Original Research
Musculoskeletal Imaging
May 2008

Prevalence, Pattern, and Spectrum of Glenoid Bone Loss in Anterior Shoulder Dislocation: CT Analysis of 218 Patients

Abstract

OBJECTIVE. The purpose of our study was to determine the prevalence, pattern, and spectrum of glenoid bone loss in anterior shoulder dislocation, to relate this to the frequency of dislocation, and to test the appropriateness of the measurement method.
SUBJECTS AND METHODS. Two hundred eighteen patients with single or recurrent anterior shoulder dislocation underwent shoulder CT examination. Fifteen patients had bilateral dislocation. Prevalence and severity of glenoid bone loss and glenoid fracture were assessed. CT examinations of 56 control subjects without shoulder dislocation were evaluated for glenoid contour and side-to-side variation in glenoid width.
RESULTS. Glenoid bone loss was present in 27 (41%) of 66 patients with first-time unilateral dislocation and 118 (86%) of 137 patients with recurrent unilateral dislocation. Glenoid bone loss ranged from –0.3% to –33% (mean, –10.8% ± 7.9%). Seventy-four (51%) of 145 patients had ≤ 10% glenoid bone loss, 54 (37%) had between 10% and 20%, eight (6%) had between 20% and 25% glenoid bone loss, and nine (6%) had ≥ 25% glenoid bone loss. Glenoid rim fractures were present in 49 (21%) of 233 dislocated shoulders. The number of dislocations correlated moderately with the severity of glenoid bone loss (r = 0.56). The normal side-to-side glenoid width variation was small (0.46 ± 0.81 mm).
CONCLUSION. Glenoid bone loss is common in anterior shoulder dislocation. It is probably multifactorial in origin, is usually mild in degree, and has a maximum observed severity of –33%. Dislocation frequency cannot accurately predict the degree of bone loss.

Introduction

Anterior shoulder dislocation leads to bone loss on the anterior aspect of the glenoid and compression fracture of the posterosuperior aspect of the humeral head (Hill-Sachs deformity) [16]. Glenoid bone loss decreases the glenohumeral contact area. A reduced glenohumeral contact area may increase joint instability and the likelihood of further dislocation. Recently, bone augmentation procedures have been advocated for patients with advanced glenoid bone loss because capsulolabral repair alone may not be sufficient to prevent further dislocation [79]. Although Hill-Sachs deformity is thought to result from impaction of the dislocated humerus against the glenoid, the mechanism of glenoid bone loss has not been investigated; it may potentially arise from either glenoid rim fracture, glenoid rim attrition, or impaction fracture by the dislocated humeral head. Overall, approximately 70% of patients with first-time dislocations can expect dislocation again within 2 years, although this is very much age-related, with further dislocation occurring in 80% of those younger than 20 years, 60% of those 20–40 years old, and fewer than 15% in those older than 40 years [10].
Glenoid and humeral bone loss can be evaluated by radiography and CT [2, 5, 6, 11, 12]. CT examination shows that glenoid bone loss leads to straightening of the normally curved anterior glenoid rim (i.e., an anterior straight line) and reduction in glenoid width of the dislocated side compared with the contralateral, nondislocated side [5, 12]. These features may be evaluated on a CT image obtained en face to the glenoid articular surface [5, 12]. This CT quantification method rests on the observation that normal side-to-side variation in glenoid width is small [5]. CT has high sensitivity (93%) and specificity (78%) for detecting glenoid bone loss and has good agreement (r = 0.79) with shoulder arthroscopy regarding the severity of glenoid bone loss [12].
Because methods of quantifying glenoid bone loss have only recently been described, the prevalence, spectrum, and pattern of glenoid bone loss in a large number of patients with anterior shoulder dislocation are not known. This information is central to the detection and interpretation of bone defects on cross-sectional imaging and to understanding the pathophysiology and consequences of recurrent dislocation.
The primary aim of this study was to prospectively study a large cohort of patients with anterior shoulder dislocation to establish the prevalence, spectrum, and severity of glenoid bone loss. Secondary aims were to investigate the etiology of glenoid bone loss and to test the reliability of the CT technique used.

Subjects and Methods

Patients with Shoulder Dislocation

Clinical details and CT examinations performed in 218 patients referred to the orthopedic department for investigation of anterior shoulder dislocation over a 6-year period between January 2001 and December 2006 were recorded and analyzed. The institutional ethics committee approved the study, for which all patients provided informed consent. Clinical details recorded were patient age and sex as well as side and frequency of shoulder dislocation. Inclusion criteria necessitated that patients have at least one radiographically documented anterior shoulder dislocation. Patients consisted of 171 males and 47 females (mean age, 31 years; range, 12–82 years). Two hundred three (93%) of the 218 patients had unilateral dislocation (141 right side, 62 left side) and 15 (7%) patients had bilateral dislocation. No patients with a prior bone augmenta tion procedure were included.
Fig. 1A Mild glenoid bone loss. Reformatted CT image of affected side en face to glenoid articular surface in 41-year-old man with six dislocations. Note anterior straight line (19.7 mm) (arrowheads). Maximum width of inferior glenoid at right angles to long axis is 28.3 mm.
Fig. 1B Mild glenoid bone loss. Normal contralateral glenoid for comparison. Maximum width of inferior glenoid at right angles to long axis is 31.2 mm, indicating mild (2.9 mm or 9.3%) glenoid bone loss on affected side.
Therefore, the study cohort comprised 233 dislocated shoulders. Of these, 70 (30%) had a single dislocation and 163 (70%) had a recurrent dislocation. This greater preponderance of recurrent dislocations reflects patient recruitment from those referred to the orthopedic department. The number of recurrent dislocations ranged from two to 50 dislocations (mean, 5.4 ± 6.4) (excluding one patient who claimed to have more than 2,000 dislocations). Because both shoulders were examined by CT, the contralateral shoulder was available for reference in all patients.

Subjects Without Shoulder Dislocation

Fifty-six control subjects (24 males, 32 females; mean age, 45 years; range, 14–76 years) with no history of shoulder dislocation, who had undergone high-resolution CT of the upper thorax and both shoulder girdles in an identical manner to the patient group (i.e., with the arms positioned by the chest wall), were evaluated as a reference for normal glenohumeral morphology and side-to-side variation in glenoid width and length. Only patients with disease not likely to affect the size or shape of the glenoid fossa or proximal humerus were defined as healthy subjects. The indication for CT examination in these 56 subjects was sternomanubrial disease in 38 (68%) subjects, clavicle or proximal humeral fractures in 11 (20%), and upper thoracic or proximal humeral tumors in seven (12%). Informed consent was not required by the ethics committee for review of these control CT examinations.

CT Examination Technique and Analysis

Simultaneous CT examination of both shoulders was undertaken in both patients and healthy subjects with either a single-detector helical CT scanner (HiSpeed Advantage, GE Healthcare) using 1-mm acquisitions with 200 mA, 120 kV, and a pitch of 1:1) (n = 118 examinations) or an MDCT scanner (LightSpeed 16 Plus, GE Healthcare) using 16 × 0.625 mm acquisitions with 400 mA, 120 kV, and a pitch of 1:1.75 (n = 100 examinations). The scanning plane extended from the acromion to just below the glenoid, with the patient's arms positioned by the chest wall and the palms pronated. Double oblique reconstruction of each glenoid was used to obtain oblique sagittal images en face to the glenoid articular surface (Advantage Windows, version 4.2, GE Healthcare) (Figs. 1A, 1B, 2A, 2B, 3A, 3B, 4).
On these images, three measurements were obtained. First, the length of the long axis of the glenoid was measured from the level of the supra glenoid tubercle to the inferior margin of the glenoid. Second, the width of the inferior glenoid was measured at right angles to the long axis through the mid portion of the inferior glenoid (Figs. 1A, 1B, 2A, 2B, 3A, 3B, 4). This inferior glenoid refers to the widened inferior half of the glenoid surface (Figs. 1A, 1B, 2A, 2B, 3A, 3B, 4). This in most cases amounted to the maximum width of the glenoid, except in patients with an anterior concavity and in some of those patients with an attached fracture. Third, if present, the length of the anterior straight line along the anterior glenoid contour (Figs. 1A, 2A, 3A, and 4) was measured, and any inward concavity of this contour was noted (Fig. 3A, 3B). If the anterior margin of the glenoid was concave, this was also counted as an anterior straight line. A single investigator with 19 years of working experience with CT performed all CT recon structions and measurements unblinded to clini cal information. Reconstruction, analysis, and filming of each CT data set took less than 10 minutes to complete.
Fig. 2A Moderate glenoid bone loss in 19-year-old man with nine dislocations. Reformatted CT image of affected side en face to glenoid articular surface. Note anterior straight line (23.8 mm) (arrowheads). Maximum width of inferior glenoid at right angles to long axis is 23.2 mm.
Fig. 2B Moderate glenoid bone loss in 19-year-old man with nine dislocations. Normal contralateral glenoid for comparison. Maximum width of inferior glenoid at right angles to long axis is 26.3 mm, indicating moderate (3.1 mm or 11.8%) glenoid bone loss on affected side.
Fig. 3A Severe glenoid bone loss in 43-year-old man with six dislocations. Reformatted CT image of affected side en face to glenoid articular surface shows anterior concavity (arrowheads). Maximum width of inferior glenoid at right angles to long axis is 21.6 mm. Note detached fracture (arrow).
Fig. 3B Severe glenoid bone loss in 43-year-old man with six dislocations. Normal contralateral glenoid for comparison. Maximum width of inferior glenoid at right angles to long axis is 31.2 mm, indicating severe (9.6 mm or 27.5%) glenoid bone loss on affected side.

Presence and Quantification of Glenoid Bone Loss

Glenoid bone loss in patients with unilateral dis location was diagnosed only after two criteria were met. First, an anterior straight line to the glen oid rim had to be present; and second, there had to be a reduced glenoid width in the dislocated shoulder compared with the normal side. In other words, an anterior straight line or reduction in glenoid width in isolation was not sufficient to constitute glenoid bone loss. Both measures were combined because an anterior straight line adds specificity to an isolated measurement of reduced glenoid width [12]. Percentage of glenoid bone loss was measured by dividing the difference in glenoid width between the affected and unaffected sides by the glenoid width of the unaffected side (Figs. 1A, 1B, 2A, 2B, 3A, 3B). No quan titative measure of glenoid bone loss was possible in patients with bilateral dislocation because there was no normal glenoid for comparison.

Presence and Type of Glenoid Rim Fracture

The presence and pattern of glenoid rim fracture were determined on axial and reformatted images through the glenoid (Figs. 4 and 5A, 5B, 5C, 5D, 5E). Glenoid rim fractures were diagnosed by observing either a free bone fragment adjacent to the glenoid rim (a detached fracture) or a focal deformity of the glenoid contour consistent with either a partially detached fracture or a reattached fracture (attached fracture) (Figs. 3A, 3B and 4).

Presence and Quantification of Hill-Sachs Deformity

The presence and pattern of Hill-Sachs de formity were determined on axial and reform atted images through the proximal humerus. Hill-Sachs deformity was graded as being absent or, if present, as minimal, mild, moderate, or severe in degree according to the overall size of the defect on serial images (Fig. 5A, 5B, 5C, 5D, 5E).

Reliability of CT Measurements

Inter- and intraobserver agreement was established on 40 CT examinations (80 shoulders) comprising both healthy individuals and patients with dislocation. For interobserver agreement, two investigators, one with 19 and one with 2 years of working CT experience, independently recon structed and measured the glenoid length and width on 40 CT data sets. For intraobserver agreement, the same 40 CT data sets were recon structed and remeasured, and these second blinded readings were compared with the initial readings. The interval between initial and second CT measurements for interreader reliability was 3–4 weeks.

Data Analysis

SPSS for Windows, version 11.5 (SPSS), was used for statistical analyses. Variables were expressed as mean ± 2 SDs unless otherwise stated. Pearson's chi-square test was used to test for side-to-side or sex differences in normal glenoid width and for length as well as prevalence of glenoid bone loss, Hill-Sachs deformity, and fracture in patients with single or recurrent dislocation. Spearman's cor relation was used to examine the relationship between glenoid bone loss, Hill-Sachs deformity, and number of dis locations. CART (classification and regression tree), a binary tree-structured stati stical method that can help search for hidden structure in data, was applied to help determine a critical level of glenoid bone loss—that is, the level beyond which the patient was more likely to develop increased frequency of dislocation. Intraclass cor relation coefficient was used to assess interreader and intrareader reliability. Intraclass correlation coef ficients were expressed as means (± 95% CIs). A 5% significance level was applied for all tests (p < 0.05).
Fig. 4 Reformatted CT image en face to glenoid articular surface in 15-year-old boy with six dislocations and moderate glenoid bone loss. Note anterior straight line (17.7 mm) (arrowheads). Contour deformity of inferoanterior aspect of glenoid is present (arrow), consistent with reattached fracture. Maximum width of inferior glenoid at right angles to long axis is 22.1 mm (compared with 26.4 mm on unaffected side (not shown), indicating moderate 4.3 mm or 16.3% glenoid bone loss).

Results

Patients with Shoulder Dislocation

Prevalence, pattern, and spectrum of glenoid bone loss—The prevalence of glenoid bone loss in shoulders with single and recurrent unilateral dislocation is shown in Table 1. Glenoid bone loss was present in 145 (71%) of 203 patients (Table 1), being present in 27 of 66 (41%) single and 118 (86%) of 137 recurrent shoulders with dislocation (Table 1). The overall mean percentage of reduction in glenoid width compared with the normal side was –10.8% ± 7.9% (mean ± 1 SD) (range, –0.3% to –33%) (Fig. 6). Absolute reduction in glenoid width was –3.03 ± 2.3 mm (range, –0.1 to –10.1 mm). Glenoid bone loss was more common (p = 0.001) (Table 1) and also more severe (p = 0.001) in recurrent than in single dislocations (Fig. 7). The number of dislocations correlated moderately with increasing severity of glenoid bone loss (r = 0.56). The relationship between number of dislocations and severity of glenoid bone loss is shown in Figure 8. Note how some patients with only one or a few dislocations had severe bone loss, whereas other patients with frequent dislocations had mild bone loss (Fig. 8).
TABLE 1: Prevalence of Glenoid Bone Loss, Glenoid Rim Fracture, an Anterior Straight Line, and Hill-Sachs Deformity in Single and Recurrent Anterior Dislocations
Prevalence
CT FeatureSingle Dislocation (n = 70)Recurrent Dislocation (n = 163)Single and Recurrent Dislocations (n = 233)
Glenoid bone lossa27 (41)a118 (86)a145 (71)a
Glenoid rim fracture11 (16)38 (23)49 (21)
    Detached7 (11)16 (10)23 (10)
    Attached4 (5)22 (13)26 (11)
Anterior straight line34 (49)148 (91)182 (78)
Hill-Sachs deformity57 (81)143 (87)200 (86)
Both anterior straight line and Hill-Sachs deformity
31 (44)
130 (79)
161 (69)
Note—Data are numbers (%) of patients. Glenoid bone loss is defined as anterior straight line occurring in conjunction with relative reduction in glenoid width.
a
Because glenoid bone loss could only be quantified in patients with unilateral dislocation, 203 patients (comprising 66 patients with single dislocation and 137 patients with recurrent dislocation) were used for analysis of glenoid bone loss.
Seventy-four (51%) of the 145 patients with glenoid bone loss incurred ≤ 10% glenoid bone loss, 54 (37%) incurred > 10% but < 20%, and eight (6%) incurred > 20% but < 25% glenoid bone loss (Fig. 7). Nine (6%) patients incurred > 25% glenoid bone loss (Figs. 3A, 3B and 6). CART analysis indicated a critical level of glenoid bone loss to be 13.4%. Below this level, the average number of dislocations was 6.3, whereas above this level the average number of dislocations rose to 10.1. The greatest bone loss seen in this cohort was –33% (Figs. 6 and 8).
Increased length of the anterior straight line correlated positively with a reduction in glenoid width (r = 0.72), indicating that as glenoid width diminished, the normally curved anterior edge of the glenoid became progressively straighter (Figs. 1A, 1B, 2A, 2B, 3A, 3B). With severe bone loss, an anterior concavity to the anterior glenoid was observed (Fig. 3A, 3B). Such anterior concavity was present in 23 (10%) of 233 dislocated shoulders. If an anterior concavity is present, glenoid bone loss is generally severe (22.8 ± 7.4%).
Glenoid rim fracture was present in 49 (21%) of 233 dislocated shoulders (Table 1). The relative prevalence of detached or attached glenoid rim fracture is shown in Table 1. Glenoid rim fracture was more common in recurrent than single dislocation, although this difference was not significant (p = 0.39) (Table 1).
Prevalence of Hill-Sachs deformity—Hill-Sachs deformity was present in 200 (86%) of 233 dislocated shoulders (Table 1). Hill-Sachs deformity was not more common (p = 0.21) (Table 1) but was more severe (p = 0.008) in recurrent than in single dislocations. A weak positive correlation was seen between glenoid bone loss and increasing severity of Hill-Sachs deformity (r = 0.24, p = 0.03).
Fig. 5A Assessing severity of Hill-Sachs deformity. Axial images of proximal humerus show examples of normal smooth rounder humeral contour (A) and minimal (arrow, B), mild (arrow, C), moderate (arrow, D), and severe (arrow, E) degrees of Hill-Sachs deformity. Although one image is presented for each grade, severity of Hill-Sachs deformity is assessed on serial images rather than on a single image.
Fig. 5B Assessing severity of Hill-Sachs deformity. Axial images of proximal humerus show examples of normal smooth rounder humeral contour (A) and minimal (arrow, B), mild (arrow, C), moderate (arrow, D), and severe (arrow, E) degrees of Hill-Sachs deformity. Although one image is presented for each grade, severity of Hill-Sachs deformity is assessed on serial images rather than on a single image.
Fig. 5C Assessing severity of Hill-Sachs deformity. Axial images of proximal humerus show examples of normal smooth rounder humeral contour (A) and minimal (arrow, B), mild (arrow, C), moderate (arrow, D), and severe (arrow, E) degrees of Hill-Sachs deformity. Although one image is presented for each grade, severity of Hill-Sachs deformity is assessed on serial images rather than on a single image.
Fig. 5D Assessing severity of Hill-Sachs deformity. Axial images of proximal humerus show examples of normal smooth rounder humeral contour (A) and minimal (arrow, B), mild (arrow, C), moderate (arrow, D), and severe (arrow, E) degrees of Hill-Sachs deformity. Although one image is presented for each grade, severity of Hill-Sachs deformity is assessed on serial images rather than on a single image.
Fig. 5E Assessing severity of Hill-Sachs deformity. Axial images of proximal humerus show examples of normal smooth rounder humeral contour (A) and minimal (arrow, B), mild (arrow, C), moderate (arrow, D), and severe (arrow, E) degrees of Hill-Sachs deformity. Although one image is presented for each grade, severity of Hill-Sachs deformity is assessed on serial images rather than on a single image.
Anterior straight line and Hill-Sachs deformity—An anterior straight line was observed less frequently than Hill-Sachs deformity in single dislocation (p < 0.001) and more frequently than Hill-Sachs deformity in recurrent dislocation (Table 1), although this difference was not significant (p = 0.12). Either a humeral (Hill-Sachs deformity) or glenoid (anterior straight line) bone defect was evident in all shoulders with recurrent dislocation.

Subjects Without Shoulder Dislocation

Glenoid width, length, and side-to-side variation in normal shoulders without dislocation—In the 56 subjects without dislocation (i.e., 112 normal shoulders), the normal glenoid fossa width was found to be 26.5 ± 4.6 mm and the glenoid fossa length, 40.1 ± 7.6 mm. Side-to-side variation in glenoid width was 0.46 ± 0.81 mm. Side-to-side variation in glenoid length was 0.78 ± 0.68 mm. Both glenoid width and length were significantly larger in males than females (p < 0.0001). For each sex, no significant side-to-side difference in either glenoid width (males, p = 0.25; females, p = 0.28) or length (males, p = 0.53; females, p = 0.78) was found.
Prevalence and pattern of anterior straight line and Hill-Sachs-type deformity in normal shoulders without dislocation—An anterior straight line to the glenoid rim was present in seven (2%) of 282 nondislocated shoulders (comprising 112 shoulders in healthy subjects without dislocation and 170 nonaffected shoulders in patients with unilateral dislocation). This anterior straight line measured 5.6–11.9 mm (mean, 7.9 mm). A Hill-Sachs-type deformity was present in two (0.7%) of 282 nondislocated shoulders. This Hill-Sachs-type deformity was classified as mild in both cases.

Inter- and Intraobserver Reliability of CT Measurements

Interobserver agreement, as determined by the intraclass correlation coefficient, was 0.914 for glenoid width and 0.858 for glen oid length measurements. The intraobserver measurement difference was –0.24 ± 2.27 mm (mean ± 2 SDs) for glenoid width and 0.09 ± 3.27 mm for glenoid length. Intraobserver agreement was 0.958 for glenoid width and 0.790 for glenoid length measurements. The interobserver measurement difference was –0.14 ± 1.40 mm for glenoid width and 0.22 ± 3.94 mm for glenoid length.

Discussion

Glenoid bone loss occurs primarily on the anterior rather than the anteroinferior aspect of the glenoid [4, 5]. Viewing the glenoid fossa as a clock face, with the superior and inferior aspects represented by 12:00 and 6:00 and the anterior aspect by 3:00, glenoid bone loss occurs between 2:30 and 4:20 [4]. Glenoid bone loss is seen on CT as straightening of the anterior curvature of the glenoid and relative reduction in glenoid width [5]. This is a more reliable measure of glenoid bone loss on CT than cross-sectional area [5]. Compared with arthroscopy, the sensitivity and specificity of CT in detecting glenoid bone loss are 93% and 79% [12]. A high correlation (r = 0.79) also exists between CT and arthroscopy regarding severity of bone loss [12].
This study reveals that glenoid bone loss is common, being evident in 41% of single and 86% of recurrent dislocated shoulders. This is in agreement with the radiographic study of Edwards et al. [6], who undertook a fluoroscopically guided radiographic analysis (“Bernageau profile view”) of 107 recurrent dislocated shoulders. Although no quantitative analysis was undertaken, a glenoid bone defect was present in 75% of cases, including a fracture in 51%; loss of the anterior angle (“cliff sign”) in 16%; and blunting of the anterior angle (“blunted angle sign”) in 33% [6]. Rowe et al. [10], in a surgical study of 162 recurrent dislocations, showed glenoid rim damage in 73% comprising eburnation, erosion, or fracture. Three previous CT-based studies have addressed glenoid bone loss [35]. Griffith et al. [5], in a study of 50 patients, analyzed which methods optimally quantify glenoid bone loss. Sugaya et al. [3] applied a best-fit circle to the inferior glenoid on 3D reconstructed CT images. Glenoid contour deformity was present in 90 (90%) of recurrent dislocated shoulders, comprising a fracture in 50% and a contour deformity in 40%. The size of the bone fragment was used as a quantitative measure of bone loss in patients with fracture, although no quantitative analysis was undertaken in patients without fracture [3]. Saito et al. [4] studied the location of the glenoid defect on CT but did not undertake a quantitative assessment of the defect.
Our study, therefore, is the first large-scale quantitative study of the spectrum of glenoid bone loss occurring in anterior shoulder dislocations. It shows that glenoid bone loss is very common, is usually mild (< 10%) in degree, and has a maximum severity of approximately 33%. Bone loss greater than one third of the normal glenoid width was not observed in any patient. This finding is to be expected because more severe glenoid bone loss would involve erosion of the thicker middle third of the glenoid. More severe degrees of bone loss result in a concavity to the anterior glenoid rim rather than progressive flattening of the anterior glenoid. Only modest correlation was present between frequency of dislocation and severity of glenoid bone loss, indicating that one cannot accurately predict severity of glenoid bone loss on the basis of the number of dislocations alone. Indeed, several of the most severe cases of glenoid bone loss occurred in patients with only one or a few dislocations. The inverse exponential relationship observed between the number of dislocations and the severity of glenoid bone loss is as expected because bone loss will proceed more quickly initially through the thinner, peripheral parts of the glenoid and then more slowly through the thicker, central parts of the glenoid.
This study defines the spectrum of glenoid bone loss, which is the first step to knowing the optimal level of bone loss at which bone augmentation procedures should be considered [8, 9]. In this cross-sectional study using CART regression analysis, we attempted to define a critical level of glenoid bone loss by determining that level above which the patient is more likely to have experienced more frequent dislocations. This critical level was found to be 13.4%. Beyond this level, the num ber of dislocations experienced by the patient rose steeply from six to 10 dislocations. This does not necessarily imply that this is the level at which bone augmentation surgery should be undertaken. That particular level has not yet been determined because it is only recently that means of quantifying glenoid bone loss have been available, and very little data exist on the prevalence and severity of glenoid bone loss. Some orthopedic surgeons have recommended 25%, others 33%, whereas others recommend bone grafting be undertaken if there is a large glenoid defect [8, 11, 1315]. Our study, through defining the spectrum of glenoid bone loss, provides baseline data for defining the optimal level of surgical intervention in the future.
Fig. 6 Histogram shows spectrum of severity of glenoid bone loss in 203 patients with unilateral dislocation. Each bar represents 2.5% increment in glenoid bone loss—that is, 2.5% change in glenoid width. Most severe glenoid bone loss observed was 33%.
Fig. 7 Box-and-whisker plot shows severity of glenoid bone loss for single and recurrent dislocations in 203 patients with unilateral dislocation. Horizontal bar depicts median; box, interquartile range; and whiskers, range. Glenoid bone loss was usually mild but occasionally was severe in single dislocations. Loss was more severe (p = 0.001) and more variable in recurrent dislocations.
Fig. 8 Line graph shows relationship between number of dislocations and percentage of glenoid bone loss in 203 patients with unilateral dislocation. Central line is fitted line mean; upper and lower lines are 95% CIs of fitted line. Note how even severe glenoid bone loss may occur in some patients with only one or a few dislocations.
The frequency of 86% for Hill-Sachs deformity in this CT-based study is comparable to the 76–90% reported from radiographic studies [6, 10, 16]. Hill-Sachs deformity results from impaction of the posterosuperior aspect of the humerus against the glenoid [2, 6]. The origin of glenoid bone loss is less clear. It is not likely to be solely due to fracture because in our study, the prevalence of glenoid rim fracture was only 21%. Similarly, it is unlikely to be the glenoid equivalent of a Hill-Sachs deformity because only a weak association between the severity of Hill-Sachs deformity and glenoid bone loss was found. Nevertheless, it was not rare to find glenoid bone loss of 5–10% in patients with only a single dislocation in the absence of a glenoid rim fracture. Overall, it seems most likely that glenoid bone loss is multifactorial in origin, resulting from glenoid rim erosion or fracture during dislocation and humeral head impaction after dislocation. Some form of bone defect—either Hill-Sachs deformity or an anterior straight line—was present in all patients with recurrent dislocation.
Our study confirms the usefulness of CT in quantifying glenoid bone loss. CT allows both shoulders to be simultaneously examined. As shown, little side-to-side difference in normal glenoid width exists so both glenoids can be readily compared. The examination and analysis are easy to perform and the repeatability of the test is high. The main limitations of CT are that it cannot be used to accurately quantify glenoid bone loss in bilateral dislocations (because there is no normal shoulder for reference), and it involves irradiation of an area close to the thyroid and breast, although this can be minimized by ensuring a scanning plane limited to the glenoid region only.
MRI is the usual method of investigating anterior shoulder dislocation. Although MR images obtained directly en face to the glenoid fossa should be comparable to reconstructed CT images, MRI may not allow quantification of glenoid bone loss because the contralateral glenoid is not included for comparison. However, MRI should allow one to select those patients who would benefit from CT quantification of glenoid bone loss.
Our study has some limitations. First, as in all published studies of this nature, the frequency of dislocation was established retrospectively. As a result, the number of dislocations cited by patients with frequent dislocations may not be entirely accurate. Second, when analyzing CT examinations, observers were not blinded to whether the shoulder had previously dislocated. It is difficult to remove this bias because CT shows contour deformities indicative of dislocation. Third, no arthroscopic quantification of glenoid bone loss was available, although a previous study has shown good correlation between CT and arthroscopy in this respect [12]. Fourth, an ordinal measure of Hill-Sachs deformity was used only after several quantitative methods (e.g., humeral cross-sectional area, maximum dimensions of defect, best circular fit) proved unreliable.
In conclusion, glenoid bone loss is almost as common as Hill-Sachs deformity in anterior shoulder dislocation. Glenoid bone loss is probably multifactorial in origin and is usually mild in degree, with a maximum observed severity of –33%. Occasionally, only a single or a few dislocations may result in a large bone defect. Dislocation frequency cannot accurately predict the degree of bone loss, which helps to justify the use of CT.

Footnotes

Address correspondence to J. F. Griffith ([email protected]).
CME
This article is available for CME credit. See www.arrs.org for more information.

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 1247 - 1254
PubMed: 18430839

History

Submitted: August 9, 2007
Accepted: November 6, 2007

Keywords

  1. CT
  2. dislocation
  3. glenoid
  4. shoulder

Authors

Affiliations

James F. Griffith
Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing St., Shatin, Hong Kong, SAR, China.
Gregory E. Antonio
Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing St., Shatin, Hong Kong, SAR, China.
Patrick S. H. Yung
Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, SAR, China.
Eric M. C. Wong
Centre for Epidemiology and Biostatistics, Postgraduate Education Centre, Faculty of Medicine, Prince of Wales Hospital, Hong Kong, SAR, China.
Alfred B. Yu
Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing St., Shatin, Hong Kong, SAR, China.
Anil T. Ahuja
Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing St., Shatin, Hong Kong, SAR, China.
Kai Ming Chan
Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, SAR, China.

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