With this adaptation, it is felt that the posterior and posterosuperior glenohumeral restraints in overhead throwers are susceptible to repetitive microtrauma events during the follow-through phase with the shoulder in the adducted, flexed, and internally rotated position. Throwers who have GIRD are thought to experience repetitive microtrauma after ball release, resulting in progressive tearing of the superior, and potentially posterior labrum ( Fig. 3 ).

The resultant posteroinferior capsular thickening from contracture associated with GIRD has been visualized on magnetic resonance (MR) examinations of the throwing athlete. In addition, throwing athletes who have painful posterior shoulder instability and commonly perform with the shoulder in the ABER position have been found on dynamic MRA to undergo a phenomenon described as posterosuperior labral “peel back.” During the “peel back” event, when the arm is placed in the ABER position during MRA, the detached posterosuperior labral tissue is seen separating from and moving medially to the glenoid rim. This dynamic phenomenon can also be visualized arthroscopically with the arm in the ABER position.

Not all throwing athletes demonstrate concurrent findings of GIRD and posterior labral tear, highlighting the complexity of the pathogenesis of RPS in this population. It has been observed that some adaptive changes can occur in the throwing shoulder without negative consequence, while other athletes reach a tipping point that may lead to symptoms. After approximately 25° of GIRD, the posterosuperior shift in the glenohumeral center of rotation ceases to be adaptive and instead leads to pathologic shearing forces on the posterosuperior labrum and rotator cuff. In effect, the excessive external rotation in the ABER position exposes the posterosuperior labrum, long head of the biceps tendon, and undersurface rotator cuff tendons to large rotatory lever arm forces, resulting in the “peel back” phenomenon. In addition, the posterosuperior shift of the humeral head in the ABER position has been found to result in a relative redundancy of the anteroinferior capsuloligamentous complex. This redundancy in the anteroinferior shoulder capsule is caused by a decrease in the cam effect of the proximal humerus, and may have clinical implications in the pathophysiology of the disabled throwing shoulder.

The clinical presentation of a posterosuperior labral tear in combination with posteroinferior capsular contracture in throwing athletes differs from the spectrum of pathology seen in offensive linemen, weightlifters, and those athletes who are frequently subjected to repetitive high loads with the arm in the forward flexed and adducted position. In the latter, these high shearing forces on the posterior labrum result in labral tearing, posterior capsular laxity, and capsular redundancy. This condition is best treated with arthroscopic posterior labral repair and additional posterior capsular plication as indicated. On the contrary, when GIRD and RPS are present in the overhead thrower, stretching of the posteroinferior capsular contracture by way of “sleeper stretches” is a more appropriate initial treatment. In addition, subscapularis muscle strengthening may play a role. Ultimately, arthroscopic posterior labral repair with optional posterior capsular release can be performed to treat recalcitrant symptoms in the thrower with GIRD and RPS. In these cases, the GIRD is typically successfully treated preoperatively with stretching, and the associated capsulolabral avulsion is treated with arthroscopic repair; in rare cases of recalcitrant GIRD a limited capsular release is concomitantly performed during surgery.

Of additional importance is the identification and treatment of scapular dyskinesia, which has variable clinical implications. Scapular winging can act as a compensatory mechanism to prevent posterior subluxation of the humeral head in some patients, although in other patients scapular winging is thought to be the primary cause of subluxation. In a recent study of 8 elite golfers with posterior shoulder instability, fatigue developed in the serratus anterior muscle during competitive play, possibly contributing to scapulothoracic asynchrony and the combination of posterior shoulder instability and subacromial impingement. Further study of the relationship between scapular mechanics and shoulder stability is warranted. Typically a periscapular muscle strengthening program is incorporated into the physical therapy protocol for RPS to account for the possible contribution of scapular dyskinesia.

Finally, in baseball hitters “batter’s shoulder” has recently been described by Dines and colleagues as a cause of RPS. This syndrome affects the lead shoulder during a baseball swing, as dynamic posterior pulling forces approach 500 N, resulting in posterior labral tearing. Typically the nondominant arm is affected, resulting in pain with batting. It has been inferred that golfers may suffer from a similar mechanism of injury. Of note, arthroscopic posterior labral repair (n = 9) or labral debridement (n = 2) was reported to allow return to previous level of batting in 10 of 11 patients with this condition.

History and physical examination

Thorough knowledge of an athlete’s sport, position, and training regimen is critical in deducing the pathogenesis and specific pathology associated with RPS. Pollock and Bigliani noted that two-thirds of athletes who ultimately required surgery presented with complaints of difficulty using the shoulder outside of sports, particularly with the arm above the horizontal. An inquiry should also be made regarding mechanical symptoms, as one study found that 90% of patients with symptomatic RPS noted clicking or crepitation with motion. Often this crepitus can be reproduced during examination, and is caused by discrete posterior capsulolabral pathology.

Physical examination of a shoulder suspected of RPS begins with inspection, focusing on asymmetry, scapular dysrhythmia, and muscular atrophy. A skin dimple over the posteromedial deltoid of both shoulders has been found to be 62% sensitive and 92% specific in correlating with posterior instability. Tenderness to palpation as a result of inflammation is next assessed at the posterior glenohumeral joint line, greater tuberosity, and biceps tendon. Patients with posterior instability have been found to have posterior joint line tenderness, likely caused by posterior synovitis or posterior rotator cuff tendinosis secondary to multiple episodes of instability.

Range of motion (ROM) of both shoulders is assessed in forward elevation, abduction in the scapular plane, external rotation with the arm at the side, and internal rotation behind the back to the highest vertebral level. With the patient supine, the arm is abducted 90°, the scapula stabilized, and internal and external glenohumeral rotation measured. These supine measurements are compared with the contralateral shoulder and are used to calculate total arc of rotation (total external rotation plus total internal rotation) and GIRD (side-to-side difference in internal rotation).

Strength testing is performed bilaterally, with a focus on the rotator cuff musculature, and graded on a typical 5-point scale. The majority of athletes with RPS who are tested have Grade 4 or Grade 5 strength. Supraspinatus strength is tested with a downward force while the arm is abducted 90° in the scapular plane. Infraspinatus and teres minor strength are assessed with resisted external rotation, with the arm adducted and elbow flexed 90°. Subtle weakness can be detected in side-to-side comparison if the posterior rotator cuff has damage. Lastly, subscapularis strength is tested with the lumbar lift-off and belly press tests.

Glenohumeral stability is assessed on both shoulders with the patient supine. The load and shift maneuver is performed with the arm held in 60° of abduction and neutral rotation. In this position, a moderate axial load is applied to the glenohumeral joint in combination first with an anterior force in an attempt to translate the humeral head over the anterior glenoid rim. The test is repeated with a posterior directed force ( Fig. 4 ). Anterior and posterior laxity is quantified as 0 for a humeral head that does not translate to the glenoid rim, 1+ for a humeral head that translates to but does not translate over the glenoid rim, 2+ for a humeral head that translates over the glenoid rim but spontaneously reduces, and 3+ for a humeral head that translates over the glenoid rim and does not spontaneously reduce.

To assess for excessive IGHL and SGHL laxity, a “sulcus” test is performed by applying longitudinal traction with the arm adducted and in neutral rotation, with the patient seated. The test is repeated in 30° of external rotation. Laxity is quantified as 1+ for an acromiohumeral distance less than 1 cm, 2+ for an acromiohumeral distance between 1 and 2 cm, or 3+ for an acromiohumeral distance greater than 2 cm. A 3+ “sulcus sign” that remains 2+ or greater in 30° of external rotation is considered pathognomonic for an incompetent rotator interval.

Generalized ligamentous laxity may also contribute to multidirectional instability (MDI) and thus should be graded on the 9-point Beighton Scale with the following tests: (1) ability to hyperextend the elbows (1 point for each extremity), (2) ability to passively touch the thumb to the adjacent forearm with the wrist in flexion (1 point for each extremity), (3) ability to passively hyperextend the small finger metacarpophalangeal joint more than 90° (1 point for each extremity), (4) ability to hyperextend the knees (1 point for each extremity), and (5) ability to touch the palms to the floor with feet together (1 point). Patients who score 5 points or greater on the Beighton Scale are considered ligamentously lax.

Several specialized tests have been devised to further elucidate capsulolabral pathology in the shoulder. The Jerk Test is used to assess to assess posterior stability in the seated position. The medial border of the scapula is stabilized with one hand, and the other hand applies a posteriorly directed force to the 90° forward flexed, adducted, and internally rotated arm. The test is positive if posterior subluxation or dislocation of the humeral head occurs while simultaneously reproducing the symptoms of pain and apprehension.

The Kim Test can also aid in the diagnosis of posterior and posteroinferior shoulder instability. The patient is seated and the arm is placed in 90° of abduction in the scapular plane, and an axial load is applied. The arm is subsequently forward elevated an additional 45°, and a posteroinferior vector is placed on the glenohumeral joint. Kim and colleagues concluded that the test is positive with a sudden onset of posterior subluxation with pain. This test, in combination with the Jerk Test, was found to be 97% sensitive in detecting a posteroinferior labral lesion. The investigators also found that patients who experienced pain with the Kim Test were more likely to require operative intervention to alleviate their symptoms than those who did not experience pain.

The Circumduction Test is particularly useful in higher grades of chronic posterior instability, and is performed with the patient seated. With the elbow in full extension, the arm is brought into 90° of forward elevation and slight adduction. Similar to the Jerk Test, a posteriorly directed load is applied, which subluxates, or possibly dislocates, the humeral head posteriorly. The arm is then circumducted with a combination of abduction and extension until the head reduces into the glenoid. A positive test is a palpable, and typically audible, clunk as the posteriorly subluxated head reduces into the glenoid. In patients with chronic posterior instability, this test can often be performed without pain or muscle guarding.

In some cases of RPS, particularly involving overhead throwers, a posterior labral tear is associated with a superior labral tear, resulting in the Type VIII SLAP tear. Accordingly, when examining a shoulder suspected of RPS, the Active-Compression Test for superior labral pathology should also be performed. For this test, the patient is seated and the arm is forward elevated 90°, adducted 10°, and internally rotated with the elbow in full extension. A downward force is placed on the arm. A positive test is confirmed when pain is described as “deep,” and the pain is eliminated or decreased when the maneuver is repeated with the arm in external rotation.

Impingement signs may also be positive in patients with RPS, and should be sought during physical examination. It is believed that the stress-related changes that can occur in the posterior rotator cuff can manifest as a secondary impingement syndrome in some cases.

History and physical examination

Thorough knowledge of an athlete’s sport, position, and training regimen is critical in deducing the pathogenesis and specific pathology associated with RPS. Pollock and Bigliani noted that two-thirds of athletes who ultimately required surgery presented with complaints of difficulty using the shoulder outside of sports, particularly with the arm above the horizontal. An inquiry should also be made regarding mechanical symptoms, as one study found that 90% of patients with symptomatic RPS noted clicking or crepitation with motion. Often this crepitus can be reproduced during examination, and is caused by discrete posterior capsulolabral pathology.

Physical examination of a shoulder suspected of RPS begins with inspection, focusing on asymmetry, scapular dysrhythmia, and muscular atrophy. A skin dimple over the posteromedial deltoid of both shoulders has been found to be 62% sensitive and 92% specific in correlating with posterior instability. Tenderness to palpation as a result of inflammation is next assessed at the posterior glenohumeral joint line, greater tuberosity, and biceps tendon. Patients with posterior instability have been found to have posterior joint line tenderness, likely caused by posterior synovitis or posterior rotator cuff tendinosis secondary to multiple episodes of instability.

Range of motion (ROM) of both shoulders is assessed in forward elevation, abduction in the scapular plane, external rotation with the arm at the side, and internal rotation behind the back to the highest vertebral level. With the patient supine, the arm is abducted 90°, the scapula stabilized, and internal and external glenohumeral rotation measured. These supine measurements are compared with the contralateral shoulder and are used to calculate total arc of rotation (total external rotation plus total internal rotation) and GIRD (side-to-side difference in internal rotation).

Strength testing is performed bilaterally, with a focus on the rotator cuff musculature, and graded on a typical 5-point scale. The majority of athletes with RPS who are tested have Grade 4 or Grade 5 strength. Supraspinatus strength is tested with a downward force while the arm is abducted 90° in the scapular plane. Infraspinatus and teres minor strength are assessed with resisted external rotation, with the arm adducted and elbow flexed 90°. Subtle weakness can be detected in side-to-side comparison if the posterior rotator cuff has damage. Lastly, subscapularis strength is tested with the lumbar lift-off and belly press tests.

Glenohumeral stability is assessed on both shoulders with the patient supine. The load and shift maneuver is performed with the arm held in 60° of abduction and neutral rotation. In this position, a moderate axial load is applied to the glenohumeral joint in combination first with an anterior force in an attempt to translate the humeral head over the anterior glenoid rim. The test is repeated with a posterior directed force ( Fig. 4 ). Anterior and posterior laxity is quantified as 0 for a humeral head that does not translate to the glenoid rim, 1+ for a humeral head that translates to but does not translate over the glenoid rim, 2+ for a humeral head that translates over the glenoid rim but spontaneously reduces, and 3+ for a humeral head that translates over the glenoid rim and does not spontaneously reduce.

To assess for excessive IGHL and SGHL laxity, a “sulcus” test is performed by applying longitudinal traction with the arm adducted and in neutral rotation, with the patient seated. The test is repeated in 30° of external rotation. Laxity is quantified as 1+ for an acromiohumeral distance less than 1 cm, 2+ for an acromiohumeral distance between 1 and 2 cm, or 3+ for an acromiohumeral distance greater than 2 cm. A 3+ “sulcus sign” that remains 2+ or greater in 30° of external rotation is considered pathognomonic for an incompetent rotator interval.

Generalized ligamentous laxity may also contribute to multidirectional instability (MDI) and thus should be graded on the 9-point Beighton Scale with the following tests: (1) ability to hyperextend the elbows (1 point for each extremity), (2) ability to passively touch the thumb to the adjacent forearm with the wrist in flexion (1 point for each extremity), (3) ability to passively hyperextend the small finger metacarpophalangeal joint more than 90° (1 point for each extremity), (4) ability to hyperextend the knees (1 point for each extremity), and (5) ability to touch the palms to the floor with feet together (1 point). Patients who score 5 points or greater on the Beighton Scale are considered ligamentously lax.

Several specialized tests have been devised to further elucidate capsulolabral pathology in the shoulder. The Jerk Test is used to assess to assess posterior stability in the seated position. The medial border of the scapula is stabilized with one hand, and the other hand applies a posteriorly directed force to the 90° forward flexed, adducted, and internally rotated arm. The test is positive if posterior subluxation or dislocation of the humeral head occurs while simultaneously reproducing the symptoms of pain and apprehension.

The Kim Test can also aid in the diagnosis of posterior and posteroinferior shoulder instability. The patient is seated and the arm is placed in 90° of abduction in the scapular plane, and an axial load is applied. The arm is subsequently forward elevated an additional 45°, and a posteroinferior vector is placed on the glenohumeral joint. Kim and colleagues concluded that the test is positive with a sudden onset of posterior subluxation with pain. This test, in combination with the Jerk Test, was found to be 97% sensitive in detecting a posteroinferior labral lesion. The investigators also found that patients who experienced pain with the Kim Test were more likely to require operative intervention to alleviate their symptoms than those who did not experience pain.

The Circumduction Test is particularly useful in higher grades of chronic posterior instability, and is performed with the patient seated. With the elbow in full extension, the arm is brought into 90° of forward elevation and slight adduction. Similar to the Jerk Test, a posteriorly directed load is applied, which subluxates, or possibly dislocates, the humeral head posteriorly. The arm is then circumducted with a combination of abduction and extension until the head reduces into the glenoid. A positive test is a palpable, and typically audible, clunk as the posteriorly subluxated head reduces into the glenoid. In patients with chronic posterior instability, this test can often be performed without pain or muscle guarding.

In some cases of RPS, particularly involving overhead throwers, a posterior labral tear is associated with a superior labral tear, resulting in the Type VIII SLAP tear. Accordingly, when examining a shoulder suspected of RPS, the Active-Compression Test for superior labral pathology should also be performed. For this test, the patient is seated and the arm is forward elevated 90°, adducted 10°, and internally rotated with the elbow in full extension. A downward force is placed on the arm. A positive test is confirmed when pain is described as “deep,” and the pain is eliminated or decreased when the maneuver is repeated with the arm in external rotation.

Impingement signs may also be positive in patients with RPS, and should be sought during physical examination. It is believed that the stress-related changes that can occur in the posterior rotator cuff can manifest as a secondary impingement syndrome in some cases.

Imaging

Three radiographs of the shoulder are routinely obtained for the workup of RPS: (1) an anteroposterior view in the plane of the scapula, (2) an axillary view, and (3) a scapular Y lateral view. In most patients with RPS radiographic images are normal, although in some cases a posterior glenoid lesion or impaction of anterior humeral head (Reverse Hill-Sachs lesion) can be visualized. In rare instances, a fracture of the lesser tuberosity will give evidence of a previous posterior dislocation. In addition, the West Point radiographic view can be useful for detecting fractures of the glenoid rim or subtle ectopic bone formation around the glenoid.

MRA is the most sensitive diagnostic test for identifying lesions of the posterior labrum and capsule. Specific MRA findings indicative of posterior shoulder instability include posterior translation of the humeral head relative to the glenoid, posterior labrocapsular avulsion, posterior labral tear or splitting, discrete posterior capsular tears or rents, reverse humeral avulsion of the glenohumeral ligaments (HAGL), posterior labrum periosteal sleeve avulsion (POLPSA), and subscapularis tendon avulsion ( Fig. 5 ). The Kim classification is used to specifically describe posterior labral tear morphology: Type I, incomplete detachment; Type II (the “Kim lesion”), a concealed complete detachment; Type III, chondrolabral erosion; and Type IV, flap tear of the posteroinferior labrum ( Figs. 6–8 ). The Kim lesion appears arthroscopically as a crack at the junction of the posteroinferior glenoid articular cartilage and labrum, through which a complete detachment of the deeper labrum from the glenoid rim can be identified (see Fig. 7 ).