Understanding Hill-Sachs Lesion Size in Bipolar Instability

Surgeons evaluating anterior shoulder instability frequently confront complex osseous defects. In particular, assessing Hill-Sachs lesion size has emerged as a fundamental determinant of surgical success. Historically, clinicians viewed humeral head compression fractures merely as secondary markers of prior dislocation events. However, contemporary biomechanical models demonstrate that humeral bone loss actively interacts with anterior glenoid attrition. Therefore, treating these injuries requires an integrated approach to bipolar bone loss. When a patient experiences an anterior glenohumeral dislocation, the posterolateral humeral head impacts the rigid anterior glenoid rim. Consequently, this impaction creates a bony defect that compromises dynamic joint stability. Orthopedic surgeons encounter this challenge frequently in young contact athletes. Furthermore, recurrent instability episodes progressively enlarge the defect, medializing the articular margin. As a result, the humeral head loses critical articular surface area during dynamic abduction and external rotation. Recent literature emphasizes that we cannot assess humeral defects in isolation. Instead, surgeons must evaluate the humeral defect relative to residual glenoid width. Understanding this interplay allows clinicians to identify patients at substantial risk of recurrent instability. Thus, measuring Hill-Sachs lesion size provides actionable insights that guide reconstructive procedures.

The Transition from Binary Engagement to the Glenoid Track

For decades, surgeons classified humeral head lesions through a simplistic binary framework of engaging or nonengaging defects. Clinicians defined an engaging lesion as one that parallelled and caught on the anterior glenoid rim during functional abduction and external rotation. However, this classical arthroscopic definition often created diagnostic confusion during preoperative planning. Consequently, investigators introduced the revolutionary glenoid track concept to quantify the dynamic zone of glenohumeral contact. In an intact shoulder, the glenoid track occupies approximately eighty-three percent of the glenoid diameter. Furthermore, when anterior glenoid bone loss occurs, the true contact track narrows by the exact width of that anterior defect. An on-track lesion remains entirely within this contact area throughout shoulder motion. Conversely, an off-track lesion extends medially beyond the remaining glenoid track. Therefore, off-track lesions lack bony support and easily engage the anterior rim, causing catastrophic recurrent dislocation. This paradigm shifted our clinical perspective from qualitative visual inspection to reproducible mathematical measurements. Nevertheless, recent investigations reveal that even binary on-track versus off-track distinctions may oversimplify joint mechanics. Indeed, the severity of instability exists along a biomechanical continuum rather than across a rigid threshold.

Distance to Dislocation and the Risk of Near-Track Lesions

To refine risk stratification beyond categorical track metrics, researchers developed the distance to dislocation concept. Clinicians calculate distance to dislocation by subtracting the Hill-Sachs interval from the remaining glenoid track width. Therefore, a negative numerical value corresponds to an off-track lesion, whereas a positive value represents an on-track lesion. However, focusing solely on this positive or negative sign ignores crucial biomechanical nuances. For example, a lesion situated mere millimeters from the medial track boundary behaves very differently from a purely lateral defect. Specialists term these borderline pathologies near-track lesions. Furthermore, clinical trials show that patients with near-track lesions carry significantly higher failure rates after isolated soft-tissue repair. As the distance to dislocation approaches zero, the safety margin against functional engagement rapidly disappears. In active athletes, physiological capsular laxity and high shear forces easily overcome this narrow margin. Consequently, relying on a binary on-track label can produce a false sense of security. Surgeons must instead examine the precise numerical distance to dislocation during preoperative workups. Moreover, tracking this value helps clinicians anticipate instability in shoulders with subcritical glenoid bone loss. Ultimately, distance to dislocation provides a granular, continuous assessment that transforms surgical decision-making.

Surgical Decision-Making: Beyond Isolated Bankart Repair

Historically, orthopedists treated anterior shoulder instability with isolated arthroscopic Bankart repair regardless of bone loss severity. However, substantial clinical evidence confirms that isolated labral repair yields unacceptable recurrence rates in patients with significant bipolar defects. Therefore, modern surgical algorithms aggressively integrate supplementary stabilization procedures. When encountering an off-track defect or a near-track lesion with limited distance to dislocation, surgeons frequently combine Bankart repair with an arthroscopic remplissage. During a remplissage, the surgeon fixes the infraspinatus tendon and posterior capsule directly into the Hill-Sachs crater. Consequently, this maneuver converts an intra-articular defect into an extra-articular structure, preventing humeral engagement against the anterior glenoid rim. In contrast, when anterior glenoid bone loss exceeds twenty to twenty-five percent, surgeons typically prefer bony reconstruction via the Latarjet procedure. Furthermore, recent data suggest that young contact athletes with near-track lesions benefit substantially from adding remplissage even to on-track lesions. This combined approach restores robust joint stability while preserving functional external rotation in most patients. In addition, tensionable knotless anchor constructs now make the remplissage procedure faster and highly reproducible. Ultimately, thoughtful surgical selection tailored to specific bone architecture protects patients from debilitating revision surgeries.

Preoperative 3D Imaging and Advanced Measurement Protocols

Accurate surgical planning relies on meticulous preoperative diagnostic imaging to quantify bipolar osseous defects. Currently, computed tomography with three-dimensional reconstruction represents the gold standard for evaluating glenoid bone loss and humeral head topography. Surgeons utilize three-dimensional CT to measure the en face glenoid surface area and calculate the precise Hill-Sachs interval. However, magnetic resonance imaging provides complementary visualization of critical soft-tissue structures, including the labrum and rotator cuff. In addition, advanced high-resolution MRI protocols can reliably calculate the glenoid track and distance to dislocation while sparing patients ionizing radiation. Nevertheless, studies highlight occasional interobserver variability between MRI-derived metrics and arthroscopic measurements. Therefore, clinicians must standardize their measurement methods across axial and three-dimensional multiplanar reconstructions. Specifically, radiologists and surgeons must measure the intact bony bridge between the rotator cuff footprint and the lateral margin of the lesion. Moreover, failing to account for this intact bridge can result in erroneous track calculations and inappropriate procedural choices. By combining advanced cross-sectional imaging with diligent physical examination, surgical teams accurately determine the exact biomechanical risk profile. Consequently, precise preoperative measurements pave the way for predictable and durable clinical outcomes.

Frequently Asked Questions

How does Hill-Sachs lesion size dictate the need for remplissage?

The overall size and medial extension of a Hill-Sachs defect directly determine whether the lesion will engage the anterior glenoid rim. When a lesion extends medially beyond the glenoid track or presents as a high-risk near-track defect, isolated Bankart repair carries unacceptable failure rates. Therefore, surgeons perform an arthroscopic remplissage to inset the infraspinatus tendon into the crater, effectively converting it into an extra-articular structure and neutralizing dynamic engagement during arm abduction.

What is the clinical significance of distance to dislocation in shoulder instability?

Distance to dislocation quantifies the exact numerical safety margin between the medial border of a Hill-Sachs lesion and the medial boundary of the glenoid track. Rather than relying on a rigid binary classification, this continuous measurement identifies vulnerable near-track lesions that sit dangerously close to engaging the anterior glenoid. Consequently, measuring distance to dislocation helps surgeons recognize at-risk patients who require supplementary procedural augmentation, such as remplissage, to prevent recurrent postoperative dislocations.

Why can an on-track lesion still fail after isolated Bankart repair?

Although an on-track lesion theoretically stays within the glenoid contact area, clinical failures still occur, particularly in competitive athletes with repetitive demands. Attenuated capsulolabral tissues, hyperlaxity, and high shear forces can easily overcome a narrow safety margin in near-track shoulders. Furthermore, recurring subluxations progressively deform soft tissues and enlarge humeral bone defects over time. As a result, relying strictly on an on-track diagnosis without considering patient-specific risk factors often leads to recurrent instability.

Disclaimer: This content is for informational and educational purposes only... Refer to the latest local and national guidelines for clinical practice.

References

1. Tramer JS et al. Editorial Commentary: Does Size Matter? Evaluating Hill-Sachs Lesion Size in Shoulder Instability. Arthroscopy. 2026 Sep 26. doi: 10.1002/arj.70654. PMID: 42798285.


2. Di Giacomo G, Itoi E, Burkhart SS. Evolving concept of bipolar bone loss and the Hill-Sachs lesion: from "engaging/non-engaging" lesion to "on-track/off-track" lesion. Arthroscopy. 2014;30(1):90-98.


3. Yamamoto N, Itoi E, Abe H, et al. Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: a new concept of subluxation. J Shoulder Elbow Surg. 2007;16(5):649-656.


4. Funakoshi T, Hartzler RU, Stewien E, Burkhart SS. Hill-Sachs Lesion Classification by the Glenoid Track Paradigm in Shoulder Instability: Poor Agreement Between 3-Dimensional Computed Tomographic and Arthroscopic Methods. Arthroscopy. 2019;35(6):1743-1749.