Up-to-date concepts and procedures in shoulder instability: a comprehensive review

Epidemiology

The incidence of anterior shoulder dislocations is reported between 23.9 and 26.9 per 100,000 person-years, with the highest rates among males aged 20–29 years [8]. Epidemiologic studies have consistently demonstrated that the risk of recurrence after a first-time dislocation exceeds 70% in individuals younger than 22 years who engage in contact or overhead sports [2,9]. Risk factors for recurrent instability include male sex, younger age, generalized ligamentous laxity, participation in collision or overhead sports, and bony defects at the time of initial dislocation [10]. Military populations, contact athletes, and manual laborers represent particularly vulnerable groups, in whom delayed surgical intervention after a dislocation often leads to suboptimal outcomes [11]. These demographic factors underscore the importance of early risk stratification and support operative management in selected patients, even after an initial episode of instability [11,12].

Clinical Significance

Beyond the immediate functional impairment associated with recurrent shoulder instability, repetitive dislocation episodes are associated with cumulative damage to both soft tissue and osseous structures of the glenohumeral joint [3,13]. Progressive erosion of the anterior glenoid rim and enlargement of the Hill-Sachs lesion significantly increase the complexity of surgical management and reduce the likelihood of successful soft-tissue stabilization [14]. Moreover, recurrent instability is a recognized risk factor for the development of glenohumeral arthrosis. Hovelius and Rahme [15] demonstrated that more than 20% of patients who experienced recurrent dislocations eventually developed radiographic signs of arthritis over long-term follow-up . Thus, preventing recurrence—especially following the first instability episode—is critical, both for restoring shoulder function and maintaining long-term joint health [16].

Importance of Considering Bone Loss

Historically, bone loss was not considered a major factor in the treatment of shoulder instability, with surgical decision-making primarily based on the presence of a Bankart lesion [17]. However, the landmark study by Burkhart and De Beer [4] significantly altered this view by showing that patients with substantial glenoid bone loss (20%–25%) or Hill-Sachs lesions had markedly high failure rates after isolated Bankart repair .

Quantification of glenoid bone loss has since become a cornerstone of instability management. Studies employing three-dimensional computed tomography (3D CT) reconstructions have shown that glenoid defects exceeding as low as 13.5%–15% of the glenoid width markedly reduce shoulder stability and substantially increase the risk of failure after Bankart repair [18,19]. Furthermore, the concept of bipolar bone loss—recognizing the additive destabilizing effects of simultaneous glenoid and humeral head defects—has become crucial in refining patient selection for bone augmentation procedures. Initially introduced by Burkhart and De Beer, bipolar lesions were classified as "engaging" when the humeral head defect, or Hill-Sachs lesion, contacts the anterior glenoid rim during abduction and external rotation (Fig. 1.). Recent refinements have developed this qualitative assessment into a more precise, quantitative evaluation based on the "glenoid track" concept, significantly improving surgical decision-making [5,20].

Fig. 1.

Bipolar bone loss of the shoulder. (A) Axial computed tomography image demonstrating anterior glenoid bone loss (blue arrow). (B) Arthroscopic view confirming glenoid bone loss and corresponding cartilage defects. (C) Arthroscopic visualization of a Hill-Sachs lesion on the humeral head.

The glenoid track concept, proposed by Yamamoto et al. [7], further advanced this understanding by introducing a biomechanical model that predicts the likelihood of a Hill-Sachs lesion engaging with the glenoid rim . The glenoid track represents the contact area between the glenoid and humeral head during shoulder movement. Under normal conditions, the glenoid track width is approximately 83% of the glenoid width. When there is anterior glenoid bone loss, this effectively narrows the glenoid track. If a Hill-Sachs lesion remains within the glenoid track boundaries, it is considered "on-track," indicating stable intrinsic support. Conversely, lesions that extend medially beyond the narrowed glenoid track are "off-track," indicating insufficient bone support and a higher risk of recurrent instability. Off-track lesions, where the Hill-Sachs defect extends medially to the glenoid track, are major predictors of failure following soft-tissue-only repair [5,7].

How Much Bone Loss Is Critical? Revisiting Subcritical Bone Loss

The traditional concept of “critical bone loss” posited that defects exceeding 20%–25% of the glenoid surface warranted bone augmentation procedures [4]. However, emerging biomechanical and clinical evidence has challenged this threshold. Shaha et al. [21] demonstrated that even defects as small as 13.5% negatively impact shoulder stability and functional outcomes after Bankart repair. In addition, they highlighted that subcritical bone loss, defined as glenoid loss between 13.5% and 20%, is associated with substantially worse Western Ontario Shoulder Instability scores postoperatively compared to patients without significant bone defects.

Cadaveric biomechanical studies have further revealed that small glenoid defects (2 mm or 7.5%) critically impair the concavity-compression mechanism, where rotator cuff muscles compress the humeral head into the concave glenoid fossa to maintain joint stability, particularly during mid-range shoulder motion [22]. As a result, increasing emphasis is placed on quantifying even moderate defects and tailoring the surgical strategy accordingly. This nuanced understanding has fueled the movement toward earlier consideration of bone-block procedures, even in cases previously deemed suitable for isolated soft-tissue repair.

Bone Stock and Concavity are Impactful

Recent research has revealed that shoulder stability is not dictated solely by glenoid surface area but also by the depth of the glenoid concavity. Yamamoto et al. [23] showed that flattening of the glenoid, even without substantial surface loss, impairs the ability of the glenoid to resist translational forces. Moroder et al. [24] further introduced the “concavity index” to quantitatively assess glenoid integrity by calculating the ratio between the depth of the glenoid concavity and its diameter, measured on axial computed tomography images perpendicular to the glenoid's long axis at the level of the inferior glenoid circle [25]. This method has enhanced accuracy in evaluating glenoid concavity, assisting surgeons in determining optimal surgical strategies [24].

Shoulders with a shallow or flattened glenoid exhibit reduced resistance to humeral head translation and are predisposed to failure after isolated Bankart repair. Consequently, assessment of the glenoid curvature and morphology now supplements bone loss measurement in preoperative evaluation algorithms [25,26].

First-Time Dislocators: Operate or Observe?

The management of patients with a first-time anterior shoulder dislocation remains a subject of ongoing debate. Traditional nonoperative management, particularly in the general population, resulted in acceptable outcomes with low recurrence risk. However, among young athletes and military personnel, nonoperative treatment frequently results in unacceptable rates of recurrent instability and poorer functional outcomes [27,28]. In a prospective randomized controlled trial, Bottoni et al. [11] found that early surgical stabilization significantly reduced recurrence rates in young athletes, with only 11.1% of operatively treated patients experiencing recurrent instability compared to 75% in the nonoperative group. Hu et al. [29] corroborated these findings, reporting superior outcomes following early arthroscopic stabilization compared to conservative management, including significantly higher return-to-sport rates (83.5% vs. 66.0%) and lower rates of re-dislocation (7.5% vs. 53.0%), subluxation (3.1% vs. 24.2%), and need for subsequent surgery (5.6% vs. 37.8%). These studies advocate for a more aggressive surgical approach in first-time dislocators who possess high-risk features such as participation in contact sports, presence of bone loss, and high Instability Severity Index Score (ISIS) (Table 1) [6].

Table 1.

Instability severity index score

Recurrent Dislocators: Latarjet versus Bankart Repair?

Arthroscopic Bankart repair has shown favorable outcomes even in cases of recurrent dislocation when risk factors are absent, such as minimal bone loss and non-contact athletic activity [30,31]. However, its success rate significantly declines in the presence of high-risk features, including glenoid bone loss greater than 15%, off-track Hill-Sachs lesions, or participation in collision sports. Historically, the Latarjet procedure was reserved for revision cases or those of severe bone loss. However, accumulating data suggest that, in high-risk patients—particularly young male contact athletes with glenoid bone loss or off-track lesions—primary Latarjet procedures achieve superior outcomes compared to Bankart repair [32,33].

Zimmermann et al. [32] reported lower recurrence rates, faster return to sport, and higher patient satisfaction in primary Latarjet compared to arthroscopic Bankart repair in contact athletes. Furthermore, the triple-block effect of the Latarjet procedure—comprising the bone graft, the sling effect of the conjoint tendon, and capsular repair—provides robust stability even in the presence of moderate bone loss [34].

Consequently, many surgeons recommend a more liberal use of the Latarjet procedure in high-risk primary instability patients, particularly when preoperative imaging reveals significant bipolar bone loss (e.g., combined glenoid bone loss exceeding 13.5%–15% accompanied by an engaging, off-track Hill-Sachs lesion), or when the ISIS score exceeds 6 points [35].

Shoulder Pacemaker: Neuromodulation for Instability

Recent studies have introduced the concept of a "shoulder pacemaker," utilizing neuromuscular electrical stimulation to dynamically enhance shoulder stability [36]. Moroder et al. [36,37] demonstrated that targeted stimulation of the rotator cuff and periscapular muscles in patients with shoulder instability improved active joint stabilization . Although still experimental, this technique shows promise either as an adjunct to conventional surgical stabilization or, in select cases, as a potential nonoperative alternative. Current prototypes involve wearable neuromodulation devices programmed to detect risky shoulder positions and activate stabilizing muscles preemptively. Early-phase trials report improved subjective shoulder stability and reduced apprehension during provocative maneuvers [36].

Knotless versus Knotted Techniques in Soft-Tissue Repair

Advances in anchor technology have popularized knotless repair constructs in Bankart and remplissage procedures. Lacheta et al. [38] reported that knotless Bankart repairs demonstrated equivalent biomechanical strength to traditional knotted techniques while reducing surgical time and the risk of knot irritation [39].

Recent systematic reviews have reinforced these biomechanical findings with clinical evidence. A review of nine comparative studies (including two randomized controlled trials) involving 720 patients found no significant differences in functional outcomes, residual pain, or complication rates—including redislocation, subluxation, and revision surgery—between knotless and knotted repairs. While range of motion in external rotation and forward flexion was slightly more favorable in the knotless group, overall clinical results remained comparable [40]. Similarly, a 2024 meta-analysis incorporating nine studies and 729 patients concluded that the two techniques yielded equivalent results regarding recurrence, functional score improvement, and revision rates, with the only consistent advantage of knotless repair being a modest reduction in operative time. However, this time savings did not appear to confer a measurable clinical benefit. As such, current evidence supports the use of either technique, provided appropriate surgical principles are followed [41].

Moreover, knotless systems facilitate easier suture tensioning and may enable more substantial anatomic capsulolabral restoration. However, a meticulous technique is essential to prevent overtightening, which can lead to restricted external rotation and negatively affect functional outcomes [38].

Another New Option: Dynamic Anterior Stabilization

Dynamic Anterior Stabilization (DAS) represents an innovative alternative to traditional bone block procedures in patients with minimal to moderate bone loss but an engaging Hill-Sachs lesion [42]. Originally proposed by Collin and Lädermann [42], DAS utilizes a transfer of the long head of the biceps tendon through a subscapularis split to create a dynamic anterior restraint.

The most suitable indications for DAS are anteroinferior glenohumeral instability with limited bone defects (<20%), particularly when a Hill-Sachs lesion is present, but the overall glenoid bone loss does not warrant a full bone block procedure. DAS may be especially beneficial in cases aiming to preserve the coracoid process or when minimizing surgical invasiveness.

Early clinical outcomes demonstrate comparable stability and functional recovery to traditional Latarjet procedures, with the added benefits of preserving coracoid anatomy and minimizing graft-related complications [42,43]. In a prospective study of patients with anterior instability and up to 20% glenoid bone loss, 93% returned to sports, and only one recurrence (6.7%) was reported, with no major complications in any area [43]. These findings support DAS as a safe and effective alternative to traditional bone block procedures, while preserving native anatomy and avoiding graft-related risks. However, larger multicenter studies with long-term follow-up are needed to validate these promising initial results.

All-Arthroscopic Latarjet

The evolution of arthroscopic Latarjet techniques has significantly reduced the morbidity traditionally associated with the open procedure [44]. Fully arthroscopic approaches allow improved visualization, smaller incisions, and preservation of the deltopectoral interval. Hurley et al. [44] demonstrated similar stability outcomes between arthroscopic and open Latarjet procedures, with earlier return of motion and reduced soft-tissue disruption in the arthroscopic cohort. Nevertheless, the technical complexity remains high, with steep learning curves and increased operative times during early surgeon experience .

Less is More: Screw versus Suture-Button Fixation in the Latarjet

Fixation during coracoid transfer has traditionally involved two screws. However, suture-button constructs have emerged as a viable alternative to minimize hardware-related complications such as screw loosening, graft fracture, or prominence [45]. Recent biomechanical studies have shown that suture-button constructs provide similar fixation strength to traditional screws [45]. Additionally, early clinical outcomes suggest comparable functional scores and range of motion between the two techniques, while suture-button fixation demonstrates a lower rate of graft resorption (10.1%–18.5%) compared to screw fixation (25.2%–47.6%), as well as fewer hardware-related complications and reoperations [45]. In addition, techniques involving all-suture cerclage fixation without the use of a button are now reported [46]. Ongoing long-term follow-up studies will determine if these early advantages translate into superior durability over time.

An overview of the Bankart and Latarjet procedures for anterior shoulder instability is presented in Table 2.

Table 2.

Comparison of Bankart repair and the Latarjet procedure for anterior shoulder instability

Free Bone Block Procedures: Eden-Hybinette and Variants

The Eden-Hybinette procedure, now commonly referred to as “free bone block augmentation” or “anatomic glenoid reconstruction” as opposed to the Latarjet, has gained renewed interest, particularly for revision cases or when the coracoid is inadequate [47]. This technique uses an autologous iliac crest bone graft to restore the glenoid arc. Gilat et al. [47] demonstrated excellent outcomes in shoulder stability, with graft union rates exceeding 90%.

Free bone block procedures allow customizable graft size and positioning and are versatile for extensive or irregular glenoid defects. However, they carry risks of graft resorption, donor site morbidity, and technical complexity [47]. A key consideration in free bone block reconstruction is the choice between autograft and allograft sources. Provencher et al. [48] reported that distal tibial allografts closely match the native glenoid curvature and represent a viable alternative to iliac crest autografts, particularly for patients wishing to avoid donor site morbidity. Yet, a fresh frozen distal tibia allograft is not available in most parts of the world. Allografts eliminate the need for autologous harvest but are associated with risks of disease transmission, immune reaction, and potentially delayed union. Autografts provide superior biologic integration but at the cost of additional surgical sites and increased pain [48].

In a comparative study of four augmentation techniques (allograft/autograft bone block, open/arthroscopic Latarjet), the allograft group demonstrated the lowest healing rate (20%), with osteolysis in 100% of cases and significantly reduced glenoid surface area at one-year follow-up (P<0.001). In contrast, autograft, open Latarjet, and arthroscopic Latarjet groups achieved healing rates of 80%–90%, with far lower rates of resorption and no cases of osteolysis in the arthroscopic Latarjet group [49].

Thus, graft selection should be tailored by patient, considering anatomical requirements, biological healing potential, and tolerance for donor-site morbidity. In cases where reliable graft incorporation is essential, such as in high-demand patients or revision surgeries, autografts may provide better long-term outcomes.

Patient-Specific Partial Glenoid Arthroplasty

A cutting-edge, experimental treatment involves custom 3D-printed patient-specific partial glenoid arthroplasty for large isolated glenoid defects (Fig. 2). Although this method is still in its infancy, pilot feasibility studies report promising biomechanical restoration of the glenoid contour and joint congruency. Limitations include cost, implant integration uncertainty, and the need for highly specialized imaging and manufacturing infrastructure [50].

Fig. 2.

Cadaveric three-dimensional-printed partial glenoid arthroplasty. (A) Insertion of the three-dimensional (3D)-printed partial glenoid component through the anterior portal. (B) The glenoid component fixed to match the contour of the anterior glenoid bone defect. (C) Anterior labral repair performed over the fixed glenoid component. (D) The 3D-printed glenoid component precisely aligned with the glenoid bone defect contour.

Biologics to Enhance Healing

The use of biologic adjuncts such as platelet-rich plasma and mesenchymal stem cells in shoulder instability surgery remains investigational but highly promising [51,52]. Azharuddin et al. [51] highlighted the use of biologic augmentation to enhance capsulolabral healing and graft incorporation, particularly in revision settings or patients with poor tissue quality . Future large-scale randomized controlled trials are needed to confirm clinical efficacy and optimize delivery protocols.

Artificial Intelligence in Surgical Planning and Risk Prediction

Artificial intelligence (AI) is poised to revolutionize orthopedic surgery, including shoulder instability management [53]. Machine learning algorithms are being developed to predict recurrence risk based on imaging and clinical parameters [53], automate bone loss quantification and glenoid track assessments, and guide surgical planning by simulating procedural outcomes. Lu et al. [54] emphasized that AI-assisted tools could lead to more precise, patient-specific interventions, minimizing recurrence and maximizing functional recovery. However, challenges remain regarding data standardization, validation, and ethical considerations regarding autonomous decision-making.