The role of bone in glenohumeral stability

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  • 1 Concordia Hospital for Special Surgery Rome, Italy
  • | 2 Università degli Studi di Roma La Sapienza, Dipartimento di Medicina Sperimentale, Trauma and Orthopaedics, Rome, Italy

M. Pugliese, Università degli Studi di Roma La Sapienza, Dipartimento di Medicina Sperimentale, Trauma and Orthopaedics, Piazzale Aldo Moro 5, 00185 Rome, Italy. Email: mattiapugliese@outlook.com
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  • Shoulder stability depends on several factors, either anatomical or functional. Anatomical factors can be further subclassified under soft tissue (shoulder capsule, glenoid rim, glenohumeral ligaments etc) and bony structures (glenoid cavity and humeral head).

  • Normal glenohumeral stability is maintained through factors mostly pertaining to the scapular side: glenoid version, depth and inclination, along with scapular dynamic positioning, can potentially cause decreased stability depending on the direction of said variables in the different planes. No significant factors in normal humeral anatomy seem to play a tangible role in affecting glenohumeral stability.

  • When the glenohumeral joint suffers an episode of acute dislocation, either anterior (more frequent) or posterior, bony lesions often develop on both sides: a compression fracture of the humeral head (or Hill–Sachs lesion) and a bone loss of the glenoid rim. Interaction of such lesions can determine ‘re-engagement’ and recurrence.

  • The concept of ‘glenoid track’ can help quantify an increased risk of recurrence: when the Hill–Sachs lesion engages the anterior glenoid rim, it is defined as ‘off-track’; if it does not, it is an ‘on-track’ lesion. The position of the Hill–Sachs lesion and the percentage of glenoid bone loss are critical factors in determining the likelihood of recurrent instability and in managing treatment.

  • In terms of posterior glenohumeral instability, the ‘gamma angle concept’ can help ascertain which lesions are prone to recurrence based on the sum of specific angles and millimetres of posterior glenoid bone loss, in a similar fashion to what happens in anterior shoulder instability.

Cite this article: EFORT Open Rev 2018;3:632-640. DOI: 10.1302/2058-5241.3.180028

Abstract

  • Shoulder stability depends on several factors, either anatomical or functional. Anatomical factors can be further subclassified under soft tissue (shoulder capsule, glenoid rim, glenohumeral ligaments etc) and bony structures (glenoid cavity and humeral head).

  • Normal glenohumeral stability is maintained through factors mostly pertaining to the scapular side: glenoid version, depth and inclination, along with scapular dynamic positioning, can potentially cause decreased stability depending on the direction of said variables in the different planes. No significant factors in normal humeral anatomy seem to play a tangible role in affecting glenohumeral stability.

  • When the glenohumeral joint suffers an episode of acute dislocation, either anterior (more frequent) or posterior, bony lesions often develop on both sides: a compression fracture of the humeral head (or Hill–Sachs lesion) and a bone loss of the glenoid rim. Interaction of such lesions can determine ‘re-engagement’ and recurrence.

  • The concept of ‘glenoid track’ can help quantify an increased risk of recurrence: when the Hill–Sachs lesion engages the anterior glenoid rim, it is defined as ‘off-track’; if it does not, it is an ‘on-track’ lesion. The position of the Hill–Sachs lesion and the percentage of glenoid bone loss are critical factors in determining the likelihood of recurrent instability and in managing treatment.

  • In terms of posterior glenohumeral instability, the ‘gamma angle concept’ can help ascertain which lesions are prone to recurrence based on the sum of specific angles and millimetres of posterior glenoid bone loss, in a similar fashion to what happens in anterior shoulder instability.

Cite this article: EFORT Open Rev 2018;3:632-640. DOI: 10.1302/2058-5241.3.180028

Anatomy and biomechanics

Glenohumeral stability is a multifactorial process whose balance is guaranteed by several structures, of which bone is one. The inherent discrepancy between the size of the humeral head and the scapular glenoid fossa1 allows for a wide range of motion (ROM), but demands effective stabilizers in order to avoid dislocation of the humeral head from its natural position in the glenoid cavity. Said stability is dependent on several anatomical and biomechanical factors: the relationship between the humeral head and the scapula in the different positions of the arm; the integrity of the bony structures and soft tissues; the static and dynamic neuromuscular balance of the muscles surrounding the joint.

Bone and soft tissue both interact to provide adequate stability at different ROMs. With the arm at rest, the weight of the arm hanging loose generates a negative static intra-articular pressure of around −30 mm Hg, which acts as the principal stabilizer of the glenohumeral joint, mainly preventing inferior dislocation.2,3 The long head of the biceps tendon,4 the rotator interval capsule and the coracohumeral ligament,5 located in an antero-superior position relative to the humeral head, add stability: the former by acting as a ‘rein’ to prevent humeral head migration in different directions (mainly antero-inferiorly), the latter by maintaining negative intra-articular pressure.

As the arm moves along the different planes, more factors come into play depending on the considered ROM, namely the mid-range and the end-range. Itoi et al6 defined the ‘end-range’ as the ROM performed when the arm comes to the limit of shoulder movement. By doing this, a large circle forms around the shoulder joint. The area surrounded by this circle is called the ‘mid-range’ of movement. In this area, the role of the negative intra-articular pressure subsides,7 the active compression of the rotator cuff muscles (specifically, supraspinatus, subscapularis, and infraspinatus) and the middle portion of the deltoid (partially)8 push the humeral head against the centre of the glenoid. This mechanism is defined as concavity-compression9 and is an important factor which further stabilizes the shoulder at the mid-range of movement.

As the shoulder joint approaches the end-range, the glenohumeral capsule and ligaments (superior, middle and inferior) act as the main stabilizers of the shoulder joint.1013 With the arm in abduction and external rotation, the anterior portion of the capsule and the inferior glenohumeral ligament (IGHL), namely its anterior band, become taut and play a major role in preventing the humeral head from dislocating anteriorly.14 The middle glenohumeral ligament (MGHL) serves a similar function by reaching its highest tension at 30–45 degrees of abduction and external rotation,15 while the superior glenohumeral ligament (SGHL) becomes tight in adduction and external rotation, thus functioning as an inferior stabilizer.16 Finally, the posterior band of the IGHL prevents posterior dislocation with the arm in flexion and internal rotation.14

Glenohumeral stability: the ‘bony factors’

When focusing solely on the bone, it is useful to look at the two individual ends of the shoulder joint (the glenoid cavity and the humeral head) and the relative structural variables which can influence stability, and then analyse how these factors interact under normal and pathological circumstances. This way, a systematic approach can be used when evaluating the unstable shoulder in clinical practice, by understanding the role of bone abnormalities (either acquired or congenital) and treating them accordingly, if deemed necessary.

The first factor that needs to be taken into account is the shape of the glenoid and its morphology. As previously mentioned, the socket is inherently small in size when compared to the humeral head; therefore, several factors come into play in order to maintain stability. Concavity-compression is the predominant mechanism by which the humeral head is centred in the glenoid cavity at the mid-range.17 As the head is pushed against the glenoid bone, its depth, width and version become relevant. The glenoid socket is twice as deep in the superior-inferior direction as in the anteroposterior (AP) direction;18 therefore, different amounts of displacing forces are needed to dislocate the humeral head in different directions. Lippitt et al19 quantified the amount of force needed to overcome the compressive force in different directions as suggested by Fukuda,20 introducing the concept of stability ratio as the translation force divided by the compressive force in different directions. They found that the stability ratio for the superior and inferior directions was about twice as great when compared to the anterior and posterior directions (64% versus 33–35%, respectively). They also concluded that this was related to the greater effective depth of the glenoid in these planes (4.8 mm versus 2.2 mm, respectively). In fact, a linear relationship exists between the effective depth of the glenoid concavity and the stability ratio. The clinical implications of a pathological loss of bone concavity were further studied by Moroder et al21,22 and Peltz et al,23 whose studies established a correlation between the loss of glenoid concavity and instability: in fact, both in traumatic and atraumatic shoulder instability, the glenoid displayed a flatter morphology and a higher radius of curvature (ROC) when compared to healthy volunteers with no history of shoulder pathology. In addition, ROC in the AP direction generally appeared greater than ROC in the supero-inferior direction, confirming previously published data on glenoid morphology,24 which could explain why a higher degree of instability is present in the AP direction compared to all others.

Glenoid version, defined as the orientation of the articular surface relative to the axis of the scapular body, is another variable which can influence stability, particularly in the posterior direction. It is best measured using advanced imaging techniques (i.e. computed tomography: CT)2528 and normally displays few degrees of retroversion with respect to the plane of the scapula (usually 1–7°, although quite some variation is reported in the literature in terms of range and average value).29,30 When the glenoid version is altered (i.e. due to dysplasia), it can affect stability in the AP plane.3135 This proves especially true when glenoid version approaches +10° of anteversion and −15° of retroversion,36 resulting in increased anterior and posterior instability, respectively. Edelson37 and Weishaupt et al38 have provided qualitative descriptions of glenoid dysplasia based on the morphology of the congenital bone deficit, by describing a spectrum of three different anatomic forms of the posterior glenoid rim at the base of the glenoid: pointed form (without bony deficiency), rounded glenoid deficiency (‘lazy J’ form), and triangular bony deficiency (‘delta’ form). In their analysis they also measured glenoid retroversion, which appeared to be significantly increased in posterior shoulder instability when compared to patients with anterior instability, later confirmed by the findings of Inui et al.39

Decreased retroversion and inferior inclination also seem to play a role in anterior shoulder stability. Hohmann and Tetsworth40 found a difference in glenoid version and inclination in patients who had sustained a prior anterior shoulder dislocation compared with the patients in the matched control group who underwent shoulder MRI for other causes: when compared to a healthy control group, the anterior dislocation group displayed −1.7°±4.5 (range: 0.9° to 2.5°) of retroversion and 1.6°±5.9 (range: 0.6° to 2.6°) of inferior inclination, as compared to values of −5.8°±4.6 (range: 5.0° to 6.8°) and 4.0°±6.8 (range: 2.8° to 5.2°) of retroversion and superior inclination, respectively.

Scapular positioning can also affect stability. Warner et al41 found that almost two thirds of instability patients showed alteration in scapulothoracic motion, probably due to muscle inhibition and poor dynamic control of the scapula itself.42 A systematic review by Struyf et al43 confirmed the alterations in scapulothoracic muscle activity in instability patients when compared to healthy controls, although no clear changes in activation patterns were identified. A cadaveric study by Kikuchi et al44 showed how posterior and inferior stability increased with an anterior tilt of more than 5° and with a superior tilt of 10°, respectively, whereas on the other hand the anterior and posterior stability decreased with an anterior tilt of 5° and with a posterior tilt of 15°, respectively.

Anatomical factors seem to play a far less important role, if any, on the humeral side. Several authors, while confirming the role of anatomical variations in the glenoid of unstable shoulders, have shown how these variations had no role on the humeral side. Early roentgenographic evaluations by Cyprien et al45 suggested no influence of humeral head torsion variation in normal and unstable shoulder. Further CT studies33,46 found no significant differences in glenohumeral index, humeral retrotorsion or variation in radius or width of the humeral head between patients with recurrent anterior shoulder instability and control patients.

Bone loss size and location: clinical relevance and management strategies

In most cases, forceful abduction and external rotation force the humeral head out of the glenoid in an anterior-inferior direction, although other mechanisms of injury have been recently suggested.47,48 After a traumatic episode, there is a high probability of bony lesions on both the humeral head and the glenoid socket. A posterolateral humeral head compression fracture, known as Hill–Sachs lesion (HSL), is therefore caused by the impact with the glenoid and is present in 65% to 67% of dislocations after the first episode and in 84% to 93% in recurrent dislocations.49,50 Posterior dislocation occurs much less frequently and is usually a result of direct trauma or seizure.51 In this case, an anterior-superior impaction fracture (‘reverse Hill–Sachs lesion’ or RHSL, first described by McLaughlin) is created by the postero-inferior glenoid rim and can be present in about 86% of first-time posterior dislocations.52

The glenoid socket bone can also be affected depending on the direction of the dislocation. In first-time unilateral anterior dislocation, glenoid bone loss (GBL) can occur in about 41% of cases. This percentage may rise to 86% in patients with recurrent unilateral anterior dislocation.53 This confirms the findings of Sugaya et al,54 who found bony lesions in the anterior-inferior portion of the glenoid in about 90% of cases, and further classified them into fragment-type and erosion/compression-type, a probable consequence of a strong or weak capsular tissue, respectively.55 Similar percentages of posterior-inferior GBL are found in the rarer occurrence of posterior instability.38,52

In the setting of shoulder instability, regardless of the direction, precise bone loss evaluation through three-dimensional CT scans is key.55,56,57 This happens when the glenoid and humeral bone loss interact in such a way that favours further dislocation, hence the HSL ‘engages’ the anterior glenoid defect and dislocates the humeral head from the socket.58 Therefore, HSL and glenoid bone deficits must be considered together. In the setting of anterior instability, it is important to determine how these affect the zone of contact between the glenoid and the humeral head, defined as ‘glenoid track’ (GT)59 (Fig. 1), which has been measured to correspond to about 83% of glenoid width in live shoulders60 and represents a key factor in maintaining joint stability. Quantitative and qualitative bone loss analysis is therefore crucial in determining the pathogenesis of recurrent instability and choosing an effective treatment strategy (i.e. ‘bone-block’ surgery versus capsulo-labral repair). Di Giacomo et al61 developed the concept of ‘on-track’ and ‘off-track’ shoulder lesions: when the HSL engages the anterior glenoid rim, it is defined as ‘off-track’; if it does not, it is an ‘on-track’ lesion. The surgeon must then understand which factors in glenoid and humeral bone loss can cause further instability, whether anterior or posterior. In other words, what features of the HSL and glenoid lesion drive the shoulder ‘off-track’ (Fig. 2). It is important to point out that this classification differs from the ‘engaging’-vs-‘non-engaging’ type in its very nature: the ‘on-track’-vs-‘off-track’ concept is evaluated through CT scan with the arm at rest, thus maintaining a fixed instantaneous center of rotation (ICR) of the humeral head. This is different from the ‘engaging’-vs-‘non-engaging’ classification, which is a clinical evaluation performed preoperatively under general anesthesia, where the humeral head dislocates due to the unrepaired Bankart lesion. In this case, the ICR migrates anteriorly. This leads to a reduction of the GT, therefore impairing evaluation. In our distinction, the ICR remains fixed and the GT is unaffected, thus leading to a more precise evaluation of the type of lesion and of the GT itself.

Fig. 1
Fig. 1

During arm motion towards the end-range, the glenoid moves along the contact zone on the posterior margin of the humeral articular surface, shifting from inferomedial to posterolateral. Reproduced with permission from Itoi E. 'On-track' and 'off-track' shoulder lesions. EFORT Open Rev 2017;2:343-351.

Citation: EFORT Open Reviews 3, 12; 10.1302/2058-5241.3.180028

Fig. 2
Fig. 2

The “on-track”/”off-track” concept in anterior shoulder instability from Di Giacomo et al.61 If HSL falls within the medial margin of the GT, there is still glenoid track support for bone stability (“on-track” HSL) and the HSL will not engage (above). If the HSL extends medial to the medial margin of the GT and there is concomitant loss of bone support at the anterior glenoid rim, the HSL will engage (“off-track HSL”)(below). Reproduced with permission from Elsevier.

Citation: EFORT Open Reviews 3, 12; 10.1302/2058-5241.3.180028

In terms of anterior-inferior GBL, several CT-based methods are available in order to achieve precise measurements,6267 usually expressed as a percentage of the total glenoid surface. Cadaveric studies by Yamamoto et al68 and Itoi et al69 proved how a GBL of 20–25% (equivalent to about 6 mm) can compromise the result of an isolated soft-tissue repair (i.e. Bankart repair with or without capsuloplasty), although this value might be as low as 13.5%, particularly in high-demand patients.70 To corroborate this, a subsequent cadaveric study by Arciero et al71 showed that, when an HSL is present, this deficit can be as small as 2 mm in order to compromise glenohumeral stability. This is further proof of the interdependence of the two lesions and reinforces the concept of the bipolar nature of anterior shoulder instability, which constitutes the majority of cases.53 In terms of HSL morphological features, its size, depth, width and orientation have all been thought to be parameters which could estimate the risk of engagement.72-76 However, their evaluation alone is not sufficient to evaluate the risk of recurrent instability. In fact, it is also critical to evaluate the position of the HSL. This is because with an increase in arm elevation, the contact area between the glenoid and the humeral head moves from the inferomedial to the superolateral portion of posterior articular surface of the humeral head; therefore, the larger the medial portion of the HSL that falls outside the GT, the higher the probability of recurrence,59 thus becoming an ‘off-track’ lesion with potential for re-engagement, even after capsulo-labral repair surgery. Categorizing HSLs as such can thus help the surgeon predict the chance of failure of arthroscopic stabilization (versus bone-block surgery) better than solely quantifying glenoid osseous defect.77 In addition, the presence of a GBL increases the likelihood of recurrence. This happens because the width of the glenoid is the only factor which influences the width of the GT.78 Therefore, an anterior rim deficit directly affects the width of the GT: the smaller the glenoid track, the higher the probability that the medial margin of the HSL falls outside its boundaries, creating an ‘insufficient’ GT. The new GT will therefore be equal to 83% of the diameter of the inferior glenoid minus the width of the anterior GBL. It can then be calculated using CT scans and superimposed onto the HSL in order to classify it as either ‘on-track’ or ‘off-track’ and treat it accordingly.

We can therefore summarize treatment options based on the percentage of GBL and type of HSL (Table 1). In general, we can adopt a cut-off value of 25% of GBL, beyond which bone-block surgery is mandatory, regardless of the type of HSL. Below 25% GBL, it could be said that a ‘grey area’ of treatment exists. Nevertheless, a further cut-off value of 13.5% GBL should be adopted:70 between 0% and 13.5%, an arthroscopic Bankart repair can be safely chosen as a treatment option when the lesion is ‘on-track’; between 13.5% and 25%, the same procedure can be effective in eliminating instability, but could result in reduced ROM, particularly in abduction and external rotation, as the repair is performed onto the bone loss, thus restricting capsular space and motion.69 In these cases, open inferior capsular shift and bone-block surgery are viable options. ‘Off-track’ lesions, on the other hand, have a higher risk of engagement, therefore an arthroscopic Bankart repair with an additional infraspinatus tenodesis onto the HSL (or ‘remplissage’) can transform the HSL from intra- to extra-articular, effectively addressing instability and lowering the recurrence rate.79 Because loss of external rotation is a well-known side effect of this procedure,80-81 open capsular shift and the Bristow–Latarjet procedure both represent a valid alternative should there be need for its complete restoration (e.g. in professional throwing athletes).

Table 1.

Antero-inferior shoulder instability treatment algorithm based on different combinations of GBL and type of HSL

‘On-track’ HSL‘Off-track’ HSL
0–13.5% GBLArthroscopic Bankart repair• Arthroscopic Bankart repair + remplissage

• Open inferior capsular shift

• Bone-block surgery (i.e. Bristow–Latarjet)
13.5–25% GBL (‘grey area’)• Arthroscopic Bankart repair

• Open inferior capsular shift

• Bone-block surgery (i.e. Bristow–Latarjet)
• Arthroscopic Bankart repair + remplissage

• Open inferior capsular shift

• Bone-block surgery (i.e. Bristow–Latarjet)
> 25% GBLBone-block surgery (i.e. Bristow–Latarjet)Bone-block surgery (i.e. Bristow–Latarjet)

Note. GBL, glenoid bone loss; HSL, Hill–Sachs lesion.

Similar conclusions have been drawn from studies about posterior instability. Nacca et al57 recently found the critical posterior GBL to be greater than or equal to 20% of the posterior glenoid width, leading to failure of isolated posterior Bankart repair. This result paves the ground for the decision-making process in posterior bone loss, as previous meta-analyses failed to identify high-quality studies which could indicate an adequate treatment algorithm for such lesions.82 This is due to the rarer (and therefore easily missed) occurrence of posterior instability in the setting of posterior shoulder dislocation, which is classically associated with epileptic seizure, electrocution accidents and high-energy trauma.83-84 Posterior GBL and RHSL are found in 9% and 39% of cases respectively, yet a combination of the two lesions seems to occur in only 2% of cases.82 Therefore, a high index of suspicion after an acute episode of posterior dislocation is a key step in identifying posterior instability. Once the diagnosis is made, evaluation of bone loss with the aid of CT scans will help assess the feature of bone deficits, similarly to the procedure applied in anterior instability. The proposed treatments available in the literature at this time are mostly solely based on the percentage of humeral head bone loss: if this is lower than 25%, it is most frequently managed with a posterior capsular repair, a closed reduction, or, rarely, an arthroscopic repair. A humeral head bone loss from 25% to 50% is mainly managed with an open reconstruction with bone graft or a subscapularis tendon transfer (McLaughlin technique). Finally, if the humeral head bone loss is > 50%, arthroplasty is the suggested choice.82

Moroder et al85 proposed a different approach to posterior instability by performing a CT best-fit circle measurement of the angle between the posterior RHSL edge and the bicipital sulcus (‘gamma angle’) and the angle between the posterior defect margin and the posterior glenoid rim (‘delta angle’)86 (Fig. 3). According to this data, a posterior glenoid bone defect can turn a non-engaging RSHL lesion into an engaging one when 2.3° per mm bone loss at the posterior glenoid rim plus the gamma angle is greater than 90°. They defined this as the ‘gamma angle concept’ (Fig. 4), confirming how posterior instability acts similarly to its anterior counterpart in terms of humeral head defect size and location in the risk of engagement, as the more medial and bigger the RHSL, the greater the gamma angle.86-87 In general, a gamma angle greater than 90° warrants surgical stabilization as it leads to a higher risk of recurrence (Fig. 5).

Fig. 3
Fig. 3

Illustrations of the measurements performed to determine the defect size and localization in posterior shoulder instability as proposed by Moroder et al.86 (A) Best-fit circle placed on the remainder of the humeral articular surface to create a reference centre for the measured angles; (B) alpha, defined as the angle between the anterior and posterior defect margin; (C) beta, defined as the angle between the anterior defect margin and the bicipital groove; (D) gamma, defined as the angle between the bicipital groove and the posterior defect margin; (E) delta, defined as the angle between the posterior defect margin and the posterior glenoid rim; and (F) epsilon, defined as the angle between the posterior defect margin and the anterior glenoid rim. Reproduced with permission from SAGE Publications.

Citation: EFORT Open Reviews 3, 12; 10.1302/2058-5241.3.180028

Fig. 4
Fig. 4

The gamma angle concept, as proposed by Moroder et al.85 Reproduced with permission from SAGE Publications.

Citation: EFORT Open Reviews 3, 12; 10.1302/2058-5241.3.180028

Fig. 5
Fig. 5

Schematic representation of the gamma angle concept applied to posterior instability. (A) Gamma angle <90°, (B) internal rotation does not engage the posterior glenoid. (C) Gamma angle >90°, (D) internal rotation engages the posterior glenoid. (E) When posterior GBL is present, about 2.3 degrees per mm of bone loss are lost on the delta angle. (F) In this case, concomitant posterior glenoid defects might lead to the engagement of noncritical RHSLs.

Note. BG: Bicipital Groove.

Citation: EFORT Open Reviews 3, 12; 10.1302/2058-5241.3.180028

Therefore, when evaluating bone loss in posterior shoulder instability, a cut-off value of 20% of posterior GBL generally warrants posterior bone-block stabilization surgery, achievable mainly through the use of posterior iliac bone graft88 as described by Levigne et al,89-90 while posterior GBL < 20% can be treated with good results with arthroscopic posterior capsulo-labral repair.91 In addition, the gamma angle concept proposed by Moroder et al can further help to identify those lesions which are prone to engagement and assist the surgeon in the decision-making process, especially in cases of bipolar bone lesion (RHSL with posterior GBL). Nevertheless, further clinical research is needed in order to determine whether the engagement predictions correlate with clinical instability.85 Until these kind of studies are available, it is reasonable to treat these lesions based on history and clinical evaluation, along with the aid of sagittal and axial CT scans to help evaluate the risk of chronic posterior instability by evaluating humeral and posterior glenoid bone loss and applying the gamma angle concept as previously described.

Conclusions

Abnormality of the dynamic interplay of bony structures in the setting of shoulder instability, either congenital or acquired, can both favour instability and impair surgical results if not diagnosed correctly. This is especially true in the evaluation of bone loss after an episode of traumatic shoulder dislocation, either in an anterior or posterior direction. Precise assessment of such lesions can be achieved through CT imaging, and an adequate evaluation methodology can guide surgeons in choosing the optimal type of stabilization surgery.

Open access

This article is distributed under the terms of the Creative Commons Attribution-Non Commercial 4.0 International (CC BY-NC 4.0) licence (https://creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed.

ICMJE Conflict of interest statement

G. Di Giacomo declares consultancy for Arthrex; royalties from Springer/Arthrex, activities outside the submitted work.

Funding statement

No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

References

  • 1.

    Kelkar R, Wang VM, Flatow EL et al.. Glenohumeral mechanics: a study of articular geometry, contact, and kinematics. J Shoulder Elbow Surg 2001;10:7384.

    • Search Google Scholar
    • Export Citation
  • 2.

    Habermeyer P, Schuller U, Wiedemann E. The intra-articular pressure of the shoulder: an experimental study on the role of the glenoid labrum in stabilizing the joint. Arthroscopy 1992;8:166172.

    • Search Google Scholar
    • Export Citation
  • 3.

    Kumar VP, Balasubramaniam P. The role of atmospheric pressure in stabilising the shoulder: an experimental study. J Bone Joint Surg Br 1985;67-B:719721.

    • Search Google Scholar
    • Export Citation
  • 4.

    Alexander S, Southgate DF, Bull AM, Wallace AL. The role of negative intraarticular pressure and the long head of biceps tendon on passive stability of the glenohumeral joint. J Shoulder Elbow Surg 2013;22:94101.

    • Search Google Scholar
    • Export Citation
  • 5.

    Harryman DT II, Sidles JA, Harris SL et al.. The role of the rotator interval capsule in passivemotion and stability of the shoulder. J Bone Joint Surg Am 1992;74:5366.

    • Search Google Scholar
    • Export Citation
  • 6.

    Itoi E, Morrey BF, An KN. Biomechanics of the shoulder. In: Matsen FA, Wirth MA, Lippitt SB, Rockwood CA, eds. The shoulder. Fourth ed. Philadelphia, PA: Saunders/Elsevier, 2009:213265.

    • Search Google Scholar
    • Export Citation
  • 7.

    Shibata Y, Takeshita M, Takagishi N. Intra-articular pressure of glenohumeral joint during movement. Katakansetsu 1986;10:3640.

  • 8.

    Yanagawa T, Goodwin CJ, Shelburne KB, Giphart JE, Torry MR, Pandy MG. Contributions of the individual muscles of the shoulder to glenohumeral joint stability during abduction. J Biomech Eng 2008;130:021024.

    • Search Google Scholar
    • Export Citation
  • 9.

    Lippitt SB, Vanderhoof JE, Harris SL et al.. Glenohumeral stability from concavity-compression: a quantitative analysis. J Shoulder Elbow Surg 1993;244:2735.

    • Search Google Scholar
    • Export Citation
  • 10.

    Blasier RB, Guldberg RE, Rothman ED. Anterior shoulder stability: contributions of rotator cuff forces and the capsular ligaments in a cadaver model. J Shoulder Elbow Surg 1992;1:140150.

    • Search Google Scholar
    • Export Citation
  • 11.

    Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill–Sachs lesion. Arthroscopy 2000;16:677694.

    • Search Google Scholar
    • Export Citation
  • 12.

    O’Connell PW, Nuber GW, Mileski RA, Lautenschlager E. The contribution of the glenohumeral ligaments to anterior stability of the shoulder joint. Am J Sports Med 1990;18(6):579-84.

    • Search Google Scholar
    • Export Citation
  • 13.

    Turkel SJ, Panio MW, Marshall JL, Girgis FG. Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint. J Bone Joint Surg Am 1981;63:12081217.

    • Search Google Scholar
    • Export Citation
  • 14.

    Urayama M, Itoi E, Hatakeyama Y et al.. Function of the 3 portions of the inferior glenohumeral ligament: a cadaveric study. J Shoulder Elbow Surg 2001;10:589594.

    • Search Google Scholar
    • Export Citation
  • 15.

    Gagey OJ, Boisrenoult P. Shoulder capsule shrinkage and consequences on shoulder movements. Clin Orthop Relat Res 2004;419:218222.

  • 16.

    Warner JJ, Deng XH, Warren RF et al.. Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint. Am J Sports Med 1992;20:675685.

    • Search Google Scholar
    • Export Citation
  • 17.

    Matsen FA III, Chebli C, Lippitt SB. Principles for the evaluation and management of shoulder instability. J Bone Joint Surg Am 2006;88:648659.

    • Search Google Scholar
    • Export Citation
  • 18.

    Howell SM, Galinat BJ. The glenoid-labral socket. A constrained articular surface.Clin Orthop Relat Res 1989;243:122-125

  • 19.

    Lippitt SB, Vanderhoof JE, Harris SL, Sidles JA, Harryman DT II, Matsen FA III. Glenohumeral stability from concavity-compression: a quantitative analysis. J Shoulder Elbow Surg 1993;2:2735.

    • Search Google Scholar
    • Export Citation
  • 20.

    Fukuda K, Chang Ming C, Cofield RH, Chao EY. Biomechanical analysis of stability and fixation strength of total shoulder prosthesis. Orthopedics 1988;11:141149.

    • Search Google Scholar
    • Export Citation
  • 21.

    Moroder P, Ernstbrunner L, Pomwenger W et al.. Anterior shoulder instability is associated with an underlying deficiency of the bony glenoid concavity. Arthroscopy 2015;31:12231231.

    • Search Google Scholar
    • Export Citation
  • 22.

    Moroder P, Haniel F, Quirchmayr M et al.. Effect of glenoid concavity loss on shoulder stability: a case report in a professional wrestler. BMC Musculoskelet Disord 2016;17:357.

    • Search Google Scholar
    • Export Citation
  • 23.

    Peltz CD, Zauel R, Ramo N, Mehran N, Moutzouros V, Bey MJ. Differences in glenohumeral joint 279 morphology between patients with anterior shoulder instability and healthy, uninjured 280 volunteers. J Shoulder Elbow Surg 2015;24:10141020.

    • Search Google Scholar
    • Export Citation
  • 24.

    McPherson EJ, Friedman RJ, An YH, Chokesi R, Dooley RL. Anthropometric study of normal glenohumeral relationships. J Shoulder Elbow Surg 1997;6:105112.

    • Search Google Scholar
    • Export Citation
  • 25.

    Friedman RJ, Hawthorne KB, Genez BM. The use of computerized tomography in the measurement of glenoid version. J Bone Joint Surg Am 1992;74:1032-7.

    • Search Google Scholar
    • Export Citation
  • 26.

    Nyffeler RW, Jost B, Pfirrmann CW, Gerber C. Measurement of glenoid version: conventional radiographs versus computed tomography scans. J Shoulder Elbow Surg 2003;12:493496.

    • Search Google Scholar
    • Export Citation
  • 27.

    Tétreault P, Krueger A, Zurakowski D, Gerber C. Glenoid version and rotator cuff tears. J Orthop Res 2004;22:202207.

  • 28.

    Maurer A, Fucentese SF, Pfirrmann CW et al.. Assessment of glenoid inclination on routine clinical radiographs and computed tomography examinations of the shoulder. J Shoulder Elbow Surg 2012;21:10961103.

    • Search Google Scholar
    • Export Citation
  • 29.

    Churchill RS, Brems JJ, Kotschi H. Glenoid size, inclination, and version: an anatomic study. J Shoulder Elbow Surg 2001;10:327-32.

  • 30.

    Eichinger JK, Galvin JW, Grassbaugh JA, Parada SA, Li X. Glenoid dysplasia: pathophysiology, diagnosis, and management. J Bone Joint Surg Am 2016;98:958968.

    • Search Google Scholar
    • Export Citation
  • 31.

    Brewer BJ, Wubben RC, Carrera GF. Excessive retroversion of the glenoid cavity: a cause of non-traumatic posterior instability of the shoulder. J Bone Joint Surg Am 1986;68:724731.

    • Search Google Scholar
    • Export Citation
  • 32.

    Grasshoff H, Buhtz C, Gellerich I et al.. CT diagnosis in instability of the shoulder joint. RoFo Fortschr Geb Rontgenstr Nuklearmed 1991;155:523526.

    • Search Google Scholar
    • Export Citation
  • 33.

    Hirschfelder H, Kirsten U. Biometric analysis of the unstable shoulder. Z Orthop Ihre Grenzgeb 1991;129:516520.

  • 34.

    Wirth MA, Seltzer DG, Rockwood CA Jr. Recurrent posterior glenohumeral dislocation associated with increased retroversion of the glenoid. Clin Orthop Relat Res 1994;308:98101.

    • Search Google Scholar
    • Export Citation
  • 35.

    Bradley JP, Forsythe B, Mascarenhas R. Arthroscopic management of posterior shoulder 308 instability: diagnosis, indications, and technique. Clin Sports Med 2008;27:649670.

    • Search Google Scholar
    • Export Citation
  • 36.

    Eichinger JK, Massimini DF, Kim J, Higgins LD. Biomechanical evaluation of glenoid version and dislocation direction on the influence of anterior shoulder instability and development of Hill–Sachs lesions. Am J Sports Med 2016;44:27922799.

    • Search Google Scholar
    • Export Citation
  • 37.

    Edelson JG. Localized glenoid hypoplasia: an anatomic variation of possible clinical significance. Clin Orthop Relat Res 1995;321:189195.

    • Search Google Scholar
    • Export Citation
  • 38.

    Weishaupt D, Zanetti M, Nyffeler RW, Gerber C, Hodler J. Posterior glenoid rim deficiency in recurrent (atraumatic) posterior shoulder instability. Skeletal Radiol 2000;29:204210.

    • Search Google Scholar
    • Export Citation
  • 39.

    Inui H, Sugamoto K, Miyamoto T et al.. Glenoid shape in atraumatic posterior instability of the shoulder. Clin Orthop Relat Res 2002;403:8792.

  • 40.

    Hohmann E, Tetsworth K. Glenoid version and inclination are risk factors for anterior shoulder dislocation. J Shoulder Elbow Surg 2015;24:12681273.

    • Search Google Scholar
    • Export Citation
  • 41.

    Warner JJ, Micheli LJ, Arslanian LE, Kennedy J, Kennedy R. Scapulothoracic motion in normal shoulders and shoulders with glenohumeral instability and impingement syndrome: a study using Moiré topographic analysis. Clin Orthop Relat Res 1992;285:191199.

    • Search Google Scholar
    • Export Citation
  • 42.

    Kibler WB. The role of the scapula in athletic shoulder function. Am J Sports Med 1998;26:325337.

  • 43.

    Struyf F, Cagnie B, Cools A et al.. Scapulothoracic muscle activity and recruitment timing in patients with shoulder impingement symptoms and glenohumeral instability. J Electromyogr Kinesiol 2014;24:277284.

    • Search Google Scholar
    • Export Citation
  • 44.

    Kikuchi K, Itoi E, Yamamoto N et al.. Scapular inclination and glenohumeral joint stability: a cadaveric study. J Orthop Sci 2008;13:7277.

  • 45.

    Cyprien JM, Vasey HM, Burdet A, Bonvin JC, Kritsikis N, Vuagnat P. Humeral retrotorsion and glenohumeral relationship in the normal shoulder and in recurrent anterior dislocation (scapulometry). Clin Orthop Relat Res 1983;175:817.

    • Search Google Scholar
    • Export Citation
  • 46.

    Randelli M, Gambrioli PL. Glenohumeral osteometry by computed tomography in normal and unstable shoulders. Clin Orthop Relat Res 1986;208:151156.

    • Search Google Scholar
    • Export Citation
  • 47.

    Crichton J, Jones DR, Funk L. Mechanisms of traumatic shoulder injury in elite rugby players. Br J Sports Med 2012;46:538542.

  • 48.

    Longo UG, Huijsmans PE, Maffulli N, Denaro V, De Beer JF. Video analysis of the mechanisms of shoulder dislocation in four elite rugby players. J Orthop Sci 2011;16:389397.

    • Search Google Scholar
    • Export Citation
  • 49.

    Spatschil A, Landsiedl F, Anderl W et al.. Posttraumatic anterior-inferior instability of the shoulder: arthroscopic findings and clinical correlations. Arch Orthop Trauma Surg 2006;126:217222.

    • Search Google Scholar
    • Export Citation
  • 50.

    Yiannakopoulos CK, Mataragas E, Antonogiannakis E. A comparison of the spectrum of intra-articular lesions in acute and chronic anterior shoulder instability. Arthroscopy 2007;23:985990.

    • Search Google Scholar
    • Export Citation
  • 51.

    Robinson CM, Seah M, Akhtar MA. The epidemiology, risk of recurrence, and functional outcome after an acute traumatic posterior dislocation of the shoulder. J Bone Joint Surg Am 2011;93:16051613.

    • Search Google Scholar
    • Export Citation
  • 52.

    Saupe N, White LM, Bleakney R. Acute traumatic posterior shoulder dislocation: MR findings. Radiology 2008;248:185193.

  • 53.

    Griffith JF, Antonio GE, Yung PS et al.. Prevalence, pattern, and spectrum of glenoid bone loss in anterior shoulder dislocation: CT analysis of 218 patients. AJR Am J Roentgenol 2008;190:12471254.

    • Search Google Scholar
    • Export Citation
  • 54.

    Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg [Am] 2003;85:878884.

    • Search Google Scholar
    • Export Citation
  • 55.

    Boileau P, Villalba M, Héry JY, Balg F, Ahrens P, Neyton L. Risk factors for recurrence of shoulder instability after arthroscopic Bankart repair. J Bone Joint Surg Am 2006;88:17551756.

    • Search Google Scholar
    • Export Citation
  • 56.

    Saliken DJ, Bornes TD, Bouliane MJ, Sheps DM, Beaupre LA. Imaging methods for quantifying glenoid and Hill–Sachs bone loss in traumatic instability of the shoulder: a scoping review. BMC Musculoskelet Disord 2015;16:164.

    • Search Google Scholar
    • Export Citation
  • 57.

    Nacca C, Gil JA, Badida R, Crisco JJ, Owens BD. Critical glenoid bone loss in posterior shoulder instability. Am J Sports Med 2018; 46:10581063.

  • 58.

    Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill–Sachs lesion. Arthroscopy 2000;16:6.

    • Search Google Scholar
    • Export Citation
  • 59.

    Itoi E. 'On-track' and 'off-track' shoulder lesions. EFORT Open Rev 2017;2:343-351.

  • 60.

    Omori Y, Yamamoto N, Koishi H et al.. Measurement of the glenoid track in vivo, investigated by the three-dimensional motion analysis using open MRI. Poster 502. Presented at the 57th Annual Meeting of the Orthopaedic Research Society, Long Beach, CA, 13–16 January 2011.

    • Search Google Scholar
    • Export Citation
  • 61.

    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;30:9098.

    • Search Google Scholar
    • Export Citation
  • 62.

    Barchilon VS, Kotz E, Barchilon Ben-Av M, Glazer E, Nyska M. A simple method for quantitative evaluation of the missing area of the anterior glenoid in anterior instability of the glenohumeral joint. Skeletal Radiol 2008;37:731736.

    • Search Google Scholar
    • Export Citation
  • 63.

    Baudi P, Righi P, Bolognesi D et al.. How to identify and calculate glenoid bone deficit. Chir Organi Mov 2005;90:145152.

  • 64.

    Chuang TY, Adams CR, Burkhart SS. Use of preoperative three-dimensional computed tomography to quantify glenoid bone loss in shoulder instability. Arthroscopy 2008;24:376382.

    • Search Google Scholar
    • Export Citation
  • 65.

    Gerber C, Nyffeler RW. Classification of glenohumeral joint instability. Clin Orthop Relat Res 2002;400:6576.

  • 66.

    Sugaya H, Kon Y, Tsuchiya A. Arthroscopic repair of glenoid fractures using suture anchors. Arthroscopy 2005;21:635.

  • 67.

    Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg 2003;85:878–84.

    • Search Google Scholar
    • Export Citation
  • 68.

    Yamamoto N, Itoi E, Abe H et al.. Effect of an anterior glenoid defect on anterior shoulder stability. Am J Sports Med 2009;37:949954.

  • 69.

    Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: a cadaveric study. J Bone Joint Surg Am 2000;82:3546.

    • Search Google Scholar
    • Export Citation
  • 70.

    Shaha JS, Cook JB, Song DJ et al.. Redefining ‘critical’ bone loss in shoulder instability: functional outcomes worsen with ‘subcritical’ bone loss. Am J Sports Med 2015;43:17191725.

    • Search Google Scholar
    • Export Citation
  • 71.

    Arciero RA, Parrino A, Bernhardson AS et al.. The effect of a combined glenoid and Hill–Sachs defect on glenohumeral stability: a biomechanical cadaveric study using 3-dimensional modeling of 142 patients. Am J Sports Med 2015;43:14221429.

    • Search Google Scholar
    • Export Citation
  • 72.

    Cho SH, Cho NS, Rhee YG. Preoperative analysis of the Hill–Sachs lesion in anterior shoulder instability: how to predict engagement of the lesion. Am J Sports Med 2011;39:23892395.

    • Search Google Scholar
    • Export Citation
  • 73.

    Kaar SG, Fening SD, Jones MH, Colbrunn RW, Miniaci A. Effect of humeral head defect size on glenohumeral stability: a cadaveric study of simulated Hill–Sachs defects. Am J Sports Med 2010;38:594599.

    • Search Google Scholar
    • Export Citation
  • 74.

    Ozaki R, Nakagawa S, Mizuno N, Mae T, Yoneda M. Hill–Sachs lesions in shoulders with traumatic anterior instability: evaluation using computed tomography with 3-dimensional reconstruction. Am J Sports Med 2014;42:25972605.

    • Search Google Scholar
    • Export Citation
  • 75.

    Rowe CR, Zarins B, Ciullo JV. Recurrent anterior dislocation of the shoulder after surgical repair: apparent causes of failure and treatment. J Bone Joint Surg Am 1984;66:159168.

    • Search Google Scholar
    • Export Citation
  • 76.

    Sommaire C, Penz C, Clavert P, Klouche S, Hardy P, Kempf JF. Recurrence after arthroscopic Bankart repair: is quantitative radiological analysis of bone loss of any predictive value? Orthop Traumatol Surg Res 2012;98:514519.

    • Search Google Scholar
    • Export Citation
  • 77.

    Cook JB, Shaha JS, Rowles DJ, Bottoni CR, Shaha S, Tokish JM. Clinical validation of the ‘on-track’ vs. ‘off-track’ concept in anterior glenohumeral instability. Paper presented at the 2015 Annual Meeting, American Academy of Orthopaedic Surgeons, 24–28 March 2015, Las Vegas, NV.

    • Search Google Scholar
    • Export Citation
  • 78.

    Yamamoto N, Itoi E, Abe H et al.. Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: new concept of glenoid track. J Shoulder Elbow Surg 2007;16:649656.

    • Search Google Scholar
    • Export Citation
  • 79.

    Purchase RJ, Wolf EM, Hobgood ER, Pollock ME, Smalley CC. Hill–Sachs ‘remplissage’: an arthroscopic solution for the engaging Hill–Sachs lesion. Arthroscopy 2008;24:723726.

    • Search Google Scholar
    • Export Citation
  • 80.

    Boileau P, O’Shea K, Vargas P et al.. Anatomical and functional results after arthroscopic Hill–Sachs remplissage. J Bone Joint Surg Am 2012;94:618626.

    • Search Google Scholar
    • Export Citation
  • 81.

    Merolla G, Paladini P, Di Napoli G et al.. Outcomes of arthroscopic Hill–Sachs remplissage and anterior Bankart repair: a retrospective controlled study including ultrasound evaluation of posterior capsulotenodesis and infraspinatus strength assessment. Am J Sports Med 2015;43:407414.

    • Search Google Scholar
    • Export Citation
  • 82.

    Longo UG, Rizzello G, Locher J et al.. Bone loss in patients with posterior gleno-humeral instability: a systematic review. Knee Surg Sports Traumatol Arthrosc 2016;24:612617.

    • Search Google Scholar
    • Export Citation
  • 83.

    Kowalsky MS, Levine WN. Traumatic posterior glenohumeral dislocation: classification, pathoanatomy, diagnosis, and treatment. Orthop Clin North Am 2008;39:519533, viii.

    • Search Google Scholar
    • Export Citation
  • 84.

    Rouleau DM, Hebert-Davies J. Incidence of associated injury in posterior shoulder dislocation: systematic review of the literature. J Orthop Trauma 2012;26:246251.

    • Search Google Scholar
    • Export Citation
  • 85.

    Moroder P, Plachel F, Tauber M et al.. Risk of engagement of bipolar bone defects in posterior shoulder instability. Am J Sports Med 2017;45:28352839.

    • Search Google Scholar
    • Export Citation
  • 86.

    Moroder P, Runer A, Kraemer M et al.. Influence of defect size and localization on the engagement of reverse Hill–Sachs lesions. Am J Sports Med 2015;43:542548.

    • Search Google Scholar
    • Export Citation
  • 87.

    Moroder P, Tauber M, Scheibel M et al.. Defect characteristics of reverse Hill–Sachs lesions. Am J Sports Med 2016;44:708714.

  • 88.

    Servien E, Walch G, Cortes ZE, Edwards TB, O’Connor DP. Posterior bone block procedure for posterior shoulder instability. Knee Surg Sports Traumatol Arthrosc 2007;15:11301136.

    • Search Google Scholar
    • Export Citation
  • 89.

    Levigne C, Garret J, Walch G. Posterior bone block for posterior instability. Knee Surg Sports Traumatol Arthrosc 2007;15:11301136.

  • 90.

    Levigne C, Walch G. Osteotomy and bone block techniques for posterior glenohumeral instability. In: Fu FH, Ticker JB, Imhoff AB, eds. An atlas of shoulder surgery. London: Martin Dunitz, 1998:4756.

    • Search Google Scholar
    • Export Citation
  • 91.

    Williams RJ, Strickland S, Cohen M, Altchek DW, Warren RF. Arthroscopic repair for traumatic posterior shoulder instability. Am J Sports Med 2003;31:203209.

    • Search Google Scholar
    • Export Citation

 

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  • View in gallery

    During arm motion towards the end-range, the glenoid moves along the contact zone on the posterior margin of the humeral articular surface, shifting from inferomedial to posterolateral. Reproduced with permission from Itoi E. 'On-track' and 'off-track' shoulder lesions. EFORT Open Rev 2017;2:343-351.

  • View in gallery

    The “on-track”/”off-track” concept in anterior shoulder instability from Di Giacomo et al.61 If HSL falls within the medial margin of the GT, there is still glenoid track support for bone stability (“on-track” HSL) and the HSL will not engage (above). If the HSL extends medial to the medial margin of the GT and there is concomitant loss of bone support at the anterior glenoid rim, the HSL will engage (“off-track HSL”)(below). Reproduced with permission from Elsevier.

  • View in gallery

    Illustrations of the measurements performed to determine the defect size and localization in posterior shoulder instability as proposed by Moroder et al.86 (A) Best-fit circle placed on the remainder of the humeral articular surface to create a reference centre for the measured angles; (B) alpha, defined as the angle between the anterior and posterior defect margin; (C) beta, defined as the angle between the anterior defect margin and the bicipital groove; (D) gamma, defined as the angle between the bicipital groove and the posterior defect margin; (E) delta, defined as the angle between the posterior defect margin and the posterior glenoid rim; and (F) epsilon, defined as the angle between the posterior defect margin and the anterior glenoid rim. Reproduced with permission from SAGE Publications.

  • View in gallery

    The gamma angle concept, as proposed by Moroder et al.85 Reproduced with permission from SAGE Publications.

  • View in gallery

    Schematic representation of the gamma angle concept applied to posterior instability. (A) Gamma angle <90°, (B) internal rotation does not engage the posterior glenoid. (C) Gamma angle >90°, (D) internal rotation engages the posterior glenoid. (E) When posterior GBL is present, about 2.3 degrees per mm of bone loss are lost on the delta angle. (F) In this case, concomitant posterior glenoid defects might lead to the engagement of noncritical RHSLs.

    Note. BG: Bicipital Groove.

  • 1.

    Kelkar R, Wang VM, Flatow EL et al.. Glenohumeral mechanics: a study of articular geometry, contact, and kinematics. J Shoulder Elbow Surg 2001;10:7384.

    • Search Google Scholar
    • Export Citation
  • 2.

    Habermeyer P, Schuller U, Wiedemann E. The intra-articular pressure of the shoulder: an experimental study on the role of the glenoid labrum in stabilizing the joint. Arthroscopy 1992;8:166172.

    • Search Google Scholar
    • Export Citation
  • 3.

    Kumar VP, Balasubramaniam P. The role of atmospheric pressure in stabilising the shoulder: an experimental study. J Bone Joint Surg Br 1985;67-B:719721.

    • Search Google Scholar
    • Export Citation
  • 4.

    Alexander S, Southgate DF, Bull AM, Wallace AL. The role of negative intraarticular pressure and the long head of biceps tendon on passive stability of the glenohumeral joint. J Shoulder Elbow Surg 2013;22:94101.

    • Search Google Scholar
    • Export Citation
  • 5.

    Harryman DT II, Sidles JA, Harris SL et al.. The role of the rotator interval capsule in passivemotion and stability of the shoulder. J Bone Joint Surg Am 1992;74:5366.

    • Search Google Scholar
    • Export Citation
  • 6.

    Itoi E, Morrey BF, An KN. Biomechanics of the shoulder. In: Matsen FA, Wirth MA, Lippitt SB, Rockwood CA, eds. The shoulder. Fourth ed. Philadelphia, PA: Saunders/Elsevier, 2009:213265.

    • Search Google Scholar
    • Export Citation
  • 7.

    Shibata Y, Takeshita M, Takagishi N. Intra-articular pressure of glenohumeral joint during movement. Katakansetsu 1986;10:3640.

  • 8.

    Yanagawa T, Goodwin CJ, Shelburne KB, Giphart JE, Torry MR, Pandy MG. Contributions of the individual muscles of the shoulder to glenohumeral joint stability during abduction. J Biomech Eng 2008;130:021024.

    • Search Google Scholar
    • Export Citation
  • 9.

    Lippitt SB, Vanderhoof JE, Harris SL et al.. Glenohumeral stability from concavity-compression: a quantitative analysis. J Shoulder Elbow Surg 1993;244:2735.

    • Search Google Scholar
    • Export Citation
  • 10.

    Blasier RB, Guldberg RE, Rothman ED. Anterior shoulder stability: contributions of rotator cuff forces and the capsular ligaments in a cadaver model. J Shoulder Elbow Surg 1992;1:140150.

    • Search Google Scholar
    • Export Citation
  • 11.

    Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill–Sachs lesion. Arthroscopy 2000;16:677694.

    • Search Google Scholar
    • Export Citation
  • 12.

    O’Connell PW, Nuber GW, Mileski RA, Lautenschlager E. The contribution of the glenohumeral ligaments to anterior stability of the shoulder joint. Am J Sports Med 1990;18(6):579-84.

    • Search Google Scholar
    • Export Citation
  • 13.

    Turkel SJ, Panio MW, Marshall JL, Girgis FG. Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint. J Bone Joint Surg Am 1981;63:12081217.

    • Search Google Scholar
    • Export Citation
  • 14.

    Urayama M, Itoi E, Hatakeyama Y et al.. Function of the 3 portions of the inferior glenohumeral ligament: a cadaveric study. J Shoulder Elbow Surg 2001;10:589594.

    • Search Google Scholar
    • Export Citation
  • 15.

    Gagey OJ, Boisrenoult P. Shoulder capsule shrinkage and consequences on shoulder movements. Clin Orthop Relat Res 2004;419:218222.

  • 16.

    Warner JJ, Deng XH, Warren RF et al.. Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint. Am J Sports Med 1992;20:675685.

    • Search Google Scholar
    • Export Citation
  • 17.

    Matsen FA III, Chebli C, Lippitt SB. Principles for the evaluation and management of shoulder instability. J Bone Joint Surg Am 2006;88:648659.

    • Search Google Scholar
    • Export Citation
  • 18.

    Howell SM, Galinat BJ. The glenoid-labral socket. A constrained articular surface.Clin Orthop Relat Res 1989;243:122-125

  • 19.

    Lippitt SB, Vanderhoof JE, Harris SL, Sidles JA, Harryman DT II, Matsen FA III. Glenohumeral stability from concavity-compression: a quantitative analysis. J Shoulder Elbow Surg 1993;2:2735.

    • Search Google Scholar
    • Export Citation
  • 20.

    Fukuda K, Chang Ming C, Cofield RH, Chao EY. Biomechanical analysis of stability and fixation strength of total shoulder prosthesis. Orthopedics 1988;11:141149.

    • Search Google Scholar
    • Export Citation
  • 21.

    Moroder P, Ernstbrunner L, Pomwenger W et al.. Anterior shoulder instability is associated with an underlying deficiency of the bony glenoid concavity. Arthroscopy 2015;31:12231231.

    • Search Google Scholar
    • Export Citation
  • 22.

    Moroder P, Haniel F, Quirchmayr M et al.. Effect of glenoid concavity loss on shoulder stability: a case report in a professional wrestler. BMC Musculoskelet Disord 2016;17:357.

    • Search Google Scholar
    • Export Citation
  • 23.

    Peltz CD, Zauel R, Ramo N, Mehran N, Moutzouros V, Bey MJ. Differences in glenohumeral joint 279 morphology between patients with anterior shoulder instability and healthy, uninjured 280 volunteers. J Shoulder Elbow Surg 2015;24:10141020.

    • Search Google Scholar
    • Export Citation
  • 24.

    McPherson EJ, Friedman RJ, An YH, Chokesi R, Dooley RL. Anthropometric study of normal glenohumeral relationships. J Shoulder Elbow Surg 1997;6:105112.

    • Search Google Scholar
    • Export Citation
  • 25.

    Friedman RJ, Hawthorne KB, Genez BM. The use of computerized tomography in the measurement of glenoid version. J Bone Joint Surg Am 1992;74:1032-7.

    • Search Google Scholar
    • Export Citation
  • 26.

    Nyffeler RW, Jost B, Pfirrmann CW, Gerber C. Measurement of glenoid version: conventional radiographs versus computed tomography scans. J Shoulder Elbow Surg 2003;12:493496.

    • Search Google Scholar
    • Export Citation
  • 27.

    Tétreault P, Krueger A, Zurakowski D, Gerber C. Glenoid version and rotator cuff tears. J Orthop Res 2004;22:202207.

  • 28.

    Maurer A, Fucentese SF, Pfirrmann CW et al.. Assessment of glenoid inclination on routine clinical radiographs and computed tomography examinations of the shoulder. J Shoulder Elbow Surg 2012;21:10961103.

    • Search Google Scholar
    • Export Citation
  • 29.

    Churchill RS, Brems JJ, Kotschi H. Glenoid size, inclination, and version: an anatomic study. J Shoulder Elbow Surg 2001;10:327-32.

  • 30.

    Eichinger JK, Galvin JW, Grassbaugh JA, Parada SA, Li X. Glenoid dysplasia: pathophysiology, diagnosis, and management. J Bone Joint Surg Am 2016;98:958968.

    • Search Google Scholar
    • Export Citation
  • 31.

    Brewer BJ, Wubben RC, Carrera GF. Excessive retroversion of the glenoid cavity: a cause of non-traumatic posterior instability of the shoulder. J Bone Joint Surg Am 1986;68:724731.

    • Search Google Scholar
    • Export Citation
  • 32.

    Grasshoff H, Buhtz C, Gellerich I et al.. CT diagnosis in instability of the shoulder joint. RoFo Fortschr Geb Rontgenstr Nuklearmed 1991;155:523526.

    • Search Google Scholar
    • Export Citation
  • 33.

    Hirschfelder H, Kirsten U. Biometric analysis of the unstable shoulder. Z Orthop Ihre Grenzgeb 1991;129:516520.

  • 34.

    Wirth MA, Seltzer DG, Rockwood CA Jr. Recurrent posterior glenohumeral dislocation associated with increased retroversion of the glenoid. Clin Orthop Relat Res 1994;308:98101.

    • Search Google Scholar
    • Export Citation
  • 35.

    Bradley JP, Forsythe B, Mascarenhas R. Arthroscopic management of posterior shoulder 308 instability: diagnosis, indications, and technique. Clin Sports Med 2008;27:649670.

    • Search Google Scholar
    • Export Citation
  • 36.

    Eichinger JK, Massimini DF, Kim J, Higgins LD. Biomechanical evaluation of glenoid version and dislocation direction on the influence of anterior shoulder instability and development of Hill–Sachs lesions. Am J Sports Med 2016;44:27922799.

    • Search Google Scholar
    • Export Citation
  • 37.

    Edelson JG. Localized glenoid hypoplasia: an anatomic variation of possible clinical significance. Clin Orthop Relat Res 1995;321:189195.

    • Search Google Scholar
    • Export Citation
  • 38.

    Weishaupt D, Zanetti M, Nyffeler RW, Gerber C, Hodler J. Posterior glenoid rim deficiency in recurrent (atraumatic) posterior shoulder instability. Skeletal Radiol 2000;29:204210.

    • Search Google Scholar
    • Export Citation
  • 39.

    Inui H, Sugamoto K, Miyamoto T et al.. Glenoid shape in atraumatic posterior instability of the shoulder. Clin Orthop Relat Res 2002;403:8792.

  • 40.

    Hohmann E, Tetsworth K. Glenoid version and inclination are risk factors for anterior shoulder dislocation. J Shoulder Elbow Surg 2015;24:12681273.

    • Search Google Scholar
    • Export Citation
  • 41.

    Warner JJ, Micheli LJ, Arslanian LE, Kennedy J, Kennedy R. Scapulothoracic motion in normal shoulders and shoulders with glenohumeral instability and impingement syndrome: a study using Moiré topographic analysis. Clin Orthop Relat Res 1992;285:191199.

    • Search Google Scholar
    • Export Citation
  • 42.

    Kibler WB. The role of the scapula in athletic shoulder function. Am J Sports Med 1998;26:325337.

  • 43.

    Struyf F, Cagnie B, Cools A et al.. Scapulothoracic muscle activity and recruitment timing in patients with shoulder impingement symptoms and glenohumeral instability. J Electromyogr Kinesiol 2014;24:277284.

    • Search Google Scholar
    • Export Citation
  • 44.

    Kikuchi K, Itoi E, Yamamoto N et al.. Scapular inclination and glenohumeral joint stability: a cadaveric study. J Orthop Sci 2008;13:7277.

  • 45.

    Cyprien JM, Vasey HM, Burdet A, Bonvin JC, Kritsikis N, Vuagnat P. Humeral retrotorsion and glenohumeral relationship in the normal shoulder and in recurrent anterior dislocation (scapulometry). Clin Orthop Relat Res 1983;175:817.

    • Search Google Scholar
    • Export Citation
  • 46.

    Randelli M, Gambrioli PL. Glenohumeral osteometry by computed tomography in normal and unstable shoulders. Clin Orthop Relat Res 1986;208:151156.

    • Search Google Scholar
    • Export Citation
  • 47.

    Crichton J, Jones DR, Funk L. Mechanisms of traumatic shoulder injury in elite rugby players. Br J Sports Med 2012;46:538542.

  • 48.

    Longo UG, Huijsmans PE, Maffulli N, Denaro V, De Beer JF. Video analysis of the mechanisms of shoulder dislocation in four elite rugby players. J Orthop Sci 2011;16:389397.

    • Search Google Scholar
    • Export Citation
  • 49.

    Spatschil A, Landsiedl F, Anderl W et al.. Posttraumatic anterior-inferior instability of the shoulder: arthroscopic findings and clinical correlations. Arch Orthop Trauma Surg 2006;126:217222.

    • Search Google Scholar
    • Export Citation
  • 50.

    Yiannakopoulos CK, Mataragas E, Antonogiannakis E. A comparison of the spectrum of intra-articular lesions in acute and chronic anterior shoulder instability. Arthroscopy 2007;23:985990.

    • Search Google Scholar
    • Export Citation
  • 51.

    Robinson CM, Seah M, Akhtar MA. The epidemiology, risk of recurrence, and functional outcome after an acute traumatic posterior dislocation of the shoulder. J Bone Joint Surg Am 2011;93:16051613.

    • Search Google Scholar
    • Export Citation
  • 52.

    Saupe N, White LM, Bleakney R. Acute traumatic posterior shoulder dislocation: MR findings. Radiology 2008;248:185193.

  • 53.

    Griffith JF, Antonio GE, Yung PS et al.. Prevalence, pattern, and spectrum of glenoid bone loss in anterior shoulder dislocation: CT analysis of 218 patients. AJR Am J Roentgenol 2008;190:12471254.

    • Search Google Scholar
    • Export Citation
  • 54.

    Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg [Am] 2003;85:878884.

    • Search Google Scholar
    • Export Citation
  • 55.

    Boileau P, Villalba M, Héry JY, Balg F, Ahrens P, Neyton L. Risk factors for recurrence of shoulder instability after arthroscopic Bankart repair. J Bone Joint Surg Am 2006;88:17551756.

    • Search Google Scholar
    • Export Citation
  • 56.

    Saliken DJ, Bornes TD, Bouliane MJ, Sheps DM, Beaupre LA. Imaging methods for quantifying glenoid and Hill–Sachs bone loss in traumatic instability of the shoulder: a scoping review. BMC Musculoskelet Disord 2015;16:164.

    • Search Google Scholar
    • Export Citation
  • 57.

    Nacca C, Gil JA, Badida R, Crisco JJ, Owens BD. Critical glenoid bone loss in posterior shoulder instability. Am J Sports Med 2018; 46:10581063.

  • 58.

    Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill–Sachs lesion. Arthroscopy 2000;16:6.

    • Search Google Scholar
    • Export Citation
  • 59.

    Itoi E. 'On-track' and 'off-track' shoulder lesions. EFORT Open Rev 2017;2:343-351.

  • 60.

    Omori Y, Yamamoto N, Koishi H et al.. Measurement of the glenoid track in vivo, investigated by the three-dimensional motion analysis using open MRI. Poster 502. Presented at the 57th Annual Meeting of the Orthopaedic Research Society, Long Beach, CA, 13–16 January 2011.

    • Search Google Scholar
    • Export Citation
  • 61.

    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;30:9098.

    • Search Google Scholar
    • Export Citation
  • 62.

    Barchilon VS, Kotz E, Barchilon Ben-Av M, Glazer E, Nyska M. A simple method for quantitative evaluation of the missing area of the anterior glenoid in anterior instability of the glenohumeral joint. Skeletal Radiol 2008;37:731736.

    • Search Google Scholar
    • Export Citation
  • 63.

    Baudi P, Righi P, Bolognesi D et al.. How to identify and calculate glenoid bone deficit. Chir Organi Mov 2005;90:145152.

  • 64.

    Chuang TY, Adams CR, Burkhart SS. Use of preoperative three-dimensional computed tomography to quantify glenoid bone loss in shoulder instability. Arthroscopy 2008;24:376382.

    • Search Google Scholar
    • Export Citation
  • 65.

    Gerber C, Nyffeler RW. Classification of glenohumeral joint instability. Clin Orthop Relat Res 2002;400:6576.

  • 66.

    Sugaya H, Kon Y, Tsuchiya A. Arthroscopic repair of glenoid fractures using suture anchors. Arthroscopy 2005;21:635.

  • 67.

    Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg 2003;85:878–84.

    • Search Google Scholar
    • Export Citation
  • 68.

    Yamamoto N, Itoi E, Abe H et al.. Effect of an anterior glenoid defect on anterior shoulder stability. Am J Sports Med 2009;37:949954.

  • 69.

    Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: a cadaveric study. J Bone Joint Surg Am 2000;82:3546.

    • Search Google Scholar
    • Export Citation
  • 70.

    Shaha JS, Cook JB, Song DJ et al.. Redefining ‘critical’ bone loss in shoulder instability: functional outcomes worsen with ‘subcritical’ bone loss. Am J Sports Med 2015;43:17191725.

    • Search Google Scholar
    • Export Citation
  • 71.

    Arciero RA, Parrino A, Bernhardson AS et al.. The effect of a combined glenoid and Hill–Sachs defect on glenohumeral stability: a biomechanical cadaveric study using 3-dimensional modeling of 142 patients. Am J Sports Med 2015;43:14221429.

    • Search Google Scholar
    • Export Citation
  • 72.

    Cho SH, Cho NS, Rhee YG. Preoperative analysis of the Hill–Sachs lesion in anterior shoulder instability: how to predict engagement of the lesion. Am J Sports Med 2011;39:23892395.

    • Search Google Scholar
    • Export Citation
  • 73.

    Kaar SG, Fening SD, Jones MH, Colbrunn RW, Miniaci A. Effect of humeral head defect size on glenohumeral stability: a cadaveric study of simulated Hill–Sachs defects. Am J Sports Med 2010;38:594599.

    • Search Google Scholar
    • Export Citation
  • 74.

    Ozaki R, Nakagawa S, Mizuno N, Mae T, Yoneda M. Hill–Sachs lesions in shoulders with traumatic anterior instability: evaluation using computed tomography with 3-dimensional reconstruction. Am J Sports Med 2014;42:25972605.

    • Search Google Scholar
    • Export Citation
  • 75.

    Rowe CR, Zarins B, Ciullo JV. Recurrent anterior dislocation of the shoulder after surgical repair: apparent causes of failure and treatment. J Bone Joint Surg Am 1984;66:159168.

    • Search Google Scholar
    • Export Citation
  • 76.

    Sommaire C, Penz C, Clavert P, Klouche S, Hardy P, Kempf JF. Recurrence after arthroscopic Bankart repair: is quantitative radiological analysis of bone loss of any predictive value? Orthop Traumatol Surg Res 2012;98:514519.

    • Search Google Scholar
    • Export Citation
  • 77.

    Cook JB, Shaha JS, Rowles DJ, Bottoni CR, Shaha S, Tokish JM. Clinical validation of the ‘on-track’ vs. ‘off-track’ concept in anterior glenohumeral instability. Paper presented at the 2015 Annual Meeting, American Academy of Orthopaedic Surgeons, 24–28 March 2015, Las Vegas, NV.

    • Search Google Scholar
    • Export Citation
  • 78.

    Yamamoto N, Itoi E, Abe H et al.. Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: new concept of glenoid track. J Shoulder Elbow Surg 2007;16:649656.

    • Search Google Scholar
    • Export Citation
  • 79.

    Purchase RJ, Wolf EM, Hobgood ER, Pollock ME, Smalley CC. Hill–Sachs ‘remplissage’: an arthroscopic solution for the engaging Hill–Sachs lesion. Arthroscopy 2008;24:723726.

    • Search Google Scholar
    • Export Citation
  • 80.

    Boileau P, O’Shea K, Vargas P et al.. Anatomical and functional results after arthroscopic Hill–Sachs remplissage. J Bone Joint Surg Am 2012;94:618626.

    • Search Google Scholar
    • Export Citation
  • 81.

    Merolla G, Paladini P, Di Napoli G et al.. Outcomes of arthroscopic Hill–Sachs remplissage and anterior Bankart repair: a retrospective controlled study including ultrasound evaluation of posterior capsulotenodesis and infraspinatus strength assessment. Am J Sports Med 2015;43:407414.

    • Search Google Scholar
    • Export Citation
  • 82.

    Longo UG, Rizzello G, Locher J et al.. Bone loss in patients with posterior gleno-humeral instability: a systematic review. Knee Surg Sports Traumatol Arthrosc 2016;24:612617.

    • Search Google Scholar
    • Export Citation
  • 83.

    Kowalsky MS, Levine WN. Traumatic posterior glenohumeral dislocation: classification, pathoanatomy, diagnosis, and treatment. Orthop Clin North Am 2008;39:519533, viii.

    • Search Google Scholar
    • Export Citation
  • 84.

    Rouleau DM, Hebert-Davies J. Incidence of associated injury in posterior shoulder dislocation: systematic review of the literature. J Orthop Trauma 2012;26:246251.

    • Search Google Scholar
    • Export Citation
  • 85.

    Moroder P, Plachel F, Tauber M et al.. Risk of engagement of bipolar bone defects in posterior shoulder instability. Am J Sports Med 2017;45:28352839.

    • Search Google Scholar
    • Export Citation
  • 86.

    Moroder P, Runer A, Kraemer M et al.. Influence of defect size and localization on the engagement of reverse Hill–Sachs lesions. Am J Sports Med 2015;43:542548.

    • Search Google Scholar
    • Export Citation
  • 87.

    Moroder P, Tauber M, Scheibel M et al.. Defect characteristics of reverse Hill–Sachs lesions. Am J Sports Med 2016;44:708714.

  • 88.

    Servien E, Walch G, Cortes ZE, Edwards TB, O’Connor DP. Posterior bone block procedure for posterior shoulder instability. Knee Surg Sports Traumatol Arthrosc 2007;15:11301136.

    • Search Google Scholar
    • Export Citation
  • 89.

    Levigne C, Garret J, Walch G. Posterior bone block for posterior instability. Knee Surg Sports Traumatol Arthrosc 2007;15:11301136.

  • 90.

    Levigne C, Walch G. Osteotomy and bone block techniques for posterior glenohumeral instability. In: Fu FH, Ticker JB, Imhoff AB, eds. An atlas of shoulder surgery. London: Martin Dunitz, 1998:4756.

    • Search Google Scholar
    • Export Citation
  • 91.

    Williams RJ, Strickland S, Cohen M, Altchek DW, Warren RF. Arthroscopic repair for traumatic posterior shoulder instability. Am J Sports Med 2003;31:203209.

    • Search Google Scholar
    • Export Citation