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Posterior shoulder stabilisation

72 citationsUpdated Sep 2026

For patients: a plain-language version of this topic is available. See the patient guide.

Overview

Arthroscopic stabilization for posterior shoulder instability demonstrates good outcomes, characterized by high patient satisfaction and low rates of recurrent instability, revisions, and residual pain [17]. Early and midterm results are promising [6], with a successful track record and a minimal complication profile [9]. Patients with symptomatic posterior instability benefit from arthroscopic stabilization regardless of the radiologist interpretation of the magnetic resonance arthrogram [26]. Return to sport is common, occurring between 4.3 and 8.6 months post-surgery [25]. While soft-tissue stabilization alone may be insufficient in patients with substantial bone loss to the posterior glenoid and/or the anterior humeral head [4], successful correction of scapular anatomy can improve static subluxation and restore subjective and objective shoulder stability at a minimum of 2 years [5].

Failure of primary shoulder stabilization procedures is often related to uncorrected anatomic pathology, and the instability severity index score permits precise identification of patients at risk [21]. Persistence or recurrence of static/dynamic posterior instability after correction of glenoid version alone may be related to incomplete restoration of the intrinsic stability conferred by normal acromial anatomy [13]. Coracoid morphology differs significantly in patients undergoing posterior shoulder stabilization compared to those undergoing surgery for anterior instability or a comparison cohort [23]. The thresholds defined in the 2025 study provide a guideline for interpreting patient outcomes following arthroscopic stabilization, allowing for earlier detection of recurrent posterior instability [3].

Surgical positioning and technique variations are active areas of investigation. Additional long-term randomized trials comparing beach-chair and lateral decubitus positions are needed to better understand the potential advantages and disadvantages of surgical positioning [1]. The beach-chair position technique maintains the principles of anatomic restoration and reliable fixation while expanding the practical applicability of this position for posterior shoulder instability [18]. A single-portal arthroscopic posterior capsulorrhaphy technique offers an efficient, reproducible procedure to address posterior shoulder instability pathology [19], and the "pinch-and-tuck" arthroscopic technique is an alternative method for capsular plication that effectively and safely addresses capsular laxity [32]. Further research is necessary to define the clinical outcomes in revision posterior stabilization due to significant heterogeneity in the clinical outcomes reported to date [29].

Anatomy & Pathophysiology

Bony Anatomy

The scapula, together with the clavicle, constitutes the shoulder girdle [71]. The scapula spans the second through seventh ribs and serves as an attachment for 17 muscles [83]. It is attached to the axial skeleton by the acromioclavicular (AC) and sternoclavicular (SC) joints [71]. The scapula is separated from the chest wall by thin gliding fibro-fatty tissue, allowing its smooth excursion over the chest wall [71]. The scapula is anteverted on the chest wall approximately 30 degrees relative to the body [83]. The scapular spine is an osseous ridge that separates the supraspinatus and infraspinatus fossae [72]. The lateral pillar connects the inferior border of the glenoid with the inferior angle of the scapula, while the spinal pillar arises from the central part of the glenoid and continues medially to become part of the base of the scapular spine [71]. The weakest bone in the scapula is located primarily in the central part of the biomechanical body, specifically in the infraspinous fossa, and the weakest area of the circumference of the biomechanical body is the spinomedial angle [71].

The glenoid is a convex structure of shallow depth shaped like an inverted pear [69]. The glenoid cavity is a shallow socket, approximately one third the size of the humeral head [70]. The glenoid averages 5° of retroversion in relation to the axis of the scapular body [72], with a range from 2 degrees of anteversion to 7 degrees of retroversion [81]. The glenoid is retroverted approximately 5 degrees relative to the scapular body [83]. The glenoid inclination averages 4.2 degrees (–7 to 20 degrees) [81]. The subchondral bone of the glenoid is relatively flat, with the articular concavity augmented by cartilage and a circumferential labrum [72]. The glenoid articular surface radius of curvature is 2 to 3 mm larger than that of the humeral head [81]. The glenoid radius of curvature is 22-28 mm [81]. The glenoid diameter superior anteroposterior is 18-30 mm, and the inferior anteroposterior diameter is 21-35 mm [81]. The glenoid superoinferior height is 30-48 mm [81]. The glenoid surface area is 4-6 mm, and the glenoid cartilage thickness is 2.16 mm [81].

The humeral head is retroverted an average of 30 degrees [70], or 30 degrees relative to the transepicondylar axis of the humerus [83]. Proximal humeral retroversion is highly variable, ranging from 0 to 55 degrees, depending on the method used for measurement [81]. The humeral head averages 19° of retroversion and 41° of inclination (neck-shaft angle) [72]. The average neck-shaft angle is 45 degrees (±5 degrees), with a range of 30 to 50 degrees [81], while another source cites an average of 135 degrees [70]. The head-shaft angle is 30-55 degrees [81]. The humeral head inclination is 30-55 degrees [81]. The articular surface of the humeral head is essentially spherical, with an arc of approximately 160 degrees covered by articular cartilage [81]. The radius of curvature of the humeral head is approximately 25 mm and is slightly larger in men than in women [81], with a range of 23-28 mm [81]. The humeral head surface area is 11-19 mm, and the humeral head cartilage thickness is 1.44 mm [81]. The superior margin of the humeral head articular surface normally is superior to the top of the greater tuberosity by 8 to 10 mm [81].

The glenoid articular surface and the labrum combine to create a socket that is approximately 9 mm deep in the superoinferior direction and 5 mm deep in the anteroposterior direction [82]. Adding the glenoid labrum increases the glenoid surface to 75% of the humeral head vertically and 57% horizontally [82]. The bony anatomy contributes little to stability and has been compared with a golf ball on a tee [82]. The distance from the lateral base of the coracoid process to the lateral margin of the greater tuberosity is called the lateral humeral offset [81]. A significant decrease in lateral humeral offset reduces the lever arms for the deltoid and supraspinatus muscles, which weakens abduction and impairs function, while a significant increase causes excessive tension on the soft tissues ("overstuffing" of the joint), resulting in loss of motion and likely accelerating polyethylene wear [81]. Humeral articular malposition of more than 4 mm led to increased subacromial contact, and offset of 8 mm in any direction significantly decreased passive range of motion [81]. Anatomic reconstruction of the humeral head/humeral shaft offset should be within 4 mm of normal to minimize subacromial contact and maximize glenohumeral motion [81]. The medial (coronal) humeral offset is 4-14 mm, and the posterior (transverse) humeral offset is –2 to 10 mm [81].

The acromion has three ossification centers: the metacromion (base), the mesoacromion (middle), and the preacromion (tip) [72]. Failure of fusion of acromial ossification centers results in os acromiale [72]. The relationship between acromial anatomy and rotator cuff disease remains controversial, and the classification of acromial morphology (flat, curved, or hooked) is challenged by poor interobserver reliability [72]. The relationship between coracoid morphology and subscapularis tears is controversial [72]. The coracobrachialis muscle and the short head of the biceps tendon originate from the coracoid process, while the pectoralis minor muscle inserts onto the medial coracoid process [72].

The proximal humerus contains the humeral head, lesser and greater tuberosities, bicipital groove, and proximal humeral shaft [70]. The anatomic neck lies at the junction of the head and the tuberosities, and the surgical neck lies below the greater and lesser tuberosities [70]. The greater tuberosity provides attachment for the supraspinatus, infraspinatus, and teres minor muscles, while the lesser tuberosity contains the attachment of the subscapularis muscle [70]. Within the bicipital groove lies the biceps tendon, which is covered by the transverse humeral ligament [70]. The humeral shaft extends from the level of the insertion of the pectoralis major muscle proximally to the supracondylar ridge distally [70]. The upper portion of the humeral shaft is cylindrical and then becomes more flattened in an anteroposterior direction as it proceeds distally [70]. Medial and lateral intermuscular septae divide the arm into anterior and posterior compartments [70]. In the anterior compartment reside the biceps brachii, coracobrachialis, and brachialis muscles, along with the neurovascular bundle coursing along the medial border of the biceps with the brachial artery and vein and the median, musculocutaneous, and ulnar nerves [70]. In the posterior compartment reside the triceps brachii muscle and the radial nerve [70].

The proximal humerus has three centers of ossification: the humeral head (4 to 6 months), the greater tuberosity (1 to 3 years), and the lesser tuberosity (3 to 5 years) [72]. The proximal humeral ossification centers fuse to the shaft at age 17 to 20 years [72]. The clavicle is the first bone to ossify (fifth week of gestation) and is the only long bone to ossify by intramembranous ossification [72]. The medial (sternal) epiphysis of the clavicle is the last ossification center to fuse, at age 20 to 25 years [72]. The scapular body ossification begins at the eighth week of gestation [72].

Ligamentous & Soft Tissue Anatomy

The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch, a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [69]. The superior shoulder suspensory complex (SSSC) provides a stable connection between the scapula and the axial skeleton [72]. The SSSC is composed of the glenoid, the coracoid process, the coracoclavicular ligaments, the distal clavicle, the AC joint, and the acromion [72]. The superior strut of the SSSC comprises the middle clavicle, and the inferior strut comprises the lateral scapular border/spine of the scapula [72].

The glenoid labrum provides concavity and up to 50% of marginal glenoid socket depth [72]. The glenoid is encircled by the labrum, composed of dense fibrocartilaginous tissue, which increases the depth of the socket by 50% around the humeral head [82]. The rotator interval is defined medially by the base of the coracoid, superiorly by the supraspinatus tendon, and inferiorly by the subscapularis tendon [72]. The rotator interval contains the coracohumeral (CH) ligament, the superior glenohumeral ligament (SGHL), and the intra-articular portion of the long head of the biceps tendon [72]. Laxity of the rotator interval results in inferior laxity (the sulcus sign), while contracture of the rotator interval is seen with adhesive capsulitis [72].

The CH ligament restricts external rotation in adduction and is a static restraint to inferior and posterior translation in adduction and external rotation [72]. The SGHL is a primary static restraint against anterior translation with the arm at the side [72]. With the CH ligament, the SGHL forms a pulley that provides restraint against medial subluxation of the long head of the biceps tendon [72]. The middle glenohumeral ligament (MGHL) is a primary static restraint against anterior translation with the arm in external rotation and 45° of abduction [72]. The anterior band of the inferior glenohumeral ligament (AB-IGHL) is a primary static restraint against anterior-inferior dislocation of the glenohumeral joint in 90° of abduction and external rotation (position of apprehension) [72]. The posterior band of the IGHL (PB-IGHL) is a primary static restraint against posterior-inferior translation in internal rotation and adduction [72].

The rotator cuff consists of four muscles: the subscapularis, supraspinatus, infraspinatus, and teres minor muscles [70]. The teres major is not a rotator cuff muscle [70]. The cuff muscles serve as depressors of the humeral head to allow the deltoid to efficiently abduct the humerus [70]. The infraspinatus and teres minor are external rotators, while the subscapularis is an internal rotator of the humerus [70]. The deltoid and pectoralis major muscles, along with the rotator cuff, cause predictable displacement of fractures around the proximal humerus [70].

The scapula has only one true diarthrodial articulation, the acromioclavicular (AC) joint [72]. The AC joint is a small diarthrodial joint with an interposed fibrocartilaginous disk [72]. The superior and posterior AC ligaments are the primary stabilizers to anterior and posterior (horizontal) translation of the clavicle [72]. The sternoclavicular (SC) joint is the only true diarthrodial articulation between the upper appendicular and axial skeletons [72]. The posterior SC joint capsule and ligaments are the primary stabilizers to anterior and posterior translation of the medial clavicle [72]. The coracoclavicular ligaments (conoid: medial; trapezoid: lateral) are the primary stabilizers to superior (vertical) translation of the distal clavicle [72].

Vascular & Neural Anatomy

The proximal humerus receives its blood supply from the anterior and posterior humeral circumflex branches from the third division of the axillary artery [69]. The anterior humeral circumflex artery provides vascular inflow to the humeral head by way of its terminal anterolateral branch known as the artery of Laing (arcuate artery) [69]. The anterolateral ascending branch of the anterior humeral circumflex artery provides the primary blood supply to the humeral head [72]. The terminal intraosseous portion of the anterior humeral circumflex artery enters at the proximal aspect of the intertubercular groove as the arcuate artery [72]. The major blood supply to the humeral head is through the ascending branch of the anterior humeral circumflex artery, which penetrates the head at the bicipital groove and becomes the arcuate artery [70]. The posterior humeral circumflex artery travels with the axillary nerve, enters the quadrilateral space posteriorly, and anastomoses with a branch of the anterior circumflex to supply the posterior cuff [69].

The primary blood supply to the clavicle is periosteal; no nutrient artery is present [72]. Important structures that lie in the vicinity of the shoulder joint include the brachial plexus and axillary artery, which are anterior to the coracoid process of the scapula and humeral head [70]. Nerves innervating muscles around the shoulder include the axillary, suprascapular, subscapular, and musculocutaneous nerves [70]. The superior transverse scapular ligament arises from the medial base of the coracoid overlying the suprascapular notch [72]. The suprascapular artery runs superior to the superior transverse scapular ligament, while the suprascapular nerve runs deep to it [72]. Entrapment of the suprascapular nerve at the superior transverse scapular ligament causes denervation of both the supraspinatus and the infraspinatus [72]. The spinoglenoid ligament overlies the suprascapular nerve at the spinoglenoid notch [72]. Entrapment, traction, or compression of the suprascapular nerve at the spinoglenoid notch causes denervation of the infraspinatus [72].

Kinematics & Biomechanics

Normal shoulder motion is approximately two-thirds glenohumeral and one third scapulothoracic [72]. The scapula serves for attachment of a number of muscles originating from the axial skeleton that control its motion [71]. Thanks to its relatively free connection with the axial skeleton, the scapula is [71]. Stability of the glenohumeral joint depends on capsule, ligament, and muscle [70]. A redundant capsule allows for motion [70].

Fractures of the anatomic neck have a poor prognosis because of complete disruption of the blood supply to the head [70]. Surgical neck fractures are common, and with these, the blood supply to the head is preserved [70]. The brachial plexus and axillary artery can also be injured with anterior shoulder dislocations [70]. The radial nerve is commonly injured in humeral shaft fractures, particularly at the junction of the middle and distal third (Holstein-Lewis fracture) [70]. An axillary nerve injury from proximal humeral fracture or fracture-dislocation would result in paralysis of the deltoid muscle and anesthesia over the “badge” region at the lateral proximal arm [70].

Classification

ABC Classification: This system categorizes posterior shoulder instability (PSI) into three groups based on the nature of the pathology: Type A (first-time), Type B (dynamic), and Type C (static) [34]. Type B is further subdivided into functional (B1) and structural (B2) dynamic instability [34]. Type B1 dynamic instability is defined by a pattern where instability results from pathological activation of the rotator cuff and periscapular muscles [16]. In this context, the pectoralis major stabilizes the glenohumeral joint by resisting superior migration of the humeral head and enhancing scapulothoracic stabilization of the latissimus dorsi and deltoid muscles [16]. Dysfunction of the pectoralis major may compromise glenohumeral stability [16]. Historically, the absence of structural pathology on diagnostic imaging for dynamic-functional instability led to the dismissal of this subtype as attention-seeking or psychiatric behavior [16]. Surgical stabilization is generally not recommended for dynamic-functional instability, as it is associated with poor outcomes [16]. The current gold standard for dynamic-functional instability focuses on normalizing the pathological muscle activation pattern [16].

Other Considerations: Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays [8]. In a study of shoulder dislocations, posterior dislocations occurred in 2% of patients, while anterior dislocations occurred in 98% [48]. Dislocations are grouped as atraumatic and traumatic; atraumatic dislocations are characterized by mild variation in the shape of the humeral head and variation in the size and depth of the glenoid fossa [48]. Patients with atraumatic dislocations were noted frequently to have hyperflexible joints and relatively poor supporting muscles of the shoulder joint [48]. The incidence of recurrence for atraumatic dislocations was 86%, compared to 57% for traumatic dislocations [48]. Seizures were most commonly implicated in the aetiology of posterior shoulder dislocations [61]. Female patients were significantly more likely to have posterior shoulder instability, while male patients were significantly more likely to have anterior shoulder instability [22]. Coracoid morphology differs significantly in patients undergoing posterior shoulder stabilization when compared to patients undergoing surgery for anterior instability or a comparison cohort [23]. Posterior stability of the shoulder depends on acromial anatomy, and persistence or recurrence of static/dynamic posterior instability after correction of glenoid version alone may be related to incomplete restoration of the intrinsic stability conferred by normal acromial anatomy [13].

Clinical Presentation

History and Mechanism

Recurrent posterior shoulder instability is an uncommon condition that is often unrecognized, leading to incorrect diagnoses and delays [8]. Female patients are significantly more likely to present with posterior shoulder instability compared to male patients [22]. In classic posterior instability, patients typically report no identifiable mechanism of injury, with pain serving as the primary symptom [49]. Microtraumatic posterior shoulder instability is characterized by symptomatic posterior translation of the glenohumeral joint, commonly resulting from a gradual overload of glenohumeral joint structures [33].

In traumatic posterior dislocation, the history must define the mechanism of injury, including the position of the arm, the amount of force applied, and the point of force application [45]. Injury with the arm in extension, abduction, and external rotation favors anterior dislocation, whereas electroshock, seizures, or a fall on the flexed and adducted arm are commonly associated with posterior dislocation [45]. In a posterior traumatic dislocation, the patient may report a direct blow with the arm in forward elevation, adduction, and internal rotation [100]. For recurrent instability, the history defines the initial injury, the position or action that results in instability, how long the shoulder stays out, whether radiographs are available with the shoulder out of joint, and what means have been necessary to reduce the shoulder [45]. The history also solicits evidence of neurologic or rotator cuff problems after previous episodes of shoulder instability [45]. Previous treatment of the recurrent instability, as well as the effectiveness of this treatment, should be documented [45].

Physical Examination

Recognition of a posterior dislocation may be impaired by the lack of a striking deformity and by the fact that the shoulder is held in the traditional sling position of adduction and internal rotation [45]. Asymmetry of the shoulder contours can often best be visualized by viewing the shoulders from above while standing behind the patient [45]. Classic features of a posterior dislocation include limited external rotation of the shoulder, often to less than 0 degrees [45], and limited elevation of the arm, often to less than 90 degrees [45]. Additional classic features include posterior prominence and rounding of the shoulder in comparison to the normal side [45], flattening of the anterior aspect of the shoulder [45], and prominence of the coracoid process on the dislocated side [45].

In posterior dislocation, motion is limited because the head of the humerus is fixed on the posterior glenoid rim by muscle forces, or the head might actually be impaled on the glenoid rim [45]. Clinical examination for posterior shoulder dislocation typically shows an inability to externally rotate the shoulder because of a mechanical block, and limited flexion and abduction [47]. In posterior shoulder dislocation, the dislocated arm is locked in internal rotation because the humeral head is fixed on the posterior glenoid rim [47]. Abduction and forward elevation may be preserved up to 80° or more [47]. With the passage of time, the posterior rim of the glenoid can further impact the fracture of the humeral head and produce a deep hatchet-like defect or a V-shaped compression fracture, which engages the head even more securely [45]. Patients with old, unreduced posterior dislocations of the shoulder can have 30 to 40 degrees of glenohumeral abduction and some humeral rotation as a result of enlargement of the groove [45]. With long-standing disuse of the muscles about the shoulder, atrophy will be present, which accentuates the flattening of the anterior portion of the shoulder, the prominence of the coracoid, and the fullness of the posterior portion of the shoulder [45]. In the interval before the diagnosis of posterior dislocation is made, the injury may be misdiagnosed as a frozen shoulder [45].

An essential part of the physical examination of a dislocated shoulder is assessment of the neurovascular status of the upper extremity and charting of the findings before reduction [45]. Initial examination for shoulder instability should include a complete neurovascular examination to document any neurologic or vascular deficits [103]. Testing of the axillary nerve is performed by assessing light touch over the lateral deltoid and by palpating the deltoid muscle for contraction while having the patient abduct the arm against resistance at the elbow [103]. Documentation of active and passive range of motion of the shoulder for internal and external rotation as well as forward flexion and abduction is important [103]. Marked loss of motion is seen with persistent dislocations and rotator cuff lesions [103]. Rotator cuff testing is an essential part of the shoulder instability examination, particularly in patients over the age of 40 years, as the incidence of rotator cuff lesions increases [103]. The belly press or bear hug test is the most effective test to evaluate the function of the subscapularis in the acutely injured patient [103]. Testing of resisted shoulder abduction in the first 30 degrees of shoulder flexion with the arm internally rotated is effective for evaluating the supraspinatus [103]. Evaluation of the infraspinatus is performed by applying resisted external rotation with the elbow flexed to 90 degrees [103].

The load and shift test is used to evaluate anterior and posterior glenohumeral laxity and is performed while the patient is in a seated or supine position with the humeral head centered in the glenoid fossa and translated [100]. In the load and shift test, Grade 0 means normal translation, Grade 1 is translation to rim and back (less than 1 cm), Grade 2 is translation over the rim followed by spontaneous reduction (1 to 2 cm), and Grade 3 is translation over the rim without spontaneous reduction (greater than 2 cm) [100]. Generalized joint laxity should be assessed using the Beighton score (0–9 point scale) [100]. Bilateral posterior shoulder dislocations with reverse Hill-Sachs lesions are uncommon and prone to misdiagnosis [123].

Diagnostic Challenges and Classification

Patients do not always recognize anterior shoulder instability, and initial physical examination may be limited in the acute setting [31]. The ABC classification distinguishes three groups of posterior shoulder instability based on the nature of pathology (first-time, dynamic, or static) and two different subtypes based on the pathomechanical causes [34]. The B1 subtype is characterized by a pattern in which the instability is caused by pathological activation of the rotator cuff and periscapular muscles [16]. Historically, the absence of structural pathology on diagnostic imaging, coupled with the limited success of conventional treatments, frequently led to the dismissal of dynamic-functional posterior shoulder instability as attention-seeking or psychiatric behavior [16]. This misconception delayed appropriate care and increased the disease burden and social stigmatization for affected patients [16]. Failure of primary shoulder stabilization procedures is often related to uncorrected anatomic pathology [21]. The instability severity index score permits precise identification of patients at risk for failure of primary shoulder stabilization procedures [21].

Investigations

Plain radiography: Standardized plain films are almost always sufficient to garner the information needed for shoulder evaluation [43]. The axillary view taken with the arm in the functional position of elevation is referred to as the "truth view" because it demonstrates glenohumeral relationships in the functional position of elevation [43]. This standardized axillary view enables the detection of posterior subluxation or "functional decentering" that is not evident in images taken with the arm at the side [43]. The axillary view is a necessary view in the evaluation of glenohumeral joint instability and enables determination of the humeral head position in the glenoid fossa [96]. It may detect occult, locked posterior shoulder dislocation in a patient who exhibits a lack of passive external rotation [96]. In a systematic review of posterior shoulder dislocations, 73% of patients had a missed initial diagnosis due to the lack of an axillary view, Y view, or computed tomography imaging [98]. When axillary or Y-view radiographs were made subsequently in patients with missed posterior dislocation diagnoses, the diagnosis was confirmed in 100% of patients [98]. Radiographs can be used for screening patients for significant glenoid bone loss [157]. However, radiographs seem inferior to CT scans for assessing osseous lesions especially at the glenoid rim [68]. The degree of posterior subluxation can be measured by the position of the center of the humeral head in relation to the plane of the scapula, the position of the center of the humeral head in relation to the glenoid face, or the point of contact of the humeral articular surface on the glenoid articular surface [43].

Computed Tomography: CT with three-dimensional reconstructions is the advanced imaging study of choice for determining the extent of glenoid bone loss in the setting of shoulder instability [96]. CT imaging is frequently used to assess for bony lesions in recurrent instability cases [94]. CT scans may offer a few degrees of increased precision in the measurement of glenoid version, but this precision does not necessarily improve the quality of the surgery or the clinical outcome [43]. CT scans have the disadvantage of being taken with the arm in the adducted position [43].

Magnetic Resonance Imaging: MRI is useful to identify osteonecrosis of the humeral head, bone tumours, labral tears, and rotator cuff tears [88]. The accuracy of MRI for identifying labral tears and rotator cuff tears is enhanced by combining the scan with arthrography [88]. T1-weighted MRI can reveal Hill-Sachs lesions and is often used with magnetic resonance arthrograms to provide a more detailed picture of the joint surfaces [94]. T2-weighted MRI provides better visualization of full thickness rotator cuff tears [94]. In patients with suspected posterior glenohumeral instability, imaging of the affected shoulder can show abnormalities of the bone, labrum, and joint capsule [55]. One study investigated and compared morphological factors on magnetic resonance imaging between pain-predominant and apprehension-dominant instability presentations [164]. Regardless of the radiologist interpretation of MRA, patients with symptomatic posterior shoulder instability do benefit from arthroscopic stabilization surgery [26].

Magnetic Resonance Arthrography: MR arthrography is considered the benchmark for evaluation for labral tears [94]. MR arthrography has proven utility by increasing both sensitivity and specificity in detecting injuries to the capsulolabral–ligamentous complex as compared to traditional MRI [92]. In a meta-analysis of the diagnostic test accuracy of MRA compared to MRI for the detection of glenoid labral injuries, MRA sensitivity was 88% and specificity was 93%, compared to MRI sensitivity of 76% and specificity of 87% [92]. MRAs can demonstrate a patulous capsule on the coronal, sagittal, and axial imaging in patients with multidirectional instability [92]. The presence of glenoid dysplasia, increased capsular cross-sectional area, and increased glenoid retroversion have all been found to be associated with increased posterior labral tears and symptomatic instability [92]. Glenoid retroversion was significantly increased in patients with symptomatic posterior labral tears, but there was no significant association between instability and increased humeral head subluxation [92].

Ultrasonography: Ultrasonography is a simple and accurate test for identifying rotator cuff tears and calcific tendinitis [88]. It is a low-cost alternative to MRI and arthrography for evaluating both skeletal and soft-tissue structures of the shoulder [94]. Ultrasonography can provide immediate, real-time visualization of the rotator cuff, biceps tendon, and calcific deposits [94]. However, ultrasonography is highly operator dependent and is not as useful for evaluating labral tears or rotator cuff tears that are very small or larger than 3 cm [94].

Other Considerations: The purpose of imaging of the shoulder is to help establish the diagnosis, determine the severity of the pathoanatomy, assist in surgical planning, and enable the surgeon to illustrate the condition of the shoulder to the patient [43]. Unless a specific research protocol is in place, the temptation to "overimage" should be resisted, obtaining only the scans or reconstructions that are necessary for the care of the patient [43]. Proper radiographic technique is as important as proper surgical technique to achieve the desired outcome [43]. A robust approach to imaging the shoulder needs to recognize that the shoulder is a three-dimensional structure that cannot be represented by a single planar view [90]. Critical relationships, such as the degree of centering of the humeral head, change with the position of the arm [90]. Shoulder pathology may be found in a large number of different bones and soft tissues [90]. Overlying and superimposed structures as well as metallic implants may complicate imaging the structures of interest [90]. Surgeons need to develop a judicious approach that yields the information necessary to treat the patient while avoiding the tendency to "over-image" [90]. A systematic review has identified significant heterogeneity in both the imaging modality and method used to measure glenoid bone loss [165].

Treatment

Non-Operative

Team physicians for National Hockey League players strongly favor nonoperative management during the season for initial posterior instability events of the shoulder [60]. However, there is no evidence regarding the effectiveness of surgical management for post-traumatic chronic shoulder instability [15].

Operative

Indications: Advances in understanding posterior glenohumeral anatomy and biomechanics have guided clinical decision making, including the delineation of surgical indications and contraindications, nonsurgical treatment solutions, and appropriate stabilization and bone augmentation techniques [28]. An isolated reverse Bankart repair with a glenoid defect ≥20% is not sufficient to restore glenohumeral stability [58]. Di Giacomo et al. propose a glenoid defect ≥20% as the cut-off for posterior bone block techniques [58]. The main reported risk factors for failure of isolated soft tissue surgery are female sex, dominant side, concomitant cuff injury, the use of three or fewer anchors in the repair, and a smaller glenoid diameter [58].

Surgical Approach / Technique: Arthroscopic surgical techniques have facilitated successful management of both recurrent posterior subluxations and frank posterior instability [20]. Early and midterm results of arthroscopic stabilization for posterior shoulder instability are promising [6], with good outcomes, high patient satisfaction, and low rates of recurrent instability, revisions, and residual pain [17]. The "pinch-and-tuck" arthroscopic technique is an alternative for capsular plication that effectively and safely addresses capsular laxity in patients with posterior shoulder instability [32]. Single-portal arthroscopic posterior capsulorrhaphy offers an efficient, reproducible procedure to address posterior shoulder instability pathology [19]. The arthroscopic technique for posterior labral repair in the beach-chair position maintains principles of anatomic restoration and reliable fixation while expanding the practical applicability of the beach-chair position [18].

Bone Block Augmentation: Both glenoid osteotomy and bone block procedures can successfully address symptomatic posterior shoulder instability [121]. The arthroscopic posterior bone block procedure with fixation with 2 cortical buttons and a specific glenoid guide offers a safe and reproducible technique for the treatment of posterior shoulder instability [120]. At a minimum of 2 years, successful correction of scapular anatomy can improve static subluxation and restore subjective and objective shoulder stability [5]. There is a moderate rate of recurrence following posterior bone block for posterior shoulder instability [14].

Other Considerations: A glenoid bone defect of 11% increased the risk of failure by 10.4 times, while a 15% defect increased it 24.4 times in patients undergoing arthroscopic capsulolabral repair [58]. Additional long-term randomized trials are needed to better understand the potential advantages and disadvantages of surgical positioning (beach-chair versus lateral decubitus) for posterior shoulder stabilization [1]. The thresholds defined in the 2025 JSES International study can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability, allowing for earlier detection of recurrent posterior instability [3]. Persistence or recurrence of static/dynamic posterior instability after correction of glenoid version alone may be related to incomplete restoration of the intrinsic stability that is conferred by a normal acromial anatomy [13].

Complications

Recurrence and Failure

Recurrence: Arthroscopic stabilization of posterior shoulder instability demonstrates low rates of recurrent instability [17], with early and midterm results considered promising [6]. In contrast, posterior bone block augmentation for recurrent posterior shoulder instability is associated with high rates of clinical failure [2]. A cohort of traumatic posterior glenohumeral dislocations observed a high failure rate, with 19 out of 33 shoulders (58%) experiencing structural failure such as recurrent dislocation or revision surgery [173]. The high rate of persistent instability following glenoid osteotomy for posterior shoulder instability should be considered when making treatment decisions [182]. Surgical stabilization is generally not recommended for dynamic-functional posterior instability, as it is associated with poor outcomes [16].

Bony and Hardware Complications

Bone Loss and Defects: Posterior glenohumeral instability events were associated with glenoid bone loss of 5% [108]. Loss of stability from a humeral head defect is significantly magnified at functional arm positions of increased abduction and external rotation rather than a resting arm position [24]. Recurrence of instability was significantly more frequent when bone union failed after arthroscopic bony Bankart repair for traumatic anterior shoulder instability with a glenoid defect [180].

Hardware and Graft Issues: Graft non-union with bent or broken screws is a potential complication of glenoid bone augmentation [151]. Osteolysis or reabsorption of the proximal part of the grafts with prominent hardware is a potential complication of glenoid bone augmentation [151]. Long-term degenerative changes and osteoarthritis are potential complications of glenoid bone augmentation [151]. There was a lower rate of hardware complications in second-generation arthroscopic anatomic glenoid reconstruction using customized distal tibial allografts, with no patients requiring revision surgery for hardware removal [181].

Neurological and Soft Tissue Complications

Nerve Injury: The musculocutaneous, axillary, and suprascapular nerves are surrounding structures at risk during glenoid bone augmentation [151]. Nerve injuries occur in 94% of patients with scapulothoracic dissociation, and brachial plexus paralysis is usually complete [149]. Partial damage is more frequently observed in retro- and infraclavicular injuries, and spontaneous recovery occurs in some cases but is never complete [149]. Nerve reconstruction by neurotization and/or nerve graft is preferably performed within a period of 2 to 6 months of the accident [149].

Soft Tissue and Range of Motion: Decreased range of motion is a potential complication of glenoid bone augmentation [151]. Coracoid transfers for shoulder instability are associated with a broad range and significant incidence of complications [10].

Diagnostic and Management Challenges

Clinical Presentation: Patients with classic posterior instability have no identifiable mechanism of injury and their primary symptom is pain [49].

Evidence Heterogeneity: Because of significant heterogeneity in the clinical outcomes reported to date, further research will be necessary to define the clinical outcomes in revision posterior stabilization [29].

Recovery

Light activity (weeks): The evidence provided does not specify a typical week range for the resumption of desk work, driving, or light activities of daily living following arthroscopic posterior shoulder stabilization.

Full activity (months): Return to sport after arthroscopic posterior shoulder stabilization occurs at a high rate, ranging from 4.3 to 8.6 months after surgery [25]. Athletes who underwent surgical treatment for posterior shoulder instability demonstrated high rates of return to sport and relatively high rates of return to preinjury level of sport [66]. Arthroscopic posterior Bankart repair for traumatic posterior shoulder instability in collision sports athletes resulted in a high return-to-play rate [158].

Complete recovery / outcome plateau (months): The provided evidence does not define a specific month range for when pain, strength, and final functional outcomes stabilize.

Rehabilitation protocol: The recommended initial treatment for microtraumatic posterior shoulder instability is rehabilitation [33]. Participants with microtraumatic posterior shoulder instability who completed a 24-week posterior instability rehabilitation program showed significant improvements in patient-reported outcome measures at 12 weeks [33]. Scapular dyskinesis and SICK syndrome secondary to chronic type III acromioclavicular dislocation can be treated with a rehabilitation protocol resulting in positive improvements of shoulder function within 6 weeks [134]. Patients with scapular dyskinesis and SICK syndrome who do not respond to a rehabilitation programme will not improve with extended rehabilitation time [134]. Postoperative scapular dyskinesis following a Latarjet procedure resolved in four out of five patients with 6 months of a specific rehabilitation protocol [136].

Functional milestones: Defined thresholds for clinical significance can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability [3]. These thresholds allow for earlier detection of recurrent posterior instability [3].

Other Considerations: No additional recovery-relevant content is present in the evidence base beyond the protocols and milestones described above.

Key Evidence

• [L4] Additional long-term randomized trials comparing these positions are needed to better understand the potential advantages and disadvantages of surgical positioning for posterior shoulder stabilization. [1] (10.1177/2325967118822452)
• [L1] Posterior bone block augmentation for recurrent posterior shoulder instability does not reliably yield substantial improvements in patient-reported outcomes, and complications are frequently observed. [2] (10.1016/j.arthro.2021.07.018)
• [L4] The thresholds defined in this study can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability, allowing for earlier detection of recurrent posterior instability. [3] (10.1016/j.jseint.2025.08.006)
• [L5] Soft-tissue stabilization alone may not be sufficient in patients who present with substantial bone loss to the posterior glenoid and/or the anterior humeral head. [4] (10.2106/jbjs.rvw.23.00243)
• [L4] At a minimum of 2 years successful correction of scapular anatomy can improve static subluxation and restore subjective and objective shoulder stability. [5] (10.1016/j.jseint.2025.06.018)
• [L1] The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising. [6] (10.1016/j.arthro.2014.11.009)
• [L5] Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays. [8] (10.5435/00124635-200608000-00004)
• [L4] Arthroscopic management of posterior-inferior shoulder instability has a successful track record and minimal complication profile. [9] (10.1016/j.arthro.2018.06.057)
• [L1] Coracoid transfers for shoulder instability can improve shoulder stability with acceptable recurrence rates but are challenging procedures associated with a broad range and significant incidence of complications. [10] (10.1016/j.jse.2012.02.008)
• [L4] The iliac posterior shoulder bone-block is effective in managing instances of involuntary posterior shoulder instability, showing satisfactory results in terms of non-recurrence, pain relief, and function recovery. [12] (10.1016/j.otsr.2008.09.008)
• [L5] Persistence or recurrence of static/dynamic posterior instability after correction of glenoid version alone may be related to incomplete restoration of the intrinsic stability that is conferred by a normal acromial anatomy. [13] (10.1186/s40634-023-00623-x)
• [L4] There is a moderate rate of recurrence following posterior bone block for posterior shoulder instability. [14] (10.1016/j.jse.2021.06.013)
• [L1] There was no evidence regarding the effectiveness of surgical management for post-traumatic chronic shoulder instability. [15] (10.1136/bjsports-2017-098539)
• [L5] [16] (10.1016/j.xrrt.2026.100861)
• [L4] Arthroscopic stabilization of posterior shoulder instability resulted in good outcomes with high patient satisfaction and low rates of recurrent instability, revisions, and residual pain. [17] (10.1016/j.jse.2024.04.006)
• [L5] This technique maintains the principles of anatomic restoration and reliable fixation while expanding the practical applicability of the beach-chair position for posterior shoulder instability. [18] (10.1002/atn2.70225)
• [L5] All in all, this technique offers an efficient, reproducible procedure to address posterior shoulder instability pathology. [19] (10.1016/j.eats.2022.05.004)
• [L5] The article outlines the evolution of diagnostic acumen and treatment algorithms for posterior shoulder instability, emphasizing that arthroscopic surgical techniques have facilitated successful management of both recurrent posterior subluxations and frank posterior instability. [20] (10.1016/j.csm.2008.06.001)
• [L5] Failure of primary shoulder stabilization procedures is often related to uncorrected anatomic pathology, and the instability severity index score permits precise identification of patients at risk. [21] (10.1016/j.arthro.2010.11.057)
• [L4] Overall, male patients were significantly more likely to have anterior shoulder instability, while female patients were significantly more likely to have posterior shoulder instability. [22] (10.1177/23259671211006437)
• [L3] Coracoid morphology differs significantly in patients undergoing posterior shoulder stabilization when compared to patients undergoing surgery for anterior instability or a comparison cohort. [23] (10.1177/03635465261421534)
• [L5] Loss of stability from a humeral head defect is significantly magnified at functional arm positions of increased abduction and external rotation rather than a resting arm position. [24] (10.1016/j.arthro.2015.04.013)
• [L4] There is a high rate of return to sport after arthroscopic posterior shoulder stabilization, ranging from 4.3 to 8.6 months after surgery. [25] (10.1016/j.asmr.2020.08.007)
• [L3] Regardless of the radiologist interpretation of MRA, patients with symptomatic posterior shoulder instability do benefit from arthroscopic stabilization surgery. [26] (10.1016/j.xrrt.2026.100675)
• [L5] Advances in understanding posterior glenohumeral anatomy and biomechanics have improved comprehension of this challenging disorder and helped guide clinical decision making, including delineation of surgical indications and contraindications, nonsurgical treatment solutions, and appropriate stabilization and bone augmentation techniques. [28] (10.5435/jaaos-d-15-00631)
• [L4] Because of significant heterogeneity in the clinical outcomes reported to date further research will be necessary to define the clinical outcomes in revision posterior stabilization. [29] (10.1016/j.jse.2012.11.019)
• [L3] Patients do not always recognize anterior shoulder instability, and initial physical examination may be limited in the acute setting. [31] (10.1177/23259671251414851)
• [L5] The article presents an alternative technique for capsular plication that effectively and safely addresses capsular laxity in patients with posterior shoulder instability. [32] (10.1016/j.eats.2025.103794)
• [L4] [33] (10.1016/j.jseint.2024.09.016)
• [L5] [34] (10.1530/eor-24-0025)
• [L4] [47] (10.1016/j.arthro.2011.06.015)
• [L4] [48] (10.2106/00004623-195638050-00001)
• [L2] Patients with anterior instability present primarily with an identifiable mechanism of injury and complaints of instability, whereas most patients with classic posterior instability have no identifiable mechanism of injury and their primary symptom is pain. [49] (10.1177/0363546518819199)
• [L5] In patients with suspected posterior glenohumeral instability, imaging of the affected shoulder can show abnormalities of the bone, labrum, and joint capsule. [55] (10.2214/ajr.07.3849)
• [L5] [58] (10.1530/eor-22-0009)
• [L4] NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder. [60] (10.1177/23259671261440208)
• [L4] This review provides an up-to-date insight into the aetiology of posterior shoulder dislocations, showing that seizures were most commonly implicated. [61] (10.1302/0301-620x.101b1.bjj-2018-0984.r1)
• [L4] The systematic review demonstrated high rates of return to sport and relatively high rates of return to preinjury level of sport among all athletes who underwent surgical treatment for posterior shoulder instability. [66] (10.1016/j.jseint.2020.08.002)
• [L3] Radiographs seem inferior to CT scans for assessing osseous lesions especially at the glenoid rim. [68] (10.1016/j.jse.2013.04.020)
• [L3] Posterior glenohumeral instability events were associated with glenoid bone loss of 5%. [108] (10.1177/03635465221115828)
• [L4] The arthroscopic posterior bone block procedure with fixation with 2 cortical buttons and a specific glenoid guide offers a safe and reproducible technique for the treatment of posterior shoulder instability. [120] (10.1016/j.eats.2023.05.023)
• [L1] Both glenoid osteotomy and bone block procedures can successfully address symptomatic posterior shoulder instability. [121] (10.1016/j.xrrt.2025.03.004)
• [L4] Bilateral posterior shoulder dislocations with reverse Hill-Sachs lesions are uncommon and prone to misdiagnosis; early recognition and tailored treatment strategies are essential for satisfactory functional outcomes. [123] (10.1186/s12891-026-09537-y)
• [L4] Scapular dyskinesis and SICK syndrome secondary to chronic type III AC dislocation can be treated with the proposed rehabilitation protocol resulting in positive improvements of the shoulder function within 6 weeks; however, patients that do not respond to the rehabilitation programme will not improve with extended rehabilitation time. [134] (10.1007/s00167-014-2844-5)
• [L3] Four/5 resolved with 6 months of specific rehabilitation protocol. [136] (10.1016/j.jseint.2025.101510)
• [L4] [149] (10.1054/jhsb.2000.0393)
• [L5] [151] (10.1136/jisakos-2019-000413)
• [L4] Radiography can be used for screening patients for significant glenoid bone loss. [157] (10.1186/s12891-015-0607-1)
• [L4] Arthroscopic posterior Bankart repair for traumatic posterior shoulder instability in collision sports athletes resulted in a low recurrence rate, high return-to-play rate, and clinically meaningful improvement. [158] (10.1016/j.asmr.2025.101264)
• [L4] The study investigated and compared morphological factors on magnetic resonance imaging between pain-predominant (UPS) and apprehension-dominant (ASI) instability presentations. [164] (10.1016/j.xrrt.2026.100810)
• [L1] This systematic review has identified significant heterogeneity in both the imaging modality and method used to measure glenoid bone loss. [165] (10.1302/0301-620x.104b1.bjj-2021-0751.r1)
• [L4] The study found a high failure rate in both cohorts, with 19 out of 33 shoulders (58%) experiencing structural failure such as recurrent dislocation or revision surgery. [173] (10.1016/j.jseint.2026.101773)
• [L3] Recurrence of instability was significantly more frequent when bone union failed. [180] (10.1177/0363546515571555)
• [L3] There was a lower rate of hardware complications in the G2 group, with no patients requiring revision surgery for hardware removal. [181] (10.1016/j.jisako.2025.100773)
• [L4] However, the high rate of persistent instability should be considered when making treatment decisions. [182] (10.1177/17585732211056053)

See Also

• Shoulder Instability
• Os Acromiale
• Rotator Cuff
• Fractures
• Frozen Shoulder
• Calcific Tendinitis
• Latarjet Procedure

References

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