Management of Recurrent Anterior Shoulder Instability: A Therapeutic Algorithm Based on Bipolar Bone Loss

Giovanni Di Giacomo, MD, ITALY Gianmarco Marcello, MD, ITALY Philipp Moroder, MD, SWITZERLAND Matthew T. Provencher, MD, UNITED STATES

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Introduction

In a healthy shoulder, the capsuloligamentous structures serve as the primary stabilizers at the extreme ranges of motion, where part of the shoulder capsule becomes taut. In contrast, during the mid-range of motion, the capsule is more relaxed, and the joint’s stability is predominantly maintained by the combined action of negative intra-articular pressure and the concavity-compression mechanism (dynamic compression of the convex humeral head into the glenoid concavity, provided mainly by the rotator cuff muscles). The presence of anterior glenoid bone loss compromises joint stability by reducing the glenoid depth, the arc length, articular curvature, and the total articular surface. This loss leads to diminished contact pressures in the posterosuperior quadrant and increased pressures in the anteroinferior quadrant. As a result, there is a proportional reduction in the maximum force required to dislocate the shoulder. According to Greis et al., a 20% defect in the glenoid significantly increases the mean contact pressure in the anteroinferior quadrant, more than doubling this pressure in comparison with normal values.[1] Thus, even isolated glenoid bone loss can induce instability in the mid-range of motion. This explains why repairing only the capsulolabral structures, without addressing significant bone loss, often leads to treatment failure. At the extreme ranges of motion, the interaction between glenoid and humeral bone loss (as seen in Hill-Sachs lesions) plays a pivotal role in recurrent dislocations following Bankart repair. When the glenoid approaches the posterolateral region of the humeral head, a Hill-Sachs lesion, if it falls outside the coverage of the glenoid, may engage the anterior rim of the glenoid, thus contributing to instability. A Hill-Sachs lesion that does not cause instability in the presence of a preserved glenoid may, however, lead to instability if significant glenoid bone loss is present. Therefore, instability at the extremes of motion is influenced not only by the size, shape, and location of the Hill-Sachs lesion but also by the degree of glenoid bone loss, leading to what is referred to as bipolar bone loss.

The Glenoid Track Concept

Accurate evaluation of bipolar bone loss is essential for the management of shoulder instability, as it plays a critical role in predicting the outcomes of stabilization procedures. To assess bipolar bone loss and predict the potential for Hill-Sachs lesion engagement, the concept of the glenoid track proves useful. This concept aids in the decision-making process by providing a clearer framework for addressing recurrent anterior shoulder instability (Figure 1).

Fig. 1 A drawing representing the en face view of the glenoid and the posterior view of the humeral head in a right shoulder. The glenoid track area is is differentiated into the central track and the peripheral track (with the latter being the medial one-fourth of the glenoid track). A central-track Hill-Sachs lesion is shown on the posterosuperior surface of the humeral head. GW = glenoid width, d = defect, HSI = Hill-Sachs interval, HSL = Hill-Sachs lesion.

Bone defects should be assessed in conjunction with other risk factors for persistent instability, including the patient’s age, sex, shoulder hyperlaxity, and participation in high-contact or overhead sports. These factors collectively enhance the precision of estimating the likelihood of recurrence.

The Glenoid Track Instability Management (GTIM) score has been introduced as a tool to guide the selection of treatment, such as deciding between bone-grafting procedures (e.g., the Latarjet technique) and arthroscopic options (e.g., Bankart repair). This scoring system integrates multiple risk factors, such as the patient’s age at the time of surgery, the type and intensity of sport participation, and shoulder hyperlaxity, alongside the glenoid track concept.[2]

Management Algorithm Based onthe GTIM score

Currently, a variety of techniques are available for the management of anterior shoulder instability, and these techniques can be organized into an algorithm that outlines their specific indications and guides therapeutic choices (Figure 2).

Fig. 2 A flowchart depicting the proposed algorithm, based on bipolar bone loss, for the management of recurrent anterior shoulder instability. GTIMS = Glenoid Track Instability Management Score, ASA = arthroscopic subscapularis augmentation, GBL = glenoid bone loss, HSL = Hill-Sachs lesion.

For patients with a GTIM score of <4, a soft-tissue procedure such as the Bankart repair may be sufficient. In certain cases, however, the Bankart repair alone may not offer adequate stabilization. For those patients, another procedure, such as remplissage, arthroscopic subscapularis augmentation (ASA), or bone block, may be necessary in addition to the Bankart repair, depending on the patient's specific characteristics and the extent of bone loss. Remplissage is particularly indicated in cases of recurrent instability or peripheral-track Hill-Sachs lesions, whereas ASA is beneficial for patients with constitutional hyperlaxity, and bone-block procedures are appropriate for patients with subcritical glenoid bone loss.

Patients with a GTIM score of ≥4 should be managed with the Latarjet procedure, which is typically reserved for high-risk individuals, severe bone loss, insufficient capsular tissue, or revision following failed surgery. This technique is well-established as a reliable solution, with favorable outcomes and high rates of return to sport.

However, the treatment approach for these patients can vary globally, depending on the surgeon’s preferences and the specific nature of the patient’s condition.

Patients with a GTIM score of ≥4 can be divided into two categories: (1) those with significant bone loss (off-track Hill-Sachs lesions) and (2) those with high-risk factors unrelated to bone loss.

For patients with off-track Hill-Sachs lesions, the Latarjet procedure is generally recommended, although some surgeons may opt for addressing the bone loss with a capsulolabral repair combined with a bone block and remplissage, which restores translation and stiffness closer to that of a native glenohumeral joint. In such cases, the Latarjet procedure may be reserved for revision surgery.

A key question remains whether the Latarjet technique can reliably convert all off-track Hill-Sachs lesions into on-track lesions. Preoperative measurements of the glenoid track and the size of the coracoid process are advised, as a Hill-Sachs interval that is >7.45 mm wider than the glenoid track has been identified as a risk factor for residual postoperative off-track lesions.[3] In rare instances, additional procedures such as bone-grafting of the Hill-Sachs lesion or remplissage may be considered alongside the Latarjet procedure, or, alternatively, larger bone-block procedures (e.g., iliac crest bone graft, distal tibial allograft, or the Eden-Hybbinette procedure) may be used, typically in the context of a glenoid revision.

The management of patients with a GTIM score of ≥4 but without significant bipolar bone loss remains a subject of ongoing debate. In such cases, where bone loss is minimal or absent, a variety of surgical approaches may be appropriate, with treatment decisions largely determined by individual patient factors and surgeon discretion. For instance, Merrill and Arciero stated that open Bankart repair is appropriate in the following circumstances: male athletes involved in collision sports (under 20 years old), those exhibiting 10-20% glenoid bone loss, individuals with a history of more than five dislocations, patients presenting with poor capsulolabral tissue quality, instability events occurring during daily activities or while sleeping, or in cases where a prior well-performed arthroscopic procedure has failed despite minimal bone loss. [4] Conversely, other surgeons may opt for a bone-block procedure combined with Bankart repair, or Bankart repair plus remplissage, depending on whether bone loss is more pronounced on the glenoid or humeral side. That is because these approaches, in certain cases, may yield clinical outcomes comparable with those of the Latarjet procedure, while reducing the risk of postoperative complications.

In cases involving 10%-20% glenoid bone loss, first-time dislocation occurring within the last 3 years, and <5 total dislocations, Taverna et al. favor arthroscopic bone block with Bankart repair. However, for patients experiencing >5 dislocations or a first dislocation occurring >3 years earlier, the Latarjet procedure is preferred.[5] Given the low failure rates and relatively rapid return to sport associated with the Latarjet procedure, some surgeons continue to use it even in the absence of significant bone loss.

Summary

While the glenoid track concept remains an essential tool for evaluating the risk of Hill-Sachs lesions in the context of glenoid bone loss, it does have limitations. Variability in the methods used to assess glenoid bone loss and the Hill-Sachs interval can lead to differing results, and the identification of the medial margin of the rotator cuff footprint can be challenging, with measurement variability depending on the rotator cuff insertion.

Moreover, the management of subcritical glenoid or humeral bone loss continues to be a contentious issue worldwide. The GTIM scoring system provides valuable guidance for treatment selection in the most common scenarios of anterior shoulder instability; however, it is important to recognize that treatment must be individualized, as numerous variables affect clinical decision-making. Thus, while a comprehensive treatment algorithm can be proposed, it must be flexible enough to accommodate the wide range of patient-specific factors that influence the choice of therapy.

References

1. Greis PE, Scuderi MG, Mohr A, Bachus KN, Burks RT. Glenohumeral articular contact areas and pressures following labral and osseous injury to the anteroinferior quadrant of the glenoid. Journal of Shoulder and Elbow Surgery. 2002 Sep;11(5):442–51.
2. Di Giacomo G, Peebles LA, Pugliese M, Dekker TJ, Golijanin P, Sanchez A, et al. Glenoid Track Instability Management Score: Radiographic Modification of the Instability Severity Index Score. Arthroscopy 2020;36(1):56-67.
3. Calvo E, Delgado C. Management of off-track Hill-Sachs lesions in anterior glenohumeral instability. Journal of Experimental Orthopaedics. 2023 Mar 21;10(1).
4. Merrill CA, Arciero R. Open Bankart repair: a reproducible technique. Oper Tech Sports Med 2019 Mar;27(1):42-8
5. Taverna E, D’Ambrosi R, Perfetti C, Garavaglia G. Arthroscopic Bone Graft Procedure for Anterior Inferior Glenohumeral Instability. Arthroscopy Techniques. 2014 Dec;3(6):e653–60.

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