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Posterior shoulder stabilisation

98 citationsUpdated Oct 2026

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

Overview

Arthroscopic stabilization for posterior shoulder instability demonstrates promising early and midterm results, characterized by high patient satisfaction and low rates of recurrent instability, revisions, and residual pain [4, 17]. This arthroscopic approach maintains a successful track record with a minimal complication profile [7]. Patients with symptomatic posterior shoulder instability benefit from this surgical intervention regardless of the radiologist’s interpretation of the magnetic resonance arthrogram [41]. Following surgery, there is a high rate of return to sport, typically occurring between 4.3 and 8.6 months post-operatively [24]. Recent 2025 thresholds provide a guideline for interpreting patient outcomes, facilitating earlier detection of recurrent posterior instability [2].

Surgical success depends on addressing underlying anatomic pathology, as failure of primary stabilization is often related to uncorrected structural deficits [28]. The instability severity index score permits precise identification of patients at risk for such failure [28]. In patients presenting with substantial bone loss to the posterior glenoid and/or the anterior humeral head, soft-tissue stabilization alone may not be sufficient [11]. While posterior bone block augmentation does not reliably yield substantial improvements in patient-reported outcomes and is frequently associated with complications [9], the iliac posterior shoulder bone-block remains effective for involuntary posterior instability, showing satisfactory results in non-recurrence, pain relief, and function recovery [12]. Additionally, successful correction of scapular anatomy at a minimum of 2 years can improve static subluxation and restore subjective and objective shoulder stability [3].

The clinical evaluation must consider the entity of posterior-lateral shoulder capsule disruption in patients exhibiting posterior shoulder pain or instability after a traumatic event [8]. Coracoid morphology differs significantly in patients undergoing posterior stabilization compared to those undergoing anterior instability surgery or a comparison cohort [22]. Persistence or recurrence of static and dynamic posterior instability after correction of glenoid version alone may be related to incomplete restoration of intrinsic stability conferred by normal acromial anatomy [13]. Arthroscopic techniques, including the "pinch-and-tuck" capsular plication [34], single-portal posterior capsulorrhaphy [19], and posterior labral repair in the beach-chair position [18], effectively address capsular laxity and pathology while maintaining principles of anatomic restoration and reliable fixation. Further long-term randomized trials are needed to better understand the potential advantages and disadvantages of surgical positioning, specifically comparing beach-chair and lateral decubitus positions [1].

Anatomy & Pathophysiology

Bony Anatomy

The glenoid is a convex structure of shallow depth shaped like an inverted pear [72]. The glenoid cavity is a shallow socket, approximately one third the size of the humeral head [73]. The subchondral bone of the glenoid is relatively flat, with articular concavity augmented by cartilage and a circumferential labrum [75]. The glenoid averages 5° of retroversion in relation to the axis of the scapular body [75]. The glenoid articular surface radius of curvature is 2 to 3 mm larger than that of the humeral head [84]. The glenoid is encircled by the labrum, which increases the depth of the socket by 50% around the humeral head [85]. The glenoid articular surface and labrum combine to create a socket approximately 9 mm deep in the superoinferior direction and 5 mm deep in the anteroposterior direction [85].

The humeral head is spherical with a diameter of 37 to 57 mm [72]. The humeral head averages 19° of retroversion and 41° of inclination (neck-shaft angle) [75]. The average neck-shaft angle of the humerus is 45 degrees (±5 degrees) [84]. The humeral head is retroverted 30 degrees relative to the transepicondylar axis of the humerus [86]. The distance from the lateral base of the coracoid process to the lateral margin of the greater tuberosity is called the lateral humeral offset [84].

The scapula is attached to the axial skeleton by the acromioclavicular and sternoclavicular joints [74]. The scapula is separated from the chest wall by thin gliding fibro-fatty tissue, allowing smooth excursion over the chest wall [74]. The scapula is anteverted on the chest wall approximately 30 degrees relative to the body [86]. The glenoid is connected with the flat body of the scapula by the scapular neck [74]. Two bony pillars, the lateral pillar and the spinal pillar, transmit compressive forces from the glenoid fossa and form the basic load-bearing structure of the scapular body [74]. The weakest bone in the scapula is located primarily in the central part of the biomechanical body, specifically in the infraspinous fossa [74]. The weakest area of the circumference of the biomechanical body of the scapula is the spinomedial angle, where the scapular spine connects to the medial border [74].

The hook-shaped coracoid process curves forwards from the superior surface of the scapular neck [74]. The scapular spine ends in a flattened bony process, the acromion, which curves forwards [74]. The acromion has three ossification centers: the metacromion (base), the mesoacromion (middle), and the preacromion (tip) [75]. The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch, a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [72]. The acromion acts as a mechanical buttress to posterior humeral head displacement [123].

The proximal humerus has three centers of ossification: the humeral head, greater tuberosity, and lesser tuberosity [75]. The primary blood supply to the humeral head is provided by the anterolateral ascending branch of the anterior humeral circumflex artery, which enters the head as the arcuate artery [75]. The posterior humeral circumflex artery provides 64% of the humeral head blood supply [79].

Soft Tissue Anatomy

The rotator cuff consists of the subscapularis, supraspinatus, infraspinatus, and teres minor muscles [73]. The subscapularis inserts on the lesser tuberosity and causes medial displacement of the humerus [72]. The supraspinatus and infraspinatus insert on the greater tuberosity and cause superior and posterior displacement of the humerus [72]. The pectoralis major inserts on the humeral shaft and displaces it medially [72]. The pectoralis major stabilizes the glenohumeral joint by resisting superior migration of the humeral head [26]. The pectoralis major enhances scapulothoracic stabilization of the latissimus dorsi and deltoid muscles [26].

The rotator interval is defined medially by the base of the coracoid, superiorly by the supraspinatus tendon, and inferiorly by the subscapularis tendon [75]. The rotator interval contains the coracohumeral ligament, the superior glenohumeral ligament, and the intra-articular portion of the long head of the biceps tendon [75]. The coracohumeral ligament restricts external rotation in adduction and is a static restraint to inferior and posterior translation in adduction and external rotation [75]. The superior glenohumeral ligament is a primary static restraint against anterior translation with the arm at the side [75]. The middle glenohumeral ligament is a primary static restraint against anterior translation with the arm in external rotation and 45° of abduction [75]. The posterior band of the inferior glenohumeral ligament is a primary static restraint against posterior-inferior translation in internal rotation and adduction [75].

The posterior capsule is thin compared to the anterior capsule [105]. The posterior capsule and the buttress provided by the posterior glenoid labrum are the primary static stabilizers to unidirectional posterior translation [105]. The posterior band of the inferior glenohumeral ligament is thinner than the anterior band [136]. The subscapular bursa lies between the subscapularis tendon and the neck of the scapula and communicates with the joint cavity between the superior and middle glenohumeral ligaments [76].

The serratus anterior muscle plays a key role in scapulothoracic rhythm [105]. The trapezius consists of upper, middle, and lower portions that elevate, rotate, and retract the scapula [70]. The trapezius is innervated by the spinal accessory nerve (11th cranial nerve) [70]. The long head of the biceps has a pertinent biomechanical role in glenohumeral stability regardless of the condition of the superior labrum [124].

Vascular & Neural Anatomy

The axillary nerve is a terminal branch of the posterior cord of the brachial plexus that passes beneath the conjoined tendon anterior to the subscapularis [78]. The axillary nerve enters the quadrilateral space posteriorly and splits into anterior and posterior branches [78]. The anterior and middle deltoid muscle receives sole innervation from the anterior branch of the axillary nerve [78]. The posterior deltoid muscle innervation varies, with supply from both branches in 89.1% of cases [78].

The superior transverse scapular ligament arises from the medial base of the coracoid overlying the suprascapular notch [75]. The suprascapular artery runs superior to the superior transverse scapular ligament, and the nerve runs deep to it [75]. Entrapment of the suprascapular nerve at the superior transverse scapular ligament causes denervation of both the supraspinatus and the infraspinatus [75]. The spinoglenoid ligament overlies the suprascapular nerve at the spinoglenoid notch [75]. Entrapment, traction, or compression at the spinoglenoid notch causes denervation of the infraspinatus [75].

Pathophysiology & Biomechanics

The glenohumeral joint relies upon a concavity-compression mechanism to remain concentrically reduced [33]. Glenoid retroversion, glenoid dysplasia, posterior glenoid bone defects, and dynamic glenoid malpositioning can contribute to posterior instability [33]. Posterior translation is highly sensitive to small degrees of posterior glenoid defects or retroversion [33]. The glenoid dynamically changes position with scapular movement [33]. Recurrence of instability after surgery is reliably related to a failure to address one of the glenohumeral stabilizers or the development of a new lesion in these structures [33]. The most relevant lesions for posterior instability include deficiency or malpositioning of the glenoid fossa, tearing or attenuation of the posterior labrum, and laxity within the anterior or posterior capsuloligamentous structures [33].

The most consistent finding in patients with recurrent posterior subluxation is a patulous posterior capsule [105]. The posterior capsule either stretches over time or tears as a result of single event trauma and heals in an elongated position, thereby increasing capsular volume [105]. Posterior labral tears in recurrent posterior subluxation are generally degenerative tears rather than capsular and labrum avulsions [105]. Dysfunction of scapulothoracic rhythm may compromise the stability of the glenohumeral joint [105]. Paralysis of the serratus anterior results in scapular winging and loss of power in elevation that potentially may influence glenohumeral stability [105].

Glenoid as well as acromial malalignment alone is associated with pathological posterior translation of the humeral head upon simulated active elevation [114]. Glenohumeral contact patterns highly depend on the amount of glenoid retroversion and posterior labral and/or bony glenoid integrity [120]. Current glenoid bone loss measurements are unable to provide an adequate estimation of the actual biomechanical effect of glenoid defects because the relation between defect size and biomechanical effect is nonlinear [110]. Patients with shoulder instability have constitutional biomechanically relevant glenoid concavity shape differences [110]. The presence of a large glenoid defect was associated with a 65% to 80% reduction in joint stability parameters [126]. Posterior and posterior superior labral injuries produce alterations in glenohumeral kinematics with implications for joint instability, increased joint loading, and potential joint damage [122].

Microtraumatic posterior shoulder instability is characterized by symptomatic posterior translation of the glenohumeral joint [35]. A common etiology of microtraumatic posterior shoulder instability is a gradual overload of glenohumeral joint structures [35]. The mechanism of injury for microtraumatic posterior shoulder instability involves repetitive loading of the shoulder in a combination of flexion, adduction, and internal rotation [147]. Repetitive forces acting on the posterior glenohumeral joint capsulolabral complex and rotator cuff can result in posterior capsulolabral lesions, deformation, and articular surface rotator cuff tears [147].

Static posterior subluxation is a fixed posterior position of the humeral head on the glenoid fossa on CT or MRI scans with the arm in neutral rotation [99]. Static posterior subluxation is most frequently but not always associated with congenital dysplasia of the glenoid or with degenerative glenohumeral joint disease [99]. Static posterior subluxation may be present without any rotator cuff deficiencies [99]. Most authors have found static posterior subluxations to be irreversible [99]. Patients with constitutional static posterior shoulder instability (Type C1) differ from healthy controls regarding osseous scapular and humeral morphology, scapulothoracic orientation, and shoulder girdle muscle distribution [134].

The ABC classification distinguishes three groups of posterior shoulder instability based on the nature of pathology: first-time (Type A), dynamic (Type B), and static (Type C) [26]. Type B dynamic instability is further divided into functional (B1) and structural (B2) subtypes [26]. Type B1 functional instability is characterized by pathological activation of the rotator cuff and periscapular muscles [26]. Historically, the absence of structural pathology on diagnostic imaging for dynamic-functional instability led to its dismissal as attention-seeking or psychiatric behavior [26]. Surgical stabilization is generally not recommended for dynamic-functional instability, as it is associated with poor outcomes [26]. The current gold standard for dynamic-functional instability focuses on normalizing pathological muscle activation patterns [26]. This patient-specific procedure addresses the underlying morphologic abnormality while preserving native glenoid anatomy [61]. Advances in understanding posterior glenohumeral anatomy and biomechanics have improved comprehension of this challenging disorder and helped guide clinical decision making [30].

General Shoulder Biomechanics

The shoulder is composed of four articulations: the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic joints [85]. Normal function of the shoulder is a balance between mobility and stability [85]. The bony anatomy contributes little to stability and has been compared with a golf ball on a tee [85]. The ligamentous constraints are the primary stabilizers at extremes of motion [85]. The superior glenohumeral ligament is the primary restraint to inferior humeral subluxation in 0 degrees of abduction [85]. Tightening of the rotator interval decreases posterior and inferior translation [85]. The middle glenohumeral ligament limits external rotation when the arm is in the lower and middle ranges of abduction but has little effect when the arm is in 90 degrees of abduction [85].

The inferior glenohumeral ligament is composed of an anterior band, a posterior band, and a thinner intervening axillary pouch, creating a hammock-type sling [85]. With internal rotation, the posterior band of the inferior glenohumeral ligament tightens and the anterior band fans out [85]. The anteroinferior glenohumeral ligament complex is the main stabilizer to anterior and posterior stresses when the shoulder is abducted 45 degrees or more [85]. Extrinsic muscles dynamically position the scapula to place the glenoid opposite the humeral head as the shoulder moves [85]. Rotator cuff activity and biceps activity stiffen the capsule and decrease glenohumeral translation [85]. The most important force couple for stability involves the subscapularis and posterior rotator cuff [85]. The teres minor has a heightened contribution to rotator cuff function, particularly when other cuff tendons fail [85].

The tendons of the infraspinatus and supraspinatus muscles join approximately 15 mm proximal to their insertion and cannot be readily separated by blunt dissection [85]. The infraspinatus and teres minor fuse near their musculotendinous junctions [85]. The supraspinatus and subscapularis tendons join as a sheath that surrounds the biceps tendon at the entrance of the bicipital groove [85]. The coracohumeral ligament is a thick band of fibrous tissue extending from the coracoid process along the surface of the capsule to the tuberosities between the supraspinatus and subscapularis tendons [85].

The posterior SC joint capsule and ligaments are the primary stabilizers to anterior and posterior translation of the medial clavicle [75]. The superior and posterior AC ligaments are the primary stabilizers to anterior and posterior (horizontal) translation of the clavicle [75]. The coracoclavicular ligaments are the primary stabilizers to superior (vertical) translation of the distal clavicle [75]. The SSSC provides a stable connection between the scapula and the axial skeleton [75]. The SSSC is composed of the glenoid, the coracoid process, the coracoclavicular ligaments, the distal clavicle, the AC joint, and the acromion [75]. The superior strut of the SSSC comprises the middle clavicle [75]. The inferior strut of the SSSC comprises the lateral scapular border/spine of the scapula [75]. The SC joint is the only true diarthrodial articulation between the upper appendicular and axial skeletons [75]. The AC joint is a small diarthrodial joint with an interposed fibrocartilaginous disk [75].

The subscapularis originates from the anterior scapula and inserts anteriorly onto the lesser tuberosity [79]. The greater tuberosity provides attachment superiorly and posteriorly for the supraspinatus, infraspinatus, and teres minor [79]. The deltoid forward flexes and abducts the shoulder and courses from the clavicle and acromion superiorly into a common tendinous insertion onto the lateral upper third of the humeral shaft [79]. The pectoralis major powers adduction and internal rotation due to its tendinous insertion anteriorly onto the lateral wall of the bicipital groove [79]. The pectoralis major forms the roof of the distal continuation of the bicipital tunnel [79].

Classification

ABC Classification: This system distinguishes three groups of posterior shoulder instability (PSI) based on the nature of pathology: first-time (Type A), dynamic (Type B), and static (Type C) [37]. Type B is further divided into functional (B1) and structural (B2) dynamic instability [26]. The B1 subtype is characterized by instability caused by pathological activation of the rotator cuff and periscapular muscles [26]. 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 [26]. Surgical stabilization is generally not recommended for dynamic-functional instability due to associated poor outcomes [26].

Malgaigne Classification: Created in 1885, this classification is based on the position the humeral head rests in posterior dislocation, distinguishing between subacromial and subspinous types [49]. A third type of posterior dislocation, the subglenoid position, was described in addition to Malgaigne's subacromial and subspinous types [49].

Hawkins Classification: This system considers the time between onset of the lesion and treatment but excludes cases with proximal humerus fractures [49].

Neer Classification: Unlike the Hawkins system, Neer's classification includes fractures of the proximal humerus [49].

Randelli Classification: This classification is applicable only to chronic cases of posterior dislocation [49].

Walch Classification: Walch classified glenoid morphology into subtypes based on specific deformities. Type B1 glenoids are characterized by posterior humeral head subluxation with glenoid retroversion [140]. Type B2 glenoids exhibit a biconcave deformity [140]. Type B3 glenoids are monoconcave and posteriorly worn, with at least 15 degrees of retroversion or at least 70% posterior humeral head subluxation, or both [140]. Type C glenoids have a premorbid retroversion of 25 degrees [140]. Type D glenoids have anteversion or humeral head subluxation of less than 40% [140]. Tightening of the anterior capsule can result in posterior displacement of the head, resulting in severe B2 and B3 deformities [140].

Samilson and Prieto Classification: This radiographic system stages postdislocation glenohumeral arthropathy, which was later expanded by Buscayret et al. by differentiating stage 3 into two stages [140]. Radiographs of post-dislocation arthropathy typically demonstrate joint space narrowing, osteophyte and cyst formation, subchondral sclerosis, and posterior glenoid wear [140]. The presence of radiographic changes does not necessarily correlate with symptoms or subjective assessment of function [140]. CT may be more effective at detecting arthritic changes after dislocation than radiographs [140].

Ideberg Classification: This system provides a detailed framework for intra-articular glenoid fractures. Type I fractures involve the glenoid rim and are frequently associated with glenohumeral dislocation [65]. Goss subclassified Ideberg Type I fractures into Type Ia (anterior glenoid rim fracture) and Type Ib (posterior rim fracture) [65]. Goss also added Type VI to the glenoid fracture classification, representing a highly comminuted glenoid fossa fracture [65].

Other Considerations: Dislocations occurred anteriorly in 98% of patients and posteriorly in 2% in a 1956 study [48]. Dislocations are grouped as atraumatic and traumatic, with atraumatic dislocations accounting for 4.4% of cases [48]. 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 frequently have hyperflexible joints and relatively poor supporting muscles of the shoulder joint [48]. Traumatic dislocations are characterized by more common humeral head defects and usually normal supporting muscles of the shoulder [48]. The incidence of recurrence for traumatic dislocations is 57%, compared to 86% for atraumatic dislocations [48]. Coracoid morphology differs significantly in patients undergoing posterior shoulder stabilization compared to patients undergoing surgery for anterior instability or a comparison cohort [22].

Clinical Presentation

History and Mechanism

Patients with classic posterior shoulder instability often present without an identifiable mechanism of injury, with pain as the primary symptom [50]. Posterior dislocation is commonly associated with electroshock, seizures, or a fall on the flexed and adducted arm [46]. In traumatic posterior dislocation, patients may report a direct blow with the arm in forward elevation, adduction, and internal rotation [104]. Recurrent posterior shoulder instability is an uncommon condition that is often unrecognized, leading to incorrect diagnoses and delays [6]. The history should define the mechanism of injury, including the position of the arm, the amount of force applied, and the point of force application [46]. For recurrent instability, the history should define the initial injury, the position or action that results in instability, how long the shoulder stays out, and what means were necessary to reduce the shoulder [46]. The history should solicit evidence of neurologic or rotator cuff problems after previous episodes of shoulder instability [46]. Patients with posterior shoulder instability may exhibit posterior shoulder pain or instability after a traumatic event [8]. Microtraumatic posterior shoulder instability is characterized by symptomatic posterior translation of the glenohumeral joint, often due to gradual overload of glenohumeral joint structures [35]. Female patients are significantly more likely to have posterior shoulder instability compared to male patients [21].

Physical Examination Findings

Recognition of a posterior dislocation may be impaired by the lack of striking deformity and the shoulder being held in the traditional sling position of adduction and internal rotation [46]. Classic features of a posterior dislocation include limited external rotation of the shoulder, often to less than 0 degrees [46]. Classic features of a posterior dislocation include limited elevation of the arm, often to less than 90 degrees [46]. Classic features of a posterior dislocation include posterior prominence and rounding of the shoulder in comparison to the normal side [46]. Classic features of a posterior dislocation include flattening of the anterior aspect of the shoulder [46]. Classic features of a posterior dislocation include prominence of the coracoid process on the dislocated side [46]. Asymmetry of shoulder contours can often best be visualized by viewing the shoulders from above while standing behind the patient [46]. Motion is limited in posterior dislocation because the head of the humerus is fixed on the posterior glenoid rim by muscle forces or is impaled on the glenoid rim [46]. Patients with old, unreduced posterior dislocations can have 30 to 40 degrees of glenohumeral abduction and some humeral rotation as a result of enlargement of the groove [46]. Long-standing disuse of muscles about the shoulder leads to atrophy, which accentuates the flattening of the anterior portion of the shoulder, prominence of the coracoid, and fullness of the posterior portion [46].

Clinical examination for posterior shoulder dislocation typically shows an inability to externally rotate the shoulder due to a mechanical block [47]. Clinical examination for posterior shoulder dislocation typically shows limited flexion and abduction [47]. 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 degrees or more in posterior shoulder dislocation [47]. Posterior instability is assessed in the supine position with posterior displacement of the glenohumeral joint as the shoulder is internally rotated [51]. The apprehension and relocation tests may be used to augment findings of the physical exam but should not be relied upon exclusively because they are nonspecific [51]. It is not uncommon to see patients with presumed traumatic anterior shoulder instability who in fact have posterior instability, emphasizing the importance of the physical examination [51]. The opposite shoulder is assessed to ascertain the degree of physiologic ligamentous laxity normally present for the individual [51]. Generalized ligamentous laxity may be evaluated by examining for elbow hyperextension and hyperextension of the metacarpophalangeal joint of the thumb [51].

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 [104]. Grade 0 on the load and shift test indicates normal translation [104]. Grade 1 on the load and shift test indicates translation to the rim and back, less than 1 cm [104]. Grade 2 on the load and shift test indicates translation over the rim followed by spontaneous reduction, 1 to 2 cm [104]. Grade 3 on the load and shift test indicates translation over the rim without spontaneous reduction, greater than 2 cm [104]. Generalized joint laxity should be assessed using the Beighton score, a 0–9 point scale [104]. A complete neurovascular examination is required to document any neurologic or vascular deficits in patients with a history of shoulder subluxations or dislocation events [107]. 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 [107]. 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 [107]. Marked loss of motion is seen with persistent dislocations and rotator cuff lesions [107]. Rotator cuff testing is an essential part of the shoulder instability examination, particularly in patients over the age of 40 years [107]. The belly press or bear hug test is the most effective test to evaluate the function of the subscapularis in the acutely injured patient [107]. Testing of resisted shoulder abduction in the first 30 degrees of shoulder flexion with the arm internally rotated is effective for evaluating the supraspinatus [107]. Evaluation of the infraspinatus is performed by applying resisted external rotation with the elbow flexed to 90 degrees [107]. Patients with shoulder instability may experience symptoms of pain coupled with restricted shoulder motion [107].

Diagnostic Challenges and Misdiagnosis

Posterior dislocation may be misdiagnosed as a frozen shoulder, for which vigorous therapy may be mistakenly instituted in an attempt to restore range of motion [46]. In the interval before the diagnosis of posterior dislocation is made, the injury may be misdiagnosed as a frozen shoulder [46]. Bilateral posterior shoulder dislocations with reverse Hill-Sachs lesions are uncommon and prone to misdiagnosis [133]. Patients do not always recognize anterior shoulder instability, and initial physical examination may be limited in the acute setting [32]. 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 instability as attention-seeking or psychiatric behavior [26]. This misconception delayed appropriate care and increased the disease burden and social stigmatization for affected patients [26]. The severe subjective suffering and functional limitations experienced by patients with dynamic-functional posterior instability have challenged the historical dismissal of this condition [26].

Imaging and Assessment

In patients with suspected posterior glenohumeral instability, imaging of the affected shoulder can show abnormalities of the bone, labrum, and joint capsule [56]. Standard plain films of the shoulder are usually all that is required radiographically in the preoperative evaluation [51]. Magnetic resonance imaging may be useful in difficult cases to augment the clinical assessment but typically is not necessary [51]. The thresholds defined in specific studies can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability, allowing for earlier detection of recurrent posterior instability [2].

Investigations

Plain radiography: At least two views are required for shoulder imaging: an anteroposterior view in the plane of the glenoid and an axillary projection with the arm in abduction to demonstrate the relationship of the humeral head to the glenoid [91]. The axillary view is necessary for evaluating glenohumeral joint instability and determining humeral head position within the glenoid fossa [101]. This view may detect occult, locked posterior shoulder dislocation in patients exhibiting a lack of passive external rotation [101]. The standardized 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]. The axillary truth view can show posterior subluxation or "functional decentering" that is not evident in images taken with the arm at the side [43]. Standardized plain films are almost always sufficient to garner the information needed for shoulder evaluation [43]. Radiography can be used for screening patients for significant glenoid bone loss [167]. However, radiographs seem inferior to CT scans for assessing osseous lesions, especially at the glenoid rim [166].

CT: 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 [101]. 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]. There is significant heterogeneity in both the imaging modality and method used to measure glenoid bone loss in clinical studies [175].

MRI: MRI is useful to identify labral tears and rotator cuff tears, although the accuracy for these is enhanced by combining the scan with arthrography [91]. MR arthrography (MRA) increases both sensitivity and specificity in detecting injuries to the capsuloligamentous complex compared to traditional MRI [96]. In a meta-analysis of 4,667 shoulders, MRA had a sensitivity of 88% and specificity of 93% for detecting glenoid labral lesions, compared to MRI sensitivity of 76% and specificity of 87% [96]. MR arthrography is considered the benchmark for evaluation of labral tears [98]. The presence of glenoid dysplasia, increased capsular cross-sectional area, and increased glenoid retroversion have been found to be associated with increased posterior labral tears and symptomatic instability [96]. 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 [96]. Regardless of the radiologist interpretation of MRA, patients with symptomatic posterior shoulder instability do benefit from arthroscopic stabilization surgery [41]. The study investigated and compared morphological factors on magnetic resonance imaging between pain-predominant and apprehension-dominant instability presentations [174].

Ultrasound: Ultrasonography is a simple and accurate test for identifying rotator cuff tears and calcific tendinitis [91]. It serves as a low-cost alternative to MRI and arthrography for evaluating both skeletal and soft-tissue structures of the shoulder [98]. Ultrasonography can provide immediate, real-time visualization of the rotator cuff, biceps tendon, and calcific deposits [98]. 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 [98].

Other Considerations: Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays [6].

Treatment

Non-Operative

NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder [62]. There was no evidence regarding the effectiveness of surgical management for post-traumatic chronic shoulder instability [16].

Operative

Indications: Lafosse et al. consider cases of recurrent posttraumatic posterior instability, the presence of humeral and/or glenoid defects, and cases of demonstrable non-voluntary instability with glenoid dysplasia or hypermobility as indications for a posterior bone block [59].

Surgical Approach / Technique: Arthroscopic surgical techniques have facilitated successful management of both recurrent posterior subluxations and frank posterior instability [20]. The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising [4]. Good long-term results with improvement in stability, pain, and function can be obtained with posterior inferior capsular shift [71]. A "pinch-and-tuck" arthroscopic technique for capsular plication effectively and safely addresses capsular laxity in patients with posterior shoulder instability [34]. An arthroscopic technique for posterior labral repair in the beach-chair position maintains the principles of anatomic restoration and reliable fixation while expanding the practical applicability of the beach-chair position for posterior shoulder instability [18].

Bone Block Augmentation: Both glenoid osteotomy and bone block procedures can successfully address symptomatic posterior shoulder instability [130]. 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 [129]. However, there is a moderate rate of recurrence following posterior bone block for posterior shoulder instability [15].

Other Considerations: In a cadaveric model, an isolated reverse Bankart repair with a glenoid defect ≥20% is not sufficient to restore glenohumeral stability [59]. In a group of 75 patients who underwent arthroscopic capsulolabral repair with a minimum follow-up of 24 months, a bone defect of 11% increased the risk of failure by 10.4 times, while a 15% defect increased it 24.4 times [59]. Di Giacomo et al. propose a glenoid defect ≥20% as the cut-off for posterior bone block techniques [59].

Complications

Recurrence and Failure

Arthroscopic stabilization of posterior shoulder instability yields low rates of recurrent instability, revisions, and residual pain [17]. However, failure of primary stabilization procedures is often related to uncorrected anatomic pathology [28]. Recurrence is reliably linked to either a failure to address a glenohumeral stabilizer during the primary procedure or the development of a new lesion in these structures [33]. Relevant lesions contributing to recurrence include glenoid fossa deficiency or malpositioning, posterior labral tearing or attenuation, and laxity within anterior or posterior capsuloligamentous structures [33]. Additional contributors to posterior instability include glenoid retroversion, glenoid dysplasia, posterior glenoid bone defects, dynamic glenoid malpositioning from lost scapular mechanics, and loss of compressive forces on the humeral head [33]. When considering glenoid osteotomy for posterior instability, the high rate of persistent instability must be factored into treatment decisions [195]. One study reported a high failure rate in both cohorts, with 19 out of 33 shoulders (58%) experiencing structural failure such as recurrent dislocation or revision surgery [186]. In two of three patients with unsatisfactory results following Bankart repair using the STATAK device, incomplete anchoring appeared to cause postoperative subluxation [178].

Bony and Hardware Complications

Neurovascular structures at risk during glenoid bone augmentation include the musculocutaneous, axillary, and suprascapular nerves [161]. Potential complications of this procedure also include graft non-union with bent or broken screws, osteolysis or reabsorption of proximal grafts with prominent hardware, decreased range of motion, and long-term degenerative changes or osteoarthritis [161]. Following the modified Bristow procedure, arthrosis was observed in 4 patients and non-union occurred in 10 patients [196]. Recurrence of instability is significantly more frequent when bone union fails after arthroscopic bony Bankart repair [193]. In contrast, the second-generation arthroscopic anatomic glenoid reconstruction group demonstrated a lower rate of hardware complications, with no patients requiring revision surgery for hardware removal [194].

General Surgical Complications

Coracoid transfers for shoulder instability are challenging procedures associated with a broad range and significant incidence of complications [27]. Conversely, arthroscopic management of posterior-inferior shoulder instability carries a minimal complication profile [7]. Following Latarjet-Bristow procedures, the early graft failure rate is 4.7% and the nerve injury rate is 3.2% [162]. Two-thirds of graft failures following these procedures required reoperation [162], while half of the nerve injuries required reoperation [162]. Complications reported after arthroscopic revision Bankart repair include transient sensory brachial plexopathy due to interscalene anesthesia, delayed wound healing, frozen shoulder, and acute postoperative infection [164]. The overall complication rate for arthroscopic acute acromioclavicular dislocation fixation is 22.4% [179].

Recovery

Rehabilitation protocol: Initial management for microtraumatic posterior shoulder instability is rehabilitation [35]. The Watson Posterior Instability Program, undertaken over 24 weeks, has demonstrated significant improvements in patient-reported outcome measures at 12 weeks [35]. For scapular dyskinesis and SICK syndrome secondary to chronic type III acromioclavicular dislocation, a rehabilitation protocol yields positive improvements in shoulder function within 6 weeks [141]; however, patients who do not respond to this programme will not improve with extended rehabilitation time [141]. Following arthroscopic repair of the glenoid labrum, shoulder immobilisation for at least 3 weeks and an early start of physiotherapy are important factors for good functional results [132]. Postoperative scapular dyskinesis after a Latarjet procedure typically resolves with 6 months of a specific rehabilitation protocol, as observed in four out of five cases [143].

Functional milestones: Arthroscopic stabilization of posterior shoulder instability results in good outcomes with high patient satisfaction and low rates of recurrent instability, revisions, and residual pain [17]. Good long-term results, including improvements in stability, pain, and function, can be obtained following posterior inferior capsular shift [71]. In collision sports athletes, arthroscopic posterior Bankart repair for traumatic posterior shoulder instability results in clinically meaningful improvement [168].

Other Considerations: Systematic review data demonstrate high rates of return to sport and relatively high rates of return to preinjury level of sport among athletes who underwent surgical treatment for posterior shoulder instability [69]. Arthroscopic posterior Bankart repair for traumatic posterior shoulder instability in collision sports athletes resulted in a high return-to-play rate [168]. Arthroscopic stabilization procedures can be applied as the primary treatment of recurrent anterior shoulder instability with a large glenoid bone erosion for functional restoration and return to previous sports activity level [146]. The Congruent arc Latarjet procedure is associated with a high percentage of return to sport after a minimum follow-up of 10 years [172]. Regarding recurrence and complications, arthroscopic posterior Bankart repair for traumatic posterior shoulder instability in collision sports athletes resulted in a low recurrence rate [168]. The Congruent arc Latarjet procedure is associated with a low rate of recurrences after a minimum follow-up of 10 years [172]. 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 [27]. Early results suggest that arthroscopic coracoid transfer is a technically feasible procedure that is able to restore shoulder stability [58]. Thresholds defined in a 2025 study can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability, allowing for earlier detection of recurrent posterior instability [2].

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)
• [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. [2] (10.1016/j.jseint.2025.08.006)
• [L4] At a minimum of 2 years successful correction of scapular anatomy can improve static subluxation and restore subjective and objective shoulder stability. [3] (10.1016/j.jseint.2025.06.018)
• [L1] The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising. [4] (10.1016/j.arthro.2014.11.009)
• [L5] Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays. [6] (10.5435/00124635-200608000-00004)
• [L4] Arthroscopic management of posterior-inferior shoulder instability has a successful track record and minimal complication profile. [7] (10.1016/j.arthro.2018.06.057)
• [L5] The entity should be considered when patients who exhibit posterior shoulder pain or instability after a traumatic event are evaluated. [8] (10.1016/s1058-2746(95)80024-7)
• [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. [9] (10.1016/j.arthro.2021.07.018)
• [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. [11] (10.2106/jbjs.rvw.23.00243)
• [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. [15] (10.1016/j.jse.2021.06.013)
• [L1] There was no evidence regarding the effectiveness of surgical management for post-traumatic chronic shoulder instability. [16] (10.1136/bjsports-2017-098539)
• [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)
• [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. [21] (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. [22] (10.1177/03635465261421534)
• [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. [24] (10.1016/j.asmr.2020.08.007)
• [L5] [26] (10.1016/j.xrrt.2026.100861)
• [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. [27] (10.1016/j.jse.2012.02.008)
• [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. [28] (10.1016/j.arthro.2010.11.057)
• [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. [30] (10.5435/jaaos-d-15-00631)
• [L3] Patients do not always recognize anterior shoulder instability, and initial physical examination may be limited in the acute setting. [32] (10.1177/23259671251414851)
• [L4] [33] (10.1016/j.jse.2012.11.019)
• [L5] The article presents an alternative technique for capsular plication that effectively and safely addresses capsular laxity in patients with posterior shoulder instability. [34] (10.1016/j.eats.2025.103794)
• [L4] [35] (10.1016/j.jseint.2024.09.016)
• [L5] [37] (10.1530/eor-24-0025)
• [L3] Regardless of the radiologist interpretation of MRA, patients with symptomatic posterior shoulder instability do benefit from arthroscopic stabilization surgery. [41] (10.1016/j.xrrt.2026.100675)
• [L4] [47] (10.1016/j.arthro.2011.06.015)
• [L4] [48] (10.2106/00004623-195638050-00001)
• [L4] [49] (10.1016/s1058-2746(98)90183-5)
• [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. [50] (10.1177/0363546518819199)
• [L3] [51] (10.1097/00132589-200001040-00009)
• [L5] In patients with suspected posterior glenohumeral instability, imaging of the affected shoulder can show abnormalities of the bone, labrum, and joint capsule. [56] (10.2214/ajr.07.3849)
• [L1] Early results suggest that arthroscopic coracoid transfer is a technically feasible procedure that is able to restore shoulder stability. [58] (10.1016/j.arthro.2012.11.022)
• [L5] [59] (10.1530/eor-22-0009)
• [L4] This patient-specific procedure addresses the underlying morphologic abnormality while preserving native glenoid anatomy. [61] (10.1016/j.xrrt.2026.100878)
• [L4] NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder. [62] (10.1177/23259671261440208)
• [L5] [65] (10.1097/00132589-200206000-00006)
• [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. [69] (10.1016/j.jseint.2020.08.002)
• [Paper] [70] (10.1097/00132589-200309000-00002)
• [L4] Good long term results can be obtained with improvement in stability, pain, and function. [71] (10.1016/s1058-2746(96)80104-2)
• [L5] Current glenoid bone loss measurements are unable to provide an adequate estimation on the actual biomechanical effect of glenoid defects because the relation between the glenoid defect size and its biomechanical effect is nonlinear and patients with shoulder instability have constitutional biomechanically relevant glenoid concavity shape differences. [110] (10.1177/0363546518819102)
• [L5] Glenoid as well as acromial malalignment alone is associated with pathological posterior translation of the humeral head across the glenoid upon simulated active elevation. [114] (10.1177/03635465251411312)
• [L5] Glenohumeral contact patterns highly depend on the amount of glenoid retroversion and posterior labral and/or bony glenoid integrity. [120] (10.1177/03635465251365497)
• [L5] The PPS injury produces alterations in GH kinematics with implications for GH joint instability, increased GH joint loading, and potential joint damage. [122] (10.1016/j.jse.2024.12.023)
• [L5] The acromion acts as a mechanical buttress to posterior humeral head displacement. [123] (10.1016/j.jse.2024.09.047)
• [L5] The long head of the biceps has a pertinent biomechanical role in glenohumeral stability regardless of the condition of the superior labrum. [124] (10.1016/j.arthro.2025.05.022)
• [L5] The presence of a large glenoid defect was associated with a 65% to 80% reduction in joint stability parameters. [126] (10.1097/bte.0000000000000151)
• [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. [129] (10.1016/j.eats.2023.05.023)
• [L1] Both glenoid osteotomy and bone block procedures can successfully address symptomatic posterior shoulder instability. [130] (10.1016/j.xrrt.2025.03.004)
• [L4] Shoulder immobilisation for at least 3 weeks on the one hand, and an early start of physiotherapy on the other are important factors for good functional results. [132] (10.1016/s1058-2746(96)80380-6)
• [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. [133] (10.1186/s12891-026-09537-y)
• [L3] Patients with C1 shoulders differ from healthy controls regarding osseous scapular and humeral morphology, scapulothoracic orientation, and shoulder girdle muscle distribution. [134] (10.1177/03635465241233706)
• [L5] [136] (10.5435/jaaos-d-19-00535)
• [L4] [140] (10.5435/jaaos-d-17-00056)
• [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. [141] (10.1007/s00167-014-2844-5)
• [L3] Four/5 resolved with 6 months of specific rehabilitation protocol. [143] (10.1016/j.jseint.2025.101510)
• [L3] Arthroscopic stabilization procedures can be applied as the primary treatment of recurrent anterior shoulder instability with a large glenoid bone erosion for functional restoration and return to previous sports activity level. [146] (10.1016/j.arthro.2018.03.009)
• [L4] [147] (10.1016/j.jisako.2025.101015)
• [L5] [161] (10.1136/jisakos-2019-000413)
• [L4] [162] (10.1016/j.arthro.2021.01.061)
• [L1] [164] (10.1016/j.arthro.2022.03.030)
• [L3] Radiographs seem inferior to CT scans for assessing osseous lesions especially at the glenoid rim. [166] (10.1016/j.jse.2013.04.020)
• [L4] Radiography can be used for screening patients for significant glenoid bone loss. [167] (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. [168] (10.1016/j.asmr.2025.101264)
• [L3] The Congruent arc Latarjet procedure is associated with a high percentage of return to sport, excellent functional outcomes and a low rate of recurrences after a minimum follow-up of 10 years. [172] (10.1016/j.jisako.2023.03.354)
• [L4] The study investigated and compared morphological factors on magnetic resonance imaging between pain-predominant (UPS) and apprehension-dominant (ASI) instability presentations. [174] (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. [175] (10.1302/0301-620x.104b1.bjj-2021-0751.r1)
• [L4] In two of the three patients with unsatisfactory results, incomplete anchoring of the device seemed to have caused subluxation after the operation. [178] (10.1016/1058-2746(93)90065-o)
• [L4] While many complications do not directly affect daily activities, they significantly affect the return to sports, with an overall complication rate of 22.4%. [179] (10.1016/j.otsr.2015.09.012)
• [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. [186] (10.1016/j.jseint.2026.101773)
• [L3] Recurrence of instability was significantly more frequent when bone union failed. [193] (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. [194] (10.1016/j.jisako.2025.100773)
• [L4] However, the high rate of persistent instability should be considered when making treatment decisions. [195] (10.1177/17585732211056053)
• [L4] Arthrosis of the shoulder joint was seen in 4 patients and non-union occurred in 10 patients. [196] (10.1016/s1058-2746(96)80120-0)

See Also

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

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