Clinical and radiological examination of bony-mediated shoulder instability

in EFORT Open Reviews
Authors:
Jakub StefaniakDepartment of Traumatology, Orthopaedics and Hand Surgery, Poznan University of Medical Sciences, Poznan, Poland
Sport Traumatology and Biomechanics Unit, Rehasport Clinic, Poznan University of Medical Sciences, Poznan, Poland

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Przemyslaw LubiatowskiSport Traumatology and Biomechanics Unit, Rehasport Clinic, Poznan University of Medical Sciences, Poznan, Poland

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Anna Maria KubickaInstitute of Zoology, Poznan University of Life Sciences, Poznan, Poland

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Anna WawrzyniakSport Traumatology and Biomechanics Unit, Rehasport Clinic, Poznan University of Medical Sciences, Poznan, Poland

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Joanna WałeckaSport Traumatology and Biomechanics Unit, Rehasport Clinic, Poznan University of Medical Sciences, Poznan, Poland

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Leszek RomanowskiDepartment of Traumatology, Orthopaedics and Hand Surgery, Poznan University of Medical Sciences, Poznan, Poland

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Jakub Stefaniak, Poznan University of Medical Sciences - Sport Trauma and Biomechanics Unit, Górecka 30, Poznan, Wielkopolskie 60201, Poland. Email: jakub.stefaniak@rehasport.pl
DOI:
https://doi.org/10.1302/2058-5241.5.200049
Volume/Issue:
Volume 5: Issue 11
Page Range:
815–827
Article Type:
Review Article
Online Publication Date:
13 Nov 2020
Copyright:
© 2020 The author(s) 2020
Open access

  • The coexistence of glenoid and humeral head bone defects may increase the risk of recurrence of instability after soft tissue repair.

  • Revealed factors in medical history such as male gender, younger age of dislocation, an increasing number of dislocations, contact sports, and manual work or epilepsy may increase the recurrence rate of instability.

  • In physical examination, positive bony apprehension test, catching and crepitations in shoulder movement may suggest osseous deficiency.

  • Anteroposterior and axial views allow for the detection of particular bony lesions in patients with recurrent anterior shoulder instability.

  • Computed Tomography (CT) with multiplanar reconstruction (MPR) and various types of 3D rendering in 2D (quasi-3D-CT) and 3D (true-3D-CT) space allows not only detection of glenoid and humeral bone defects but most of all their quantification and relations (engaging/not-engaging and on-track/off-track) in the context of bipolar lesion.

  • Magnetic resonance imaging (MRI) is increasingly developing and can provide an equally accurate measurement tool for bone assessment, avoiding radiation exposure for the patient.

Cite this article: EFORT Open Rev 2020;5:815-827. DOI: 10.1302/2058-5241.5.200049

Abstract

  • The coexistence of glenoid and humeral head bone defects may increase the risk of recurrence of instability after soft tissue repair.

  • Revealed factors in medical history such as male gender, younger age of dislocation, an increasing number of dislocations, contact sports, and manual work or epilepsy may increase the recurrence rate of instability.

  • In physical examination, positive bony apprehension test, catching and crepitations in shoulder movement may suggest osseous deficiency.

  • Anteroposterior and axial views allow for the detection of particular bony lesions in patients with recurrent anterior shoulder instability.

  • Computed Tomography (CT) with multiplanar reconstruction (MPR) and various types of 3D rendering in 2D (quasi-3D-CT) and 3D (true-3D-CT) space allows not only detection of glenoid and humeral bone defects but most of all their quantification and relations (engaging/not-engaging and on-track/off-track) in the context of bipolar lesion.

  • Magnetic resonance imaging (MRI) is increasingly developing and can provide an equally accurate measurement tool for bone assessment, avoiding radiation exposure for the patient.

Cite this article: EFORT Open Rev 2020;5:815-827. DOI: 10.1302/2058-5241.5.200049

Keywords: shoulder instability; glenoid track; glenoid bone loss; Hill–Sachs lesion

Introduction

The assessment of glenoid and humeral head bone defects is important in pre-operative decision making and planning. The presence of anterior glenoid bone loss and/or Hill–Sachs lesion (HSL) is common and may increase the risk of recurrence of instability after primary arthroscopic Bankart repair. The literature that evaluates the relationship between the bony lesions and the recurrence of the shoulder instability reports rates from 4% to 67% in shoulders without and with significant bone defects, respectively. 1 Tauber et al showed that 57% of 41 patients were re-operated on the recurrence of instability due to anterior glenoid bone loss. 2 Both glenoid and humeral side defects, but also factors such as hyperlaxity, increased the risk of recurrence. 3 Balg and Boileau, in 2007, formulated the Instability Severity Index Score (ISIScore) and included both glenoid and humeral head defects as two of the main risk factors of recurrence, awarding each item two points. Remaining factors are age at the time of surgery (less than 20 years old), competitive sports participation, contact sports, shoulder hyperlaxity, humeral and glenoid side defects. 4 The presence of just a single bony deficit with a combination of any other factor affects the decision making, suggesting coracoid transfer to address the instability. Osseous deficits are quite frequent in patients operated on for anterior shoulder instability. Boileau found bony Bankart in 37% of cases and 13% in the cohort had an attritional glenoid defect. 4 Sugaya et al showed that 50% of the shoulders with recurrent instability had an bony Bankart lesion and up to 40% of the glenoids demonstrated abnormal glenoid rim. 5 Hill–Sachs lesions have been confirmed in 65% to 93% of instability patients. It has been agreed that it is also the size of the defect that matters for the planning. However, there is no agreement on the size of glenoid lesion that may increase the risk of failed Bankart repair. Itoi et al presented that the anterior glenoid defect, which comprises at least 21% of superior–inferior glenoid length, would increase the failure rating of a Bankart procedure and limit the range of motion. 6 Burkhart et al revealed that glenoid bone loss amounting to 25% or more of glenoid diameter required bone grafting. 7 Nowadays, the meaning of percentage bone loss is controversial in the case of anterior glenoid defect and Hill–Sachs coexistence.

The purpose of this study is to review the current literature in the context of glenoid and humeral head bone loss in patients with chronic anterior shoulder instability. We have focused on both clinical and radiological evaluation of the patient. Obtaining an adequate patient history reveals factors that would be associated with a higher risk of the presence of a defect. However, it is the imaging and accurate assessment of the size and relations of bone defects that are crucial for further treatment.

Clinical examination

Clinical examination alone may raise a high suspicion of glenohumeral bone deficiency. 8 Obtaining an adequate patient history reveals factors that would be associated with a higher risk of the presence of a defect. Milano et al found that male gender and an increasing number of dislocations resulted in an increased odds ratio of glenoid defect occurrence (4.29 and 1.18, respectively). The odds ratio of critical bone defect was 9.5 times with an increasing number of dislocations and also affected the size of the defect. Other risk factors included younger age at first dislocation, contact sports and manual work. 9 Other conditions such as epilepsy may increase the recurrence rate of instability (69% versus 10% for the non-epileptic group). 10

Suspicion of a bony problem may also come from physical examination of the shoulder.

In 2008, Bushnell et al, 11 presented the concept of a bony apprehension test in patients with significant bone lesions in shoulder instability. The apprehension was examined at 45° abduction and 45° external rotation and correlated with pre-operative radiograph assessment of bone defects. In all cases in which the arthroscopic findings confirmed bone lesions (eight of 29), the bone apprehension test was positive (100% sensitivity) as well as in another three cases where only soft tissue lesions were found (specificity of 83%, positive predictive value 73% and negative predictive value 100%). Despite some limitations such as a small study group, the authors consider that the bony apprehension test can reliably screen patients with recurrent anterior shoulder instability. Other clinical signs, e.g. mechanical symptoms, have been reported, suggesting osseous deficiency: catching or crepitation on shoulder movements. 12

Imaging of glenohumeral joint

Radiography

Radiography is an inexpensive, easy to perform and widely available imaging modality used for the evaluation of the glenohumeral joint. Specific views allow detection of particular bony lesions in patients with recurrent anterior shoulder instability. Anteroposterior and axial views with various modifications have been described and both can detect humeral head and glenoid defects. Humeral head compression fracture localized on the posterolateral aspect, known as Hill–Sachs defect, was first described by Malgaign in 1855. 13 A full description and morphology publication were performed 85 years later by Harold A. Hill and Maurice D. Sachs. 14 It may be well visualized in the anterior-posterior (AP) view with the arm in adduction and internal or external rotation (Fig. 1).

Fig. 1
Fig. 1

Radiography: shoulder in AP view with external (a) and internal (b) rotation.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Glenoid morphology should be assessed in both the AP and axial views (Fig. 2). The AP view may show signs such as disruption of contour, anterior glenoid fracture or defect. Axial views may show osseous Bankart lesions, cliff sign or even blunted angle of anterior glenoid. In 1972, Rokous et al first described the West Point Axillary view for assessment of the anterior glenoid rim. 15 Some other views, such as the Bernageau view 16 or Stryker notch view, 17 were used in the diagnosis and evaluation of the Hill–Sachs defect and anterior glenoid rim.

Fig. 2
Fig. 2

Radiography: shoulder in AP view (a) and axial view (b), white arrow – displaced osseous fragment.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Standard radiological evaluation has shown various levels of accuracy and diagnostic value for detection of osseous lesions. In 2003, Itoi et al presented that radiographic assessment of anterior glenoid bone loss is a good screening tool for patients after anterior shoulder dislocation. The West Point view shows the anteroinferior part of the glenoid and is consequently better than the axial view, which projects only the anterior glenoid rim. 18 The Instability Severity Index Score (ISIS) relies on the radiographic appearance of anterior glenoid bone loss (loss of anterior subchondral sclerotic rim, as seen in the AP view) and humeral head (Hill–Sachs visible in the AP view in maximal external rotation). The ISIS did not, however, consider the exact percentage of glenoid bone loss and was not correlated with either computed tomography (CT) or magnetic resonance (MR) scanning. 4 Nevertheless, it has been proven to be reliable in one multi-centre study with an excellent value at 0.933 of the Interclass Correlation Coefficient (ICC). 19 Compared to CT scans, the reliability was satisfying in glenoid bone loss of 15% or more. However, analysis of Hill–Sachs lesion was not consistent in the context of ISIS. 20 Assessment of anterior glenoid bone loss in the AP view was rated as moderately sensitive (56% to 64%) but highly specific (100%.) 21 On the other hand, Bouliane et al showed the radiographic part of the ISIS failed to achieve a kappa score of 0.7 (mostly fair-to-moderate) for both an intra- and inter-rater reliability. The authors suggested using ISIS only with caution in preoperative planning. 22

Edwards et al analysed 160 radiographs of shoulders in 156 patients with chronic anterior instability with the use of anteroposterior and Bernageau views. Glenoid bone lesions diagnosed in the Bernageau view were found in 79% of radiographs and divided into three groups: fracture (41.3%), cliff sign (13.1%) and blunted angle (25%). Anteroposterior view with the arm in internal rotation was used to assess the presence of Hill–Sachs defect (73.1%) and fractures of the inferior glenoid rim (45.6%). 23

Rowe et al classified Hill–Sachs lesions based on their size in axillary view: mild (2 cm x 0.3cm), moderate (2–4 cm x 0.3–1 cm), and severe (4 cm > x > 1 cm). 24

Sommaire et al proposed the Hill–Sachs measurement in AP view with internal rotation (D/R ratio; D – notch depth; R – radius of humeral head) and glenoid bone loss assessment in the Bernageau view (D1/D2; D1– glenoid surface diameter of affected shoulder, D2 – glenoid surface diameter of healthy shoulder). These parameters were compared with the recurrence rate (15.6%) after arthroscopic Bankart repair. The authors showed that the risk of recurrence was significantly greater when the D/R ratio was higher or equal to 20%. 25

Computed tomography (CT)

CT ensures high resolution, allowing for multiplanar and 3D reconstruction with good quality. For this reason, CT is now a gold standard in the assessment of bone lesions in patients with chronic anterior shoulder instability. 26 The method allows not only for detection of the lesions but more importantly for their quantification. One major disadvantage of a CT scan, however, is the radiation exposure for the patient, and this may be a limitation in case of the need for repeated examinations. 27

Bishop et al showed that CT is more reliable in the assessment of glenoid bone loss than magnetic resonance imaging (MRI) or radiography. Moreover, 3D-CT was the most reliable but achieved only a moderate kappa value. 28 Kubicka et al compared 2D and 3D-CT in the assessment of glenoid bone loss and showed that 3D–CT reliability was nearly perfect in all measurements, even if performed by an inexperienced observer. 29 Stefaniak et al performed a similar study and proved that 3D-CT is also more reliable in humeral head and Hill–Sachs lesion evaluation with excellent values of ICC and the Minimal Detectable Change with 95% confidence (MDC95). 30

2D-CT, quasi-3D-CT and true-3D-CT

The term 3D-CT reconstruction may sometimes be misleading and has been erroneously used in papers since not all measurements are in fact done as 3D. 29,31,32 In true-3D-CT, measurements are set on a 3D model that can be freely rotated during the measuring process (Fig. 3c). 29 In this way, we minimize the error that arises during the incorrect or imprecise evaluation of the bone contour in a 2D image. This technique allows for full control in the space and highly accurate measurements.

Fig. 3
Fig. 3

(a) 2D-CT with multiplanar reconstruction (2D-CT–MPR); (b) quasi-3D-CT; (c) true-3D-CT.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Another method, quasi-3D is a 2D measurement based on a picture acquired from 3D reconstruction (measurements are not performed in 3D space) (Fig. 3b). Many authors use 3D reconstruction to make a 2D picture of the measuring object, for example an ‘en face’ glenoid view. In this case, we cannot rotate the object during measuring process and the risk of making a mistake can occur due to indistinct bone contour.

Another option is 2D-CT with multiplanar reconstruction (MPR) (Fig. 3a) in which we can set the 2D section of the measured object in frontal, sagittal and transverse planes.

A proper understanding of the methods used for measurement is crucial for comparative analyses. The authors urge clear definition of the measurement methods used in the studies and use of the proper nomenclature in order to avoid misunderstandings.

Glenoid evaluation

Glenoid bone defects in patients with recurrent anterior shoulder instability usually occur on the anterior glenoid rim between 2:30 and 4:20 on the clock face for the right glenoid. Saito et al found mean orientation of the defect at 3:01 o’clock, which is the direction with the least stability ratio 33 . Regarding the 38° anterior tilt of the glenoid in the sagittal plane relative to the trunk, the defect is oriented towards 4:17 in reference to the trunk. The measurements were performed on quasi-3D-CT. 32 Burkhart et al described the term ‘inverted pear-glenoid’ as the result of a large anterior glenoid bone defect that changes the shape of the glenoid from normal pear-shaped to inverted. 1 Moreover, Burkhart et al first proposed the term ‘bare spot’ as a central reference point to assess the percentage loss of anterior glenoid rim. The spot was evaluated arthroscopically as the centre of a circle that was defined by the margin of the postero-inferior glenoid contour. 7 The reliability of the bare spot as a central reference point of the glenoid has been questioned. Saintmard et al identified the bare spot in less than 48% of cases during arthroscopy and in only 26% with CT arthrography 34 . Two cadaveric studies assessed bare spot measurements and showed that the bare spot was eccentric in most of the cases, making it an unreliable landmark in glenoid assessment. 35,36

Surface measurement of the glenoid is probably the most popular method in clinical use and planning. The idea of a best-fit circle was developed by Sugaya et al on 3D-CT (quasi-3D-CT) to assess the percentage value of anterior glenoid bone loss. The area of the displaced osseous fragment was calculated as a percentage of the area of the best-fitting circle (Fig. 4a) 5 and in the other study, bone defect width calculated as a percentage of the diameter of the best-fitting circle (Fig. 4b). 35 Huysmans et al showed on a cadaveric study good inter- and intra-observer reliability of the Sugaya method. 36

Fig. 4
Fig. 4

Best-fit circle method presented by Sugaya et al (b/A x100%); (a) A – area of best-fit circle; b –area of displaced osseous fragment; (b) A – diameter of best-fit circle; b – bone defect width.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Baudi et al developed the Pico method (named in honour of Pico della Mirandola, the Italian philosopher), which is based on calculating the size of the defect in the affected shoulder as a percentage of the best-fit circle area of the contralateral glenoid on 2D-CT with MPR reconstruction (Fig. 5). 37 Evaluation of this method showed very good intra- and inter-observer reliability. 38

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Fig. 5
Fig. 5

Pico method developed by Baudi et al (b/Ax100%; b – area of defect; A –area of best-fit circle (of the contralateral glenoid) on 2D-CT with multiplanar reconstruction (MPR) (a) and quasi-3D-CT (5b).

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Linear indices have also been used for the quantification of glenoid deficiency. Gerber’s X index, presented in 2002 by Gerber and Nyffeler, showed the ratio of anterior glenoid bone defect length to maximum AP glenoid diameter. 39 This measurement method was assessed as simple and reproductive in daily practice 25 as well as being a reliable measuring method with the use of 2D-CT–MPR (Fig. 6). 40 The Glenoid index similarly proposed by Griffith et al 41 and Chuang et al, 42 is described as the ratio of the width of the injured glenoid to the width of the glenoid without bone defect. The measurements were presented on 2D-CT–MPR (Fig. 7) and quasi-3D-CT respectively and the authors proved that this CT measurement method has high sensitivity and specificity for detecting glenoid bone defects in comparison with arthroscopy. 43 Charousset et al found that the Griffith index showed good and excellent inter- and intra-observer reliability (ICC > 0.9). 20 Moreover, Griffith et al proved that parameters such as: maximum glenoid length (width-to-length ratio), glenoid cross-sectional area or the largest axial glenoid width were not useful for glenoid bone loss assessment. 41

disp-formula2-2058-5241.5.200049
disp-formula3-2058-5241.5.200049
Fig. 6
Fig. 6

Gerber’s index; A – diameter of best-fit circle; B – anterior glenoid bone defect length.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Fig. 7
Fig. 7

Glenoid index (A/Bx100%) A – diameter of injured glenoid; B –diameter of intact (contralateral) glenoid; (2D-CT–MPR).

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Barchilon et al presented an alternative method of assessment of the anterior glenoid rim with the use of the ratio between the depth from the centre of the best-fit circle to the edge of the glenoid defect and the radius of best-fit circle. 44 All measurements were performed on 3D-CT (t3D) (Fig. 8).

disp-formula4-2058-5241.5.200049
Fig. 8
Fig. 8

Barchillon et al.; d/R d – depth from the centre of the best-fit circle to the edge of the glenoid; R – radius of best-fit circle on 2D-CT–MPR (a) and quasi-3D-CT (b).

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Humeral head evaluation

Humeral measurement focuses on evaluation of the Hill–Sachs defect. The most common measurements include length, width, depth, volume, surface area, angle and location or orientation (Fig. 9).

Fig. 9
Fig. 9

Humeral head measurements of Hill–Sachs lesion (HSL); (a) a – best-fit circle, d – HSL depth, b – HSL width; (b) HSL orientation, the clock face, e, e’ – medial and lateral margins of HSL; (c) HSL location, b – HSL width, b’ – HSL length.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Saito et al showed that the orientation of the Hill–Sachs defect usually occurs between 6:46 and 8:56 on the clock face on the right humeral head. The mean orientation was 7:58 with the intertubercular groove at 12 o’clock. To estimate the anterior and posterior margins of the defect, the authors used a circle that best-fitted the humeral head surface. In vertical orientation, Hill–Sachs occurred between 0 mm and 24 mm from the top of the humeral head, whereas the bare area existed below 19 mm. Authors showed how to estimate the locations of the Hill–Sachs lesion and the bare area that overlapped with each other. In other words, if Hill–Sachs lesion extends below 19 mm from the top of the humeral head, it overlaps the bare area (Fig. 9c). The measurements were performed with the use of 2D-CT–MPR. 45

Kodali et al found that Hill–Sachs measurements can be reliably evaluated using a CT scan. Measurements in the sagittal and axial views were more accurate than in the coronal view. 46

Cho et al 47 assessed the orientation and location of the HSL with the use of the Hill–Sachs angle and bicipital and vertical angles, respectively. The Hill–Sachs angle was determined by two lines: the longitudinal axis of the humeral shaft and the axis of the deepest groove of the Hill–Sachs drawn in anteroposterior view on 3D-CT (quasi-3D-CT) (Fig. 10). To estimate the location, the bicipital angle was calculated in the axial view of 2D-CT–MPR, between the line connecting the best-fit circle centre with the bicipital groove and a line drawn from the best-fit circle to the centre of the Hill–Sachs lesion. The vertical angle was estimated in the coronal view of 2D-CT–MPR, between the centre vertical line of the humeral head and the line drawn from the centre of the HSL to the centre of the best-fit circle.

Fig. 10
Fig. 10

Hill–Sachs angle; A – axis of the deepest groove of the Hill–Sachs; B- longitudinal axis of humeral shaft.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Bipolar evaluation of glenoid and humeral defects in CT

Recently, research focused not only on the size of a single defect but also on the interplay of both the anterior glenoid defect and HSL. Therefore, the terms engaging versus non-engaging or on-track versus off-track lesions have been introduced.

Engaging defects

Burkhart et al first presented the term ‘engaging’ Hill–Sachs, which means that the size and position of the Hill–Sachs cause its engagement with the anterior rim of the inverted pear glenoid in the athletic arm position (90° of abduction and 0–135° of external rotation). 1 They found that engaging defects had the worst prognosis when treated by arthroscopic labral stabilization. 1 On the other hand, different authors concluded that all defects have to engage so that the dislocation can occur, implying that the pathology may be over-diagnosed. Kurokawa et al introduced the term ‘true engaging HSL’, as one that occurs during arthroscopic examination even after Bankart repair, or when the HSL extends over the glenoid track. 48 The authors showed that the width and depth of the engaging Hill–Sachs were significantly larger and located more horizontal to the humeral head shaft than non-engaging lesions. 47 Kurokawa et al proposed two types of engaging Hill–Sachs: wide and large and the second, narrow but medially located. In an analysis of 200 CT scans of 100 patients with unilateral shoulder instability, the engaging Hill–Sachs was found in 7% of patients (2D-CT–MPR and 2D-3D–CT). 48

Glenoid track – on-track/off-track evaluation

Yamamoto et al presented the concept of glenoid track, which is a zone of contact between the glenoid and the articular surface of the humeral head based on a cadaver model. The width of the glenoid track was found to account for 84% of glenoid width. In the case of bone loss in the anterior glenoid rim, the glenoid track width decreases accordingly. Results were compared with 3D-CT measurements (t3D-CT) and this proved to be the same path of glenoid shift. 49 The calculation was clarified by Omori et al, who proposed a glenoid track width equal to 83% of glenoid width. The authors justified this with a younger group of patients with a greater range of motion in vivo than the cadaveric specimens used in the previous study. 50

The concept of ‘engaging and non-engaging’ Hill–Sachs lesions was adopted by Di Giacomo et al as ‘on-track and off-track’ lesions 51 . In on-track lesions, HSL falls within the margins of the glenoid track, whereas in off-track, Hill–Sachs extends its medial margin beyond the track. Assessment of the on-track/off-track status of HSL may be performed during an arthroscopic procedure and based on analysis of 3D-CT (quasi-3D-CT):

  1. The glenoid bone loss is evaluated in an ‘en face’ view of the glenoid (Fig. 11b).

  2. The value of the glenoid track of an intact glenoid (GTint) is calculated with the use of the contralateral shoulder as a reference. The authors did not propose a way of evaluation in case of bilateral bone loss. 51

    The width of the glenoid track is 83% of the width of the intact (contralateral) glenoid (D).

    disp-formula5-2058-5241.5.200049

  3. To calculate the glenoid track width of the affected glenoid (GTaf), the width of the defect (d) is subtracted from the glenoid track width of the intact glenoid.

    disp-formula6-2058-5241.5.200049

  4. The assessment of on-track/off-track is performed on a posterior view of the humeral head with the use of two lines. The distance between the lines is the width of the glenoid track in this case (GTaf):

    1. line of the medial margin of rotator cuff attachments (R)

    2. line that indicates the medial margin of the glenoid track of the affected shoulder (G2)

  5. If the medial margin line of HSL extends beyond the glenoid track (L2), it is called ‘off-track’, otherwise, it is ‘on-track’ if it lies between the lines.

All measurements are presented in Fig. 11.

Fig. 11
Fig. 11

On-track/off-track measurements; (a) R- line of medial margin of rotator cuff attachments; G2 – line of medial margin of glenoid track of affected shoulder; G1 – line of medial margin of glenoid track of intact shoulder; HIS – Hill–Sachs Interval; BB – bone bridge; d – width of anterior glenoid bone defect; GTaf – width of glenoid track of affected shoulder; GTint – width of glenoid track of intact shoulder; (b) D – width of intact glenoid; d – width of glenoid bone defect.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

Di Giacomo et al categorized patients based on glenoid defect size and HLS engagement: 1st group, < 25% of glenoid defect with on-track H-S; 2nd group, < 25% of glenoid defect with off-track H-S; 3rd group, ⩾ 25% glenoid lesion with on-track H-S and 4th group, ⩾ 25% glenoid bone loss with off-track. Using these categories, the authors determined a surgical treatment paradigm useful in surgical planning (Table 1.). 51

Table 1.

Surgical treatment paradigm as suggested by Di Giacomo et al 51

On-track HSL Off-track HSL
< 25% glenoid bone loss Arthroscopic Bankart repair Arthroscopic Bankart repair + HSL remplissage
⩾ 25% glenoid bone loss Latarjet procedure Latarjet procedure + humeral-sided procedure

(bone graft or remplissage)

Yamamoto et al showed that patients with on-track lesions but with 75% or more of Hill – Sachs occupancy had a significantly worse Western Ontario Shoulder Instability Index (WOSI) score. The Hill–Sachs occupancy was evaluated on 3D-CT and defined as Hill – Sachs interval/glenoid track width x 100% (HSL interval – distance from the medial margin of the rotator cuff attachments to the medial margin of the HSL). 52

Schneider et al assessed the intra- and inter-observer reliability of glenoid track measurements on 3D-CT (2D-3D–CT). The evaluation of glenoid bone loss had good inter- and intra-observer agreement (in 90% and 94% to 96% of cases, respectively). However, measurement showed poorer inter-observer reliability for on-track/off-track classification (72%) and moderate inter-observer reliability regarding treatment classification (65%). The authors concluded that glenoid assessment is reliable and reproducible, but Hill–Sachs evaluation had a high level of variability and only moderate agreement between observers. 53 Stefaniak et al assessed 45 patients after failed arthroscopic Bankart repair in the context of on-track/off-track assessment. Glenoid track evaluation showed 38 patients (85%) with ‘off-track’ Hill–Sachs lesion but seven patients (15%) with ‘on-track’ lesions. The authors showed that the on-track/off-track concept was unable to fully predict instability recurrence following isolated Bankart repair, especially in patients with less glenoid bone loss. 54 In 2020, Di Giacomo proposed the modification of the ISIScore with the use of on-track/off-track assessment. In the Glenoid Track Instability Management Score (GTIMS), ‘off-track’ Hill–Sachs is awarded four points, while on-track is not awarded any points at all, regardless of the size of glenoid bone loss and Hill–Sachs lesion. The authors showed the significant differences in distribution of indications following treatment, based on ISIS versus GTIMS. 55

Magnetic resonance imaging

MRI is widely used in the assessment of shoulder pathology. MRI has several advantages. First of all:

  • it does not expose the patient to any radiation, thus allowing safer repeated examinations when necessary;

  • it is the most useful modality for soft tissue evaluation and assessment of many comorbidities. It has been shown to be highly accurate for evaluation of labral tears 56 and cartilage lesions, especially when enhanced with arthrography.

However:

  • it is much more expensive;

  • it is less available;

  • it takes longer to acquire and depends on technical quality;

  • it is not available for every patient (claustrophobia, pacemaker, some implants);

  • most of all, standard MRI has been less accurate for bone assessment in comparison to CT. 57

Interestingly, more recent advancements have brought significant improvement in this area. Stillwater et al demonstrated the high accuracy of 3D-MRI (isotropic VIBE sequence), which is equivalent to 3D-CT (2D-3D-CT). The measurements of glenoid and Hill–Sachs bone loss, for example, the height and width of the humeral head and glenoid and percentage of glenoid and humeral head bone loss were compared and showed that differences were not statistically significant. 58

Yanke et al compared the 3D-MRI (quasi-3D-MRI, not in 3D space) (1,5 and 3 teslas) with quasi-3D-CT in cadaveric models. The authors showed that 3D-MRI measurements correlate with CT and provide a reproducible method in the evaluation of anterior glenoid bone defects. 59 Fernandes de Mello et al showed similar results in glenoid assessment between 3D Zero Echo Times (ZTE) MRI and 3D-CT. However, similar to other studies, the authors compared quasi-3D-MRI with quasi-3D-CT (not in 3D space). 60 ZTE MRI provides similar images to CT contrast for bone and better visualization of osseous features when compared with standard MRI. 61

Metzger et al compared the glenohumeral engagement on a magnetic resonance arthrogram with multiplanar reconstruction (MRA–MPR) with clinical evaluation during shoulder arthroscopy. The mean bone loss was 7.6% and 84.5% of patients with off-track lesion showing clinical evidence of engagement too. The authors assessed that pre-operative glenohumeral measurements on MRA–MPR can be used effectively to predict the risk of engagement. 62

Other results seem to support the evidence that MRI may be a reliable measure and could be used in the assessment of glenoid bone loss 63 and the existence of glenoid track, 50 nearly to a standard identical to CT.

Conclusions

Glenoid and glenohumeral defects commonly exist in anterior shoulder instability and affect clinical results. This means every orthopaedic surgeon has to have the ability to both diagnose them and, in the case of surgical planning, also measure them. Clinical examination may raise suspicion of their presence based mostly on the identification of risk factors from the patient history. Diagnostic algorithm should start with precise clinical examination.

Basic radiography with at least two views (true AP with the arm in internal or external rotation and axial view) is helpful in the identification of osseous lesions and is required to exclude other pathologies such as fractures or humeral head dislocation.

CT, especially with true 3D reconstruction, seems to be the golden standard for identification and quantification of boney lesions of the glenoid and humeral head. It is also useful in the assessment of on-track or off-track relations between a Hill–Sachs lesion and an anterior glenoid bone defect.

The use of MR in the evaluation of glenoid and humeral head bone defects is developing increasingly and can provide an equally accurate measurement tool for bone assessment while avoiding excessive radiation exposure for the patient.

Finally, the authors propose the diagnostic algorithm for bony-mediated shoulder instability. Evaluation should start with clinical examination and basic radiography with at least two views: true AP and an axial view. For more accurate evaluation in pre-operative surgical planning, ‘true’ 3D CT is recommended. 3D reconstruction with the use of MR is also applicable, but high-resolution and good-quality images may be required for proper bone evaluation (Fig. 12).

Fig. 12
Fig. 12

Algorithmic approach to clinical and radiological evaluation of bone deficiency in shoulder instability.

Citation: EFORT Open Reviews 5, 11; 10.1302/2058-5241.5.200049

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

PL reports board membership of the Rehasport Clinic, employment by Rehasport Clinic, University of Medical Sciences, payment for lectures including service on speakers’ bureaus from Smith&Nephew and Arthrex, payment for development of educational presentations from Smith&Nephew and is an Associate Editor of EFORT Open Reviews, all outside the submitted work.

The other authors declare no conflict of interest relevant to this 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.

OA licence text

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.

References

  • 1.↑

    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; 16:677-694 .

    • Search Google Scholar
    • Export Citation
  • 2.↑

    Tauber M , Resch H , Forstner R , Raffl M , Schauer J . Reasons for failure after surgical repair of anterior shoulder instability. J Shoulder Elbow Surg 2004; 13:279-285 .

    • Search Google Scholar
    • Export Citation
  • 3.↑

    Boileau P , Villalba M , Héry Jy , Balg F , Ahrens P . Risk factors for recurrence of shoulder instability after arthroscopic Bankart repair. J Bone Joint Surg Am 2006 Aug;88:1755-1763 .

    • Search Google Scholar
    • Export Citation
  • 4.↑

    Balg F , Boileau P . The instability severity index score: a simple pre-operative score to select patients for arthroscopic or open shoulder stabilisation. J Bone Jt Surg – Ser B 2007; 89:1470–1477 .

    • Search Google Scholar
    • Export Citation
  • 5.↑

    Sugaya H. , Moriishi J , Dohi M , Kon Y , Tsuchiya A . Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg Am 2003 May;85:878-884 .

    • Search Google Scholar
    • Export Citation
  • 6.↑

    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 Jt Surg - Ser A 2000 Jan;82:35–46 .

    • Search Google Scholar
    • Export Citation
  • 7.↑

    Burkhart SS , Debeer JF , Tehrany AM , Parten PM . Quantifying glenoid bone loss arthroscopically in shoulder instability. Arthroscopy 2002; 18:488-491 .

    • Search Google Scholar
    • Export Citation
  • 8.↑

    Lubiatowski P , Stefaniak J & Kubicka AM et al. Evaluation of bone defects in shoulder instability. Issue Rehabil Orthop Neurophysiol Sport Promot 2018; 23:71-82 .

    • Search Google Scholar
    • Export Citation
  • 9.↑

    Milano G , Grasso A & Russo A et al. Analysis of risk factors for glenoid bone defect in anterior shoulder instability. Am J Sports Med 2011; 39:1870-1876 .

    • Search Google Scholar
    • Export Citation
  • 10.↑

    Thangarajah T , Lambert SM . Management of recurrent shoulder instability in patients with epilepsy. J Shoulder Elbow Surg 2016; 25:1376-1384 .

    • Search Google Scholar
    • Export Citation
  • 11.↑

    Bushnell BD , Creighton RA , Herring MM . The bony apprehension test for instability of the shoulder: a prospective pilot analysis. Arthroscopy 2008; 24:974-982 .

    • Search Google Scholar
    • Export Citation
  • 12.↑

    Provencher MT , Frank RM & Leclere LE et al. The Hill-Sachs lesion: diagnosis, classification, and management. J Am Acad Orthop Surg 2012; 20:242-252 .

    • Search Google Scholar
    • Export Citation
  • 13.↑

    Malgaigne J . Traité des fractures et des luxations. Paris: JB Baillière; 1855 .

  • 14.↑

    Hill HA , Sachs MD . The grooved defect of the humeral head. Radiology 1940; 35:690-700 .

  • 15.↑

    Rokous JR , Feagin JA , Abbott HG . Modified axillary roentgenogram. A useful adjunct in the diagnosis of recurrent instability of the shoulder. Clin Orthop Relat Res 1972; 82:84-86 .

    • Search Google Scholar
    • Export Citation
  • 16.↑

    Bernageau J , Patte D , Debeyre J , Ferrane J . Value of the glenoid profil in recurrent luxations of the shoulder. Rev Chir Orthop Repar Appar Mot 1976; 62(suppl):142-147 .

    • Search Google Scholar
    • Export Citation
  • 17.↑

    Rozing PM , de Bakker HM , Obermann WR . Radiographic views in recurrent anterior shoulder dislocation. Comparison of six methods for identification of typical lesions. Acta Orthop Scand 1986; 57:328-330 .

    • Search Google Scholar
    • Export Citation
  • 18.↑

    Itoi E , Lee SB , Amrami KK , Wenger DE , An KN . Quantitative assessment of classic anteroinferior bony Bankart lesions by radiography and computed tomography. Am J Sports Med 2003; 31:112-118 .

    • Search Google Scholar
    • Export Citation
  • 19.↑

    Rouleau DM , Hébert-Davies J , Djahangiri A , Godbout V , Pelet S , Balg F . Validation of the instability shoulder index score in a multicenter reliability study in 114 consecutive cases. Am J Sports Med 2013; 41:278-282 .

    • Search Google Scholar
    • Export Citation
  • 20.↑

    Charousset C , Beauthier V , Bellaïche L , Guillin R , Brassart N , Thomazeau H ; French Arthroscopy Society. Can we improve radiological analysis of osseous lesions in chronic anterior shoulder instability? Orthop Traumatol Surg Res 2010; 96(suppl):S88-S93 .

    • Search Google Scholar
    • Export Citation
  • 21.↑

    Jankauskas L , Rüdiger HA , Pfirrmann CWA , Jost B , Gerber C . Loss of the sclerotic line of the glenoid on anteroposterior radiographs of the shoulder: a diagnostic sign for an osseous defect of the anterior glenoid rim. J Shoulder Elbow Surg 2010; 19:151-156 .

    • Search Google Scholar
    • Export Citation
  • 22.↑

    Bouliane MJ , Chan H & Kemp K et al. The intra- and inter-rater reliability of plain radiographs for Hill-Sachs and bony glenoid lesions: evaluation of the radiographic portion of the instability severity index score. Shoulder Elbow 2013; 5:33-38 .

    • Search Google Scholar
    • Export Citation
  • 23.↑

    Edwards TB , Boulahia A , Walch G . Radiographic analysis of bone defects in chronic anterior shoulder instability. Arthroscopy 2003; 19:732-739 .

    • Search Google Scholar
    • Export Citation
  • 24.↑

    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; 66:159-168 .

    • Search Google Scholar
    • Export Citation
  • 25.↑

    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; 98:514-519 .

    • Search Google Scholar
    • Export Citation
  • 26.↑

    Lansdown DA , Dawe R , Cvetanovich GL , Verma NN , Cole BJ & Bach BR et al. Automated 3D MRI allows for accurate evaluation of glenoid bone loss as compared to 3D CT. Arthroscopy 2019 Mar;35:734-740 .

    • Search Google Scholar
    • Export Citation
  • 27.↑

    Sodickson A , Baeyens PF & Andriole KP et al. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults. Radiology 2009; 251:175-184 .

    • Search Google Scholar
    • Export Citation
  • 28.↑

    Bishop JY , Jones GL , Rerko MA , Donaldson C ; MOON Shoulder Group. 3-D CT is the most reliable imaging modality when quantifying glenoid bone loss. Clin Orthop Relat Res 2013; 471:1251-1256 .

    • Search Google Scholar
    • Export Citation
  • 29.↑

    Kubicka AM , Stefaniak J & Lubiatowski P et al. Reliability of measurements performed on two dimensional and three dimensional computed tomography in glenoid assessment for instability. Int Orthop 2016; 40:2581-2588 .

    • Search Google Scholar
    • Export Citation
  • 30.↑

    Stefaniak J , Kubicka AM , Wawrzyniak A , Romanowski L , Lubiatowski P . Reliability of humeral head measurements performed using two- and three-dimensional computed tomography in patients with shoulder instability. Int Orthop 2020 Jul 26. doi: [Epub ahead of print].

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31.↑

    Diederichs G , Seim H & Meyer H et al. CT-based patient-specific modeling of glenoid rim defects: a feasibility study. AJR Am J Roentgenol 2008; 191:1406-1411 .

    • Search Google Scholar
    • Export Citation
  • 32.↑

    Chuang TY , Adams CR , Burkhart SS . Use of preoperative three-dimensional computed tomography to quantify glenoid bone loss in shoulder instability. Arthroscopy 2008; 24:376-382 .

    • Search Google Scholar
    • Export Citation
  • 33.↑

    Saito H , Itoi E , Sugaya H , Minagawa H , Yamamoto N , Tuoheti Y . Location of the glenoid defect in shoulders. Am J Sports Med 2005; 33:889-93.

    • Search Google Scholar
    • Export Citation
  • 34.↑

    Saintmard B , Lecouvet F , Rubini A , Dubuc J-E . Is the bare spot a valid landmark for glenoid evaluation in arthroscopic Bankart surgery? Acta Orthop Belg 2009; 75:736-742 .

    • Search Google Scholar
    • Export Citation
  • 35.↑

    Aigner F , Longato S , Fritsch H , Kralinger F . Anatomical considerations regarding the ‘bare spot’ of the glenoid cavity. Surg Radiol Anat 2004; 26:308-311 .

    • Search Google Scholar
    • Export Citation
  • 36.↑

    Huysmans PE , Haen PS , Kidd M , Dhert WJ , Willems JW . The shape of the inferior part of the glenoid: a cadaveric study. J Shoulder Elbow Surg 2006; 15:759-763 .

    • Search Google Scholar
    • Export Citation
  • 37.↑

    Sugaya H , Moriishi J , Kanisawa I , Tsuchiya A . Arthroscopic osseous Bankart repair for chronic recurrent traumatic anterior glenohumeral instability. J Bone Jt Surg - Ser A 2005; 87:1752–60.

    • Search Google Scholar
    • Export Citation
  • 38.↑

    Baudi P , Righi P & Bolognesi D et al. How to identify and calculate glenoid bone deficit. Chir Organi Mov 2005; 90:145-152 .

  • 39.↑

    Magarelli N , Milano G , Sergio P , Santagada DA , Fabbriciani C , Bonomo L . Intra-observer and interobserver reliability of the ‘Pico’ computed tomography method for quantification of glenoid bone defect in anterior shoulder instability. Skeletal Radiol 2009; 38:1071-1075 .

    • Search Google Scholar
    • Export Citation
  • 40.↑

    Gerber C , Nyffeler RW . Classification of glenohumeral joint instability. Clin Orthop Relat Res 2002; 400:65-76 .

  • 41.↑

    Maqdes A , Chammai Y & Lengert R et al. The intra- and inter-observer reliability of the CT-scan based X index to quantify glenoid bone loss in chronic anterior shoulder instability and its impact on decision making. Eur J Orthop Surg Traumatol 2015; 25:699-703 .

    • Search Google Scholar
    • Export Citation
  • 42.↑

    Griffith JF , Antonio GE , Tong CWC , Ming CK . Anterior shoulder dislocation: quantification of glenoid bone loss with CT. AJR Am J Roentgenol 2003; 180:1423-1430 .

    • Search Google Scholar
    • Export Citation
  • 43.↑

    Griffith JF , Yung PSH , Antonio GE , Tsang PH , Ahuja AT , Chan KM . CT compared with arthroscopy in quantifying glenoid bone loss. AJR Am J Roentgenol 2007; 189:1490-1493 .

    • Search Google Scholar
    • Export Citation
  • 44.↑

    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; 37:731-736 .

    • Search Google Scholar
    • Export Citation
  • 45.↑

    Saito H , Itoi E , Minagawa H , Yamamoto N , Tuoheti Y , Seki N . Location of the Hill-Sachs lesion in shoulders with recurrent anterior dislocation. Arch Orthop Trauma Surg 2009; 129:1327-1334 .

    • Search Google Scholar
    • Export Citation
  • 46.↑

    Kodali P , Jones MH , Polster J , Miniaci A , Fening SD . Accuracy of measurement of Hill-Sachs lesions with computed tomography. J Shoulder Elbow Surg 2011; 20:1328-1334 .

    • Search Google Scholar
    • Export Citation
  • 47.↑

    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; 39:2389-2395 .

    • Search Google Scholar
    • Export Citation
  • 48.↑

    Kurokawa D , Yamamoto N & Nagamoto H et al. The prevalence of a large Hill-Sachs lesion that needs to be treated. J Shoulder Elbow Surg 2013; 22:1285-1289 .

    • Search Google Scholar
    • Export Citation
  • 49.↑

    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 glenoid track. J Shoulder Elbow Surg 2007; 16:649-656 .

    • Search Google Scholar
    • Export Citation
  • 50.↑

    Omori Y , Yamamoto N & Koishi H et al. Measurement of the glenoid track in vivo as investigated by 3-dimensional motion analysis using open MRI. Am J Sports Med.2014; 42:1290-1295 .

    • Search Google Scholar
    • Export Citation
  • 51.↑

    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; 30:90-98 .

    • Search Google Scholar
    • Export Citation
  • 52.↑

    Yamamoto N , Shinagawa K , Hatta T , Itoi E . Peripheral-track and central-track Hill-Sachs lesions: a new concept of assessing an on-track lesion. Am J Sports Med 2020; 48:33-38 .

    • Search Google Scholar
    • Export Citation
  • 53.↑

    Schneider AK , Hoy GA & Ek ET et al. Interobserver and intraobserver variability of glenoid track measurements. J Shoulder Elbow Surg 2017; 26:573-579 .

    • Search Google Scholar
    • Export Citation
  • 54.↑

    Stefaniak J , Olmos M , Johanston T , Boileau P . Arthroscopic Bankart repair: is on-track/off-track concept enough to predict failures? Shoulder Concepts 2020. Nice Shoul. in press.

    • Search Google Scholar
    • Export Citation
  • 55.↑

    Di Giacomo G , Peebles LA & Pugliese M et al. Glenoid track instability management score: radiographic modification of the Instability Severity Index Score. Arthroscopy 2020; 36:56-67 .

    • Search Google Scholar
    • Export Citation
  • 56.↑

    Ajuied A , McGarvey CP , Harb Z , Smith CC , Houghton RP , Corbett SA . Diagnosis of glenoid labral tears using 3-tesla MRI vs. 3-tesla MRA: a systematic review and meta-analysis. Arch Orthop Trauma Surg 2018; 138:699-709 .

    • Search Google Scholar
    • Export Citation
  • 57.↑

    Friedman LGM , Ulloa SA , Braun DT , Saad HA , Jones MH , Miniaci AA . Glenoid bone loss measurement in recurrent shoulder dislocation: assessment of measurement agreement between CT and MRI. Orthop J Sports Med 2014; 2:2325967114549541 .

    • Search Google Scholar
    • Export Citation
  • 58.↑

    Stillwater L , Koenig J , Maycher B , Davidson M . 3D-MR vs. 3D-CT of the shoulder in patients with glenohumeral instability. Skeletal Radiol 2017; 46:325-331 .

    • Search Google Scholar
    • Export Citation
  • 59.↑

    Yanke AB , Shin JJ & Pearson I et al. Three-dimensional magnetic resonance imaging quantification of glenoid bone loss is equivalent to 3-dimensional computed tomography quantification: cadaveric study. Arthroscopy 2017; 33:709-715 .

    • Search Google Scholar
    • Export Citation
  • 60.↑

    Fernandes de Mello RA , Ma Y & Ashir A et al. 3D Zero Echo Time (ZTE) MRI versus 3D CT for glenoid bone assessment. Arthroscopy 2020; 36:2391-2400 .

    • Search Google Scholar
    • Export Citation
  • 61.↑

    Breighner RE , Endo Y , Konin GP , Gulotta LV , Koff MF , Potter HG . Technical developments: Zero Echo Time imaging of the shoulder: enhanced osseous detail by using MR imaging. Radiology 2018; 286:960-966 .

    • Search Google Scholar
    • Export Citation
  • 62.↑

    Metzger PD , Barlow B , Leonardelli D , Peace W , Solomon DJ , Provencher MT . Clinical application of the “glenoid track” concept for defining humeral head engagement in anterior shoulder instability: A preliminary report. Orthop J Sports Med 2013; 1(2):2325967113496213 .

    • Search Google Scholar
    • Export Citation
  • 63.↑

    Gyftopoulos S , Yemin A & Mulholland T et al. 3DMR osseous reconstructions of the shoulder using a gradient-echo based two-point Dixon reconstruction: a feasibility study. Skeletal Radiol 2013; 42:347-352 .

    • Search Google Scholar
    • Export Citation

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Online ISSN:
2058-5241
Copyright:
© 2020 The author(s) 2020
Article Type:
Review Article
Page Range:
815–827
Published Online:
13 Nov 2020
Keywords:
shoulder instability; glenoid track; glenoid bone loss; Hill–Sachs lesion
  • Fig. 1
    View in gallery
    Fig. 1

    Radiography: shoulder in AP view with external (a) and internal (b) rotation.

  • Fig. 2
    View in gallery
    Fig. 2

    Radiography: shoulder in AP view (a) and axial view (b), white arrow – displaced osseous fragment.

  • Fig. 3
    View in gallery
    Fig. 3

    (a) 2D-CT with multiplanar reconstruction (2D-CT–MPR); (b) quasi-3D-CT; (c) true-3D-CT.

  • Fig. 4
    View in gallery
    Fig. 4

    Best-fit circle method presented by Sugaya et al (b/A x100%); (a) A – area of best-fit circle; b –area of displaced osseous fragment; (b) A – diameter of best-fit circle; b – bone defect width.

  • Fig. 5
    View in gallery
    Fig. 5

    Pico method developed by Baudi et al (b/Ax100%; b – area of defect; A –area of best-fit circle (of the contralateral glenoid) on 2D-CT with multiplanar reconstruction (MPR) (a) and quasi-3D-CT (5b).

  • Fig. 6
    View in gallery
    Fig. 6

    Gerber’s index; A – diameter of best-fit circle; B – anterior glenoid bone defect length.

  • Fig. 7
    View in gallery
    Fig. 7

    Glenoid index (A/Bx100%) A – diameter of injured glenoid; B –diameter of intact (contralateral) glenoid; (2D-CT–MPR).

  • Fig. 8
    View in gallery
    Fig. 8

    Barchillon et al.; d/R d – depth from the centre of the best-fit circle to the edge of the glenoid; R – radius of best-fit circle on 2D-CT–MPR (a) and quasi-3D-CT (b).

  • Fig. 9
    View in gallery
    Fig. 9

    Humeral head measurements of Hill–Sachs lesion (HSL); (a) a – best-fit circle, d – HSL depth, b – HSL width; (b) HSL orientation, the clock face, e, e’ – medial and lateral margins of HSL; (c) HSL location, b – HSL width, b’ – HSL length.

  • Fig. 10
    View in gallery
    Fig. 10

    Hill–Sachs angle; A – axis of the deepest groove of the Hill–Sachs; B- longitudinal axis of humeral shaft.

  • Fig. 11
    View in gallery
    Fig. 11

    On-track/off-track measurements; (a) R- line of medial margin of rotator cuff attachments; G2 – line of medial margin of glenoid track of affected shoulder; G1 – line of medial margin of glenoid track of intact shoulder; HIS – Hill–Sachs Interval; BB – bone bridge; d – width of anterior glenoid bone defect; GTaf – width of glenoid track of affected shoulder; GTint – width of glenoid track of intact shoulder; (b) D – width of intact glenoid; d – width of glenoid bone defect.

  • Fig. 12
    View in gallery
    Fig. 12

    Algorithmic approach to clinical and radiological evaluation of bone deficiency in shoulder instability.

Fig. 1

Radiography: shoulder in AP view with external (a) and internal (b) rotation.
Fig. 2

Radiography: shoulder in AP view (a) and axial view (b), white arrow – displaced osseous fragment.
Fig. 3

(a) 2D-CT with multiplanar reconstruction (2D-CT–MPR); (b) quasi-3D-CT; (c) true-3D-CT.
Fig. 4

Best-fit circle method presented by Sugaya et al (b/A x100%); (a) A – area of best-fit circle; b –area of displaced osseous fragment; (b) A – diameter of best-fit circle; b – bone defect width.
Fig. 5

Pico method developed by Baudi et al (b/Ax100%; b – area of defect; A –area of best-fit circle (of the contralateral glenoid) on 2D-CT with multiplanar reconstruction (MPR) (a) and quasi-3D-CT (5b).
Fig. 6

Gerber’s index; A – diameter of best-fit circle; B – anterior glenoid bone defect length.
Fig. 7

Glenoid index (A/Bx100%) A – diameter of injured glenoid; B –diameter of intact (contralateral) glenoid; (2D-CT–MPR).
Fig. 8

Barchillon et al.; d/R d – depth from the centre of the best-fit circle to the edge of the glenoid; R – radius of best-fit circle on 2D-CT–MPR (a) and quasi-3D-CT (b).
Fig. 9

Humeral head measurements of Hill–Sachs lesion (HSL); (a) a – best-fit circle, d – HSL depth, b – HSL width; (b) HSL orientation, the clock face, e, e’ – medial and lateral margins of HSL; (c) HSL location, b – HSL width, b’ – HSL length.
Fig. 10

Hill–Sachs angle; A – axis of the deepest groove of the Hill–Sachs; B- longitudinal axis of humeral shaft.
Fig. 11

On-track/off-track measurements; (a) R- line of medial margin of rotator cuff attachments; G2 – line of medial margin of glenoid track of affected shoulder; G1 – line of medial margin of glenoid track of intact shoulder; HIS – Hill–Sachs Interval; BB – bone bridge; d – width of anterior glenoid bone defect; GTaf – width of glenoid track of affected shoulder; GTint – width of glenoid track of intact shoulder; (b) D – width of intact glenoid; d – width of glenoid bone defect.
Fig. 12

Algorithmic approach to clinical and radiological evaluation of bone deficiency in shoulder instability.
  • 1.

    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; 16:677-694 .

    • Search Google Scholar
    • Export Citation
  • 2.

    Tauber M , Resch H , Forstner R , Raffl M , Schauer J . Reasons for failure after surgical repair of anterior shoulder instability. J Shoulder Elbow Surg 2004; 13:279-285 .

    • Search Google Scholar
    • Export Citation
  • 3.

    Boileau P , Villalba M , Héry Jy , Balg F , Ahrens P . Risk factors for recurrence of shoulder instability after arthroscopic Bankart repair. J Bone Joint Surg Am 2006 Aug;88:1755-1763 .

    • Search Google Scholar
    • Export Citation
  • 4.

    Balg F , Boileau P . The instability severity index score: a simple pre-operative score to select patients for arthroscopic or open shoulder stabilisation. J Bone Jt Surg – Ser B 2007; 89:1470–1477 .

    • Search Google Scholar
    • Export Citation
  • 5.

    Sugaya H. , Moriishi J , Dohi M , Kon Y , Tsuchiya A . Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg Am 2003 May;85:878-884 .

    • Search Google Scholar
    • Export Citation
  • 6.

    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 Jt Surg - Ser A 2000 Jan;82:35–46 .

    • Search Google Scholar
    • Export Citation
  • 7.

    Burkhart SS , Debeer JF , Tehrany AM , Parten PM . Quantifying glenoid bone loss arthroscopically in shoulder instability. Arthroscopy 2002; 18:488-491 .

    • Search Google Scholar
    • Export Citation
  • 8.

    Lubiatowski P , Stefaniak J & Kubicka AM et al. Evaluation of bone defects in shoulder instability. Issue Rehabil Orthop Neurophysiol Sport Promot 2018; 23:71-82 .

    • Search Google Scholar
    • Export Citation
  • 9.

    Milano G , Grasso A & Russo A et al. Analysis of risk factors for glenoid bone defect in anterior shoulder instability. Am J Sports Med 2011; 39:1870-1876 .

    • Search Google Scholar
    • Export Citation
  • 10.

    Thangarajah T , Lambert SM . Management of recurrent shoulder instability in patients with epilepsy. J Shoulder Elbow Surg 2016; 25:1376-1384 .

    • Search Google Scholar
    • Export Citation
  • 11.

    Bushnell BD , Creighton RA , Herring MM . The bony apprehension test for instability of the shoulder: a prospective pilot analysis. Arthroscopy 2008; 24:974-982 .

    • Search Google Scholar
    • Export Citation
  • 12.

    Provencher MT , Frank RM & Leclere LE et al. The Hill-Sachs lesion: diagnosis, classification, and management. J Am Acad Orthop Surg 2012; 20:242-252 .

    • Search Google Scholar
    • Export Citation
  • 13.

    Malgaigne J . Traité des fractures et des luxations. Paris: JB Baillière; 1855 .

  • 14.

    Hill HA , Sachs MD . The grooved defect of the humeral head. Radiology 1940; 35:690-700 .

  • 15.

    Rokous JR , Feagin JA , Abbott HG . Modified axillary roentgenogram. A useful adjunct in the diagnosis of recurrent instability of the shoulder. Clin Orthop Relat Res 1972; 82:84-86 .

    • Search Google Scholar
    • Export Citation
  • 16.

    Bernageau J , Patte D , Debeyre J , Ferrane J . Value of the glenoid profil in recurrent luxations of the shoulder. Rev Chir Orthop Repar Appar Mot 1976; 62(suppl):142-147 .

    • Search Google Scholar
    • Export Citation
  • 17.

    Rozing PM , de Bakker HM , Obermann WR . Radiographic views in recurrent anterior shoulder dislocation. Comparison of six methods for identification of typical lesions. Acta Orthop Scand 1986; 57:328-330 .

    • Search Google Scholar
    • Export Citation
  • 18.

    Itoi E , Lee SB , Amrami KK , Wenger DE , An KN . Quantitative assessment of classic anteroinferior bony Bankart lesions by radiography and computed tomography. Am J Sports Med 2003; 31:112-118 .

    • Search Google Scholar
    • Export Citation
  • 19.

    Rouleau DM , Hébert-Davies J , Djahangiri A , Godbout V , Pelet S , Balg F . Validation of the instability shoulder index score in a multicenter reliability study in 114 consecutive cases. Am J Sports Med 2013; 41:278-282 .

    • Search Google Scholar
    • Export Citation
  • 20.

    Charousset C , Beauthier V , Bellaïche L , Guillin R , Brassart N , Thomazeau H ; French Arthroscopy Society. Can we improve radiological analysis of osseous lesions in chronic anterior shoulder instability? Orthop Traumatol Surg Res 2010; 96(suppl):S88-S93 .

    • Search Google Scholar
    • Export Citation
  • 21.

    Jankauskas L , Rüdiger HA , Pfirrmann CWA , Jost B , Gerber C . Loss of the sclerotic line of the glenoid on anteroposterior radiographs of the shoulder: a diagnostic sign for an osseous defect of the anterior glenoid rim. J Shoulder Elbow Surg 2010; 19:151-156 .

    • Search Google Scholar
    • Export Citation
  • 22.

    Bouliane MJ , Chan H & Kemp K et al. The intra- and inter-rater reliability of plain radiographs for Hill-Sachs and bony glenoid lesions: evaluation of the radiographic portion of the instability severity index score. Shoulder Elbow 2013; 5:33-38 .

    • Search Google Scholar
    • Export Citation
  • 23.

    Edwards TB , Boulahia A , Walch G . Radiographic analysis of bone defects in chronic anterior shoulder instability. Arthroscopy 2003; 19:732-739 .

    • Search Google Scholar
    • Export Citation
  • 24.

    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; 66:159-168 .

    • Search Google Scholar
    • Export Citation
  • 25.

    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; 98:514-519 .

    • Search Google Scholar
    • Export Citation
  • 26.

    Lansdown DA , Dawe R , Cvetanovich GL , Verma NN , Cole BJ & Bach BR et al. Automated 3D MRI allows for accurate evaluation of glenoid bone loss as compared to 3D CT. Arthroscopy 2019 Mar;35:734-740 .

    • Search Google Scholar
    • Export Citation
  • 27.

    Sodickson A , Baeyens PF & Andriole KP et al. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults. Radiology 2009; 251:175-184 .

    • Search Google Scholar
    • Export Citation
  • 28.

    Bishop JY , Jones GL , Rerko MA , Donaldson C ; MOON Shoulder Group. 3-D CT is the most reliable imaging modality when quantifying glenoid bone loss. Clin Orthop Relat Res 2013; 471:1251-1256 .

    • Search Google Scholar
    • Export Citation
  • 29.

    Kubicka AM , Stefaniak J & Lubiatowski P et al. Reliability of measurements performed on two dimensional and three dimensional computed tomography in glenoid assessment for instability. Int Orthop 2016; 40:2581-2588 .

    • Search Google Scholar
    • Export Citation
  • 30.

    Stefaniak J , Kubicka AM , Wawrzyniak A , Romanowski L , Lubiatowski P . Reliability of humeral head measurements performed using two- and three-dimensional computed tomography in patients with shoulder instability. Int Orthop 2020 Jul 26. doi: [Epub ahead of print].

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31.

    Diederichs G , Seim H & Meyer H et al. CT-based patient-specific modeling of glenoid rim defects: a feasibility study. AJR Am J Roentgenol 2008; 191:1406-1411 .

    • Search Google Scholar
    • Export Citation
  • 32.

    Chuang TY , Adams CR , Burkhart SS . Use of preoperative three-dimensional computed tomography to quantify glenoid bone loss in shoulder instability. Arthroscopy 2008; 24:376-382 .

    • Search Google Scholar
    • Export Citation
  • 33.

    Saito H , Itoi E , Sugaya H , Minagawa H , Yamamoto N , Tuoheti Y . Location of the glenoid defect in shoulders. Am J Sports Med 2005; 33:889-93.

    • Search Google Scholar
    • Export Citation
  • 34.

    Saintmard B , Lecouvet F , Rubini A , Dubuc J-E . Is the bare spot a valid landmark for glenoid evaluation in arthroscopic Bankart surgery? Acta Orthop Belg 2009; 75:736-742 .

    • Search Google Scholar
    • Export Citation
  • 35.

    Aigner F , Longato S , Fritsch H , Kralinger F . Anatomical considerations regarding the ‘bare spot’ of the glenoid cavity. Surg Radiol Anat 2004; 26:308-311 .

    • Search Google Scholar
    • Export Citation
  • 36.

    Huysmans PE , Haen PS , Kidd M , Dhert WJ , Willems JW . The shape of the inferior part of the glenoid: a cadaveric study. J Shoulder Elbow Surg 2006; 15:759-763 .

    • Search Google Scholar
    • Export Citation
  • 37.

    Sugaya H , Moriishi J , Kanisawa I , Tsuchiya A . Arthroscopic osseous Bankart repair for chronic recurrent traumatic anterior glenohumeral instability. J Bone Jt Surg - Ser A 2005; 87:1752–60.

    • Search Google Scholar
    • Export Citation
  • 38.

    Baudi P , Righi P & Bolognesi D et al. How to identify and calculate glenoid bone deficit. Chir Organi Mov 2005; 90:145-152 .

  • 39.

    Magarelli N , Milano G , Sergio P , Santagada DA , Fabbriciani C , Bonomo L . Intra-observer and interobserver reliability of the ‘Pico’ computed tomography method for quantification of glenoid bone defect in anterior shoulder instability. Skeletal Radiol 2009; 38:1071-1075 .

    • Search Google Scholar
    • Export Citation
  • 40.

    Gerber C , Nyffeler RW . Classification of glenohumeral joint instability. Clin Orthop Relat Res 2002; 400:65-76 .

  • 41.

    Maqdes A , Chammai Y & Lengert R et al. The intra- and inter-observer reliability of the CT-scan based X index to quantify glenoid bone loss in chronic anterior shoulder instability and its impact on decision making. Eur J Orthop Surg Traumatol 2015; 25:699-703 .

    • Search Google Scholar
    • Export Citation
  • 42.

    Griffith JF , Antonio GE , Tong CWC , Ming CK . Anterior shoulder dislocation: quantification of glenoid bone loss with CT. AJR Am J Roentgenol 2003; 180:1423-1430 .

    • Search Google Scholar
    • Export Citation
  • 43.

    Griffith JF , Yung PSH , Antonio GE , Tsang PH , Ahuja AT , Chan KM . CT compared with arthroscopy in quantifying glenoid bone loss. AJR Am J Roentgenol 2007; 189:1490-1493 .

    • Search Google Scholar
    • Export Citation
  • 44.

    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; 37:731-736 .

    • Search Google Scholar
    • Export Citation
  • 45.

    Saito H , Itoi E , Minagawa H , Yamamoto N , Tuoheti Y , Seki N . Location of the Hill-Sachs lesion in shoulders with recurrent anterior dislocation. Arch Orthop Trauma Surg 2009; 129:1327-1334 .

    • Search Google Scholar
    • Export Citation
  • 46.

    Kodali P , Jones MH , Polster J , Miniaci A , Fening SD . Accuracy of measurement of Hill-Sachs lesions with computed tomography. J Shoulder Elbow Surg 2011; 20:1328-1334 .

    • Search Google Scholar
    • Export Citation
  • 47.

    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; 39:2389-2395 .

    • Search Google Scholar
    • Export Citation
  • 48.

    Kurokawa D , Yamamoto N & Nagamoto H et al. The prevalence of a large Hill-Sachs lesion that needs to be treated. J Shoulder Elbow Surg 2013; 22:1285-1289 .

    • Search Google Scholar
    • Export Citation
  • 49.

    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 glenoid track. J Shoulder Elbow Surg 2007; 16:649-656 .

    • Search Google Scholar
    • Export Citation
  • 50.

    Omori Y , Yamamoto N & Koishi H et al. Measurement of the glenoid track in vivo as investigated by 3-dimensional motion analysis using open MRI. Am J Sports Med.2014; 42:1290-1295 .

    • Search Google Scholar
    • Export Citation
  • 51.

    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; 30:90-98 .

    • Search Google Scholar
    • Export Citation
  • 52.

    Yamamoto N , Shinagawa K , Hatta T , Itoi E . Peripheral-track and central-track Hill-Sachs lesions: a new concept of assessing an on-track lesion. Am J Sports Med 2020; 48:33-38 .

    • Search Google Scholar
    • Export Citation
  • 53.

    Schneider AK , Hoy GA & Ek ET et al. Interobserver and intraobserver variability of glenoid track measurements. J Shoulder Elbow Surg 2017; 26:573-579 .

    • Search Google Scholar
    • Export Citation
  • 54.

    Stefaniak J , Olmos M , Johanston T , Boileau P . Arthroscopic Bankart repair: is on-track/off-track concept enough to predict failures? Shoulder Concepts 2020. Nice Shoul. in press.

    • Search Google Scholar
    • Export Citation
  • 55.

    Di Giacomo G , Peebles LA & Pugliese M et al. Glenoid track instability management score: radiographic modification of the Instability Severity Index Score. Arthroscopy 2020; 36:56-67 .

    • Search Google Scholar
    • Export Citation
  • 56.

    Ajuied A , McGarvey CP , Harb Z , Smith CC , Houghton RP , Corbett SA . Diagnosis of glenoid labral tears using 3-tesla MRI vs. 3-tesla MRA: a systematic review and meta-analysis. Arch Orthop Trauma Surg 2018; 138:699-709 .

    • Search Google Scholar
    • Export Citation
  • 57.

    Friedman LGM , Ulloa SA , Braun DT , Saad HA , Jones MH , Miniaci AA . Glenoid bone loss measurement in recurrent shoulder dislocation: assessment of measurement agreement between CT and MRI. Orthop J Sports Med 2014; 2:2325967114549541 .

    • Search Google Scholar
    • Export Citation
  • 58.

    Stillwater L , Koenig J , Maycher B , Davidson M . 3D-MR vs. 3D-CT of the shoulder in patients with glenohumeral instability. Skeletal Radiol 2017; 46:325-331 .

    • Search Google Scholar
    • Export Citation
  • 59.

    Yanke AB , Shin JJ & Pearson I et al. Three-dimensional magnetic resonance imaging quantification of glenoid bone loss is equivalent to 3-dimensional computed tomography quantification: cadaveric study. Arthroscopy 2017; 33:709-715 .

    • Search Google Scholar
    • Export Citation
  • 60.

    Fernandes de Mello RA , Ma Y & Ashir A et al. 3D Zero Echo Time (ZTE) MRI versus 3D CT for glenoid bone assessment. Arthroscopy 2020; 36:2391-2400 .

    • Search Google Scholar
    • Export Citation
  • 61.

    Breighner RE , Endo Y , Konin GP , Gulotta LV , Koff MF , Potter HG . Technical developments: Zero Echo Time imaging of the shoulder: enhanced osseous detail by using MR imaging. Radiology 2018; 286:960-966 .

    • Search Google Scholar
    • Export Citation
  • 62.

    Metzger PD , Barlow B , Leonardelli D , Peace W , Solomon DJ , Provencher MT . Clinical application of the “glenoid track” concept for defining humeral head engagement in anterior shoulder instability: A preliminary report. Orthop J Sports Med 2013; 1(2):2325967113496213 .

    • Search Google Scholar
    • Export Citation
  • 63.

    Gyftopoulos S , Yemin A & Mulholland T et al. 3DMR osseous reconstructions of the shoulder using a gradient-echo based two-point Dixon reconstruction: a feasibility study. Skeletal Radiol 2013; 42:347-352 .

    • Search Google Scholar
    • Export Citation