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Use of Preoperative Three-Dimensional Computed Tomography to Quantify Glenoid Bone Loss in Shoulder Instability
Use of Preoperative Three-Dimensional Computed Tomography to Quantify Glenoid Bone Loss in Shoulder Instability Tai-Yuan Chuang, M.D., Christopher R. Adams, M.D., and Stephen S. Burkhart, M.D.
Purpose: The purpose of this study was to determine if three-dimensional computed tomography (3-D CT) scans of the glenoid can be used to accurately quantify, by means of a glenoid index, bone loss in patients with anterior glenohumeral instability, and to compare the results with arthroscopic measurements to determine if the 3-D CT scan can preoperatively predict which patients with anterior glenohumeral instability will benefit from a bone grafting procedure. Methods: From 2003 to 2006, 188 patients with anterior glenohumeral instability underwent arthroscopic evaluation and treatment by the senior author (S.S.B.). Of 188 total patients, there were 25 patients ranging in age from 15 to 43 years (median, 19 years) who underwent 3-D CT evaluations of both shoulders followed by arthroscopy of the unstable shoulder. For an arthroscopically measured bone loss of less than 25% of the inferior glenoid diameter, an arthroscopic Bankart repair was performed; for a glenoid bone loss of greater than or equal to 25%, an open Latarjet reconstruction was performed. We defined the glenoid index as the ratio of the maximum inferior diameter of the injured glenoid compared to the maximum inferior diameter of the uninjured contralateral glenoid as calculated from the 3-D CT scans. If the glenoid index was greater than 0.75, the patient was predicted to benefit from an arthroscopic Bankart repair (the need for surgery and the type of surgery having been determined on the basis of arthroscopic measurements). However, if the glenoid index was less than or equal to 0.75, the patient was predicted to benefit from an open Latarjet procedure. The results of each patient’s glenoid index were compared with the arthroscopic decision to perform either an arthroscopic Bankart repair or an open Latarjet procedure. Results: Of the 25 patients included in this study, 13 patients underwent an open Latarjet procedure and 12 patients underwent an arthroscopic Bankart repair. The 3-D CT scans accurately predicted the arthroscopic decisions to perform an arthroscopic Bankart repair or open Latarjet in 24 (96%) of 25 cases (Fisher exact test; P ⬍ .001). Conclusions: The glenoid index as calculated from the 3-D CT scan accurately predicted the requirement of a bone grafting procedure for 24 (96%) of 25 patients when the benchmark value of 0.75 was used. The 3-D CT scan can therefore be used by surgeons as an additional diagnostic tool for preoperative planning and patient counseling. Level of Evidence: Level III, development of diagnostic criteria with universally applied reference (nonconsecutive patients). Key Words: Bankart repair—Bone graft— Computed tomography—Glenoid index—Instability—Shoulder arthroscopy—Shoulder instability.
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e believe that the treatment of anterior glenohumeral instability with significant bone loss requires a bone grafting procedure to prevent the
From The San Antonio Orthopaedic Group, San Antonio, Texas, U.S.A. S.S.B. is a consultant for, and receives royalties from, Arthrex, Inc. The other authors report no conflict of interest. Address correspondence and reprint requests to Stephen S. Burkhart, M.D., 400 Concord Plaza Dr, Ste 300, San Antonio, TX 78216, U.S.A. E-mail: [email protected] © 2008 by the Arthroscopy Association of North America 0749-8063/08/2404-7372$34.00/0 doi:10.1016/j.arthro.2007.10.008
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recurrence of instability or dislocation and ultimately to improve the clinical outcome.1-3 The difficulty lies in determining the amount of bone loss that represents a clinically significant deficit. The arthroscopic appreciation of an inverted pear–shaped glenoid and quantification of the amount of glenoid bone loss using the glenoid bare spot as a reference point have been previously described as accurate and well-accepted guides to determine significant bone loss.3-5 Burkhart and DeBeer3 showed that in patients with anterior glenohumeral instability and an inverted pear– shaped glenoid, which represents a loss of greater than
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 24, No 4 (April), 2008: pp 376-382
PREOPERATIVE 3-D CT TO QUANTIFY GLENOID BONE LOSS 25% of the maximum inferior glenoid width, the recurrence rate of shoulder instability or dislocation after an arthroscopic Bankart repair was 67%. However, patients with less than 25% loss of the maximum inferior glenoid width had a recurrence rate of only 4%. Three-dimensional computed tomography (3-D CT) has been used for measuring bone loss in patients with anterior glenohumeral instability.6 However, to our knowledge, there have been no CT studies in the literature that quantify anterior glenoid bone loss and compare it to the measured bone loss with an arthroscopically validated method. In this study, we used 3-D CT imaging of both the injured and intact shoulders to measure the amount of glenoid bone loss in the injured shoulder. We then compared the CT measurements and CT-derived glenoid index to the direct arthroscopic measurements and arthroscopically derived glenoid index of patients who underwent treatment for anterior glenohumeral instability. If the arthroscopically derived glenoid index was greater then 0.75, then an arthroscopic Bankart repair was done. If the arthroscopically derived glenoid index was less than 0.75, then an open Latarjet procedure with coracoid bone grafting of the glenoid was performed. All surgical treatment decisions were based on the arthroscopic findings and measurements. We compared the CT-derived glenoid index of each patient with the arthroscopically derived glenoid index. We hypothesized that the 3-D CT– derived glenoid index would correlate well with the arthroscopically derived glenoid index and that the CT measurements would therefore be useful in accurately predicting the preferred treatment (arthroscopic Bankart repair v open bone grafting). METHODS The study was done with institutional approval as per the research requirements of The Orthopaedic Institute in San Antonio, Texas. From 2003 to 2006, 188 patients with anterior glenohumeral instability underwent arthroscopic evaluation and treatment by the senior author (S.S.B.). All of these patients had diagnostic arthroscopic evaluations of their shoulders to determine the morphology of their glenoids. Through a standard anterosuperolateral viewing portal the glenoids were viewed en face and classified as either pear-shaped or inverted pear–shaped. Furthermore, the amount of glenoid bone loss was quantified arthroscopically using a validated methodology based on the glenoid bare spot, which is the center of the inferior glenoid circle.4
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Of the 188 patients, there were 25 nonconsecutive patients ranging in age from 15 to 43 years (median, 19 years) who underwent 3-D CT evaluations of both of their shoulders. The scans were done by a General Electric Lightspeed Ultra (Milwaukee, WI) with 8-slice scans converted to 3-D CT reconstructions by combined standard and bone algorithms. Our criteria for obtaining a 3-D CT scan were: (1) at least 3 known shoulder dislocations; (2) total duration of all dislocations more than 4 hours; or (3) suspicion of significant bone loss on plain films or magnetic resonance imaging. A linear method was used to calculate the amount of bone loss of the injured glenoid compared to the uninjured contralateral glenoid with the 3-D CT scans. The first step in the process was obtaining an en face view of the uninjured glenoid with the 3-D CT scan. The most superior aspect of the glenoid is just posterior to the base of the coracoid and is labeled as A1 (Fig 1A). The most inferior aspect of the glenoid is the farthest point from A1 and usually corresponds with the lateral ridge of the scapular body. This point is labeled B1. A line is then drawn connecting A1 to B1 (labeled A1B1 in Fig 1A). The line A1B1 corresponds to the normal glenoid height (H1) of the uninjured shoulder (A1B1 ⫽ H1). The second line drawn (C1D1) is perpendicular to A1B1 and is adjusted up or down until it is at the widest portion of the inferior glenoid (Fig 1B). The line C1D1 corresponds to the normal inferior glenoid width (W1) of the uninjured shoulder (C1D1 ⫽ W1). The intersection of lines A1B1 and C1D1 is labeled O1 (Fig 1C), which represents the geometric center of the inferior glenoid circle (Fig 1D). The line O1D1 corresponds to the radius of the normal inferior glenoid circle (R1) of the uninjured shoulder (O1D1 ⫽ R1). An en face view of the injured glenoid is then obtained. The length of the glenoid is measured in a similar fashion as the uninjured glenoid and line A2B2 (H2) is drawn (Fig 2A). We made the assumption that the injured glenoid with the Bankart lesion had morphology identical to the uninjured glenoid before the injury.6 The radius of the inferior glenoid circle was then calculated through basic proportions. Because R1/H1 ⫽ R2/H2, R2 could be calculated by the following formula: R2 ⫽ (R1/H1)*H2. Therefore, the geometric center of the inferior glenoid circle (O2) could be found a distance equal to R2 from the point B2 (Fig 2B). A new line is drawn that crosses point O2 and is perpendicular to line A2B2. This line is labeled C2D2 (Fig 2C) and represents the inferior width of the
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FIGURE 1. Normal glenoid, left shoulder. (A) The long axis of the glenoid is defined by line A1B1. (B) The widest portion of the inferior glenoid is line C1D1, which is perpendicular to line A1B1. (C) The intersection of lines A1B1 and C1D1 is labeled O1, and it represents the geometric center of the inferior glenoid circle (D).
injured glenoid (W2). A virtual inferior glenoid circle can be drawn on the injured glenoid which clearly shows the amount of anteroinferior glenoid bone loss (Fig 2D). The predicted preinjury width of the injured glenoid (W2=) can then be calculated with the following formula: W2= ⫽ (W1/H1)*H2. This calculation normalizes the preinjury width by accounting for any height difference between the injured and uninjured glenoid. The glenoid index is then calculated as the ratio of the postinjury width of the injured glenoid to the preinjury width of the uninjured glenoid. It was calculated through the following formula: glenoid index ⫽ W2/W2=. Therefore, the 3-D CT scan was used to calculate a glenoid index for each patient. Because it has been determined that patients with bone loss comprising less than 25% of the inferior glenoid diameter do well with an arthroscopic Bankart repair alone, we have used a glenoid index of 0.75 as our threshold for predicting which patients would benefit from a bone grafting procedure.3
If the glenoid index was greater than 0.75, the patient was predicted to do well with an arthroscopic Bankart repair without bone grafting. However, if the glenoid index was less than or equal to 0.75, the patient was predicted to require an open Latarjet procedure in order to restore optimal stability. Each patient’s glenoid index was correlated with the arthroscopic decision to perform either an arthroscopic Bankart repair or an open Latarjet procedure (Tables 1 and 2). Our decision to perform an arthroscopic stabilization versus open bone grafting was based solely on the arthroscopic findings and arthroscopic measurements of bone deficiency. RESULTS Of the 25 patients included in this study, 13 patients underwent an open Latarjet procedure and 12 patients underwent an arthroscopic Bankart repair. Based on the procedural diagnostic benchmark of 0.75 for the glenoid index, 12 (92%) of the 13 patients who un-
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FIGURE 2. Injured glenoid with anteroinferior bone loss, right shoulder. In (A), (B), and (C), lines are drawn as in Figure 1 to represent the height (A2B2) and maximum inferior glenoid width (C2D2). The intersection of these two lines at point O2 defines the geometric center of the inferior glenoid circle before bone loss, so that the amount of bone loss is readily apparent in (D) as the vacant area that is anterior to C2 within the glenoid circle.
derwent an open Latarjet procedure and all 12 of the patients who underwent an arthroscopic Bankart repair were correctly classified, so that a total of 24 (96%) of 25 procedures were accurately predicted TABLE 1.
(Fisher exact test; P ⬍ .001). For the correctly classified cases, the glenoid index ranged from 0.577 to 0.747 (median, 0.668) for open Latarjet procedures and from 0.847 to 0.964 (median, 0.914) for arthro-
Details of the 13 Patients Who Underwent an Open Latarjet Procedure
Case No.
Age (yrs)
H1
W1
R1
H2
R2
W2
W2=
3-D CT Glenoid Index
1 2 3 4 5 6 7 8 9 10 11 12 13
24 21 19 17 21 24 27 41 16 19 24 21 19
3.4 3.7 2.4 3.4 2.7 2.5 2.25 2.2 2.05 6.2 6 5.8 2.5
2.35 2.95 1.8 2.6 2.4 2.1 1.95 1.9 1.5 5 4.4 4 1.8
1.2 1.5 0.9 1.3 1.2 0.9 0.9 1 0.8 2.5 2.3 2.05 0.9
2.9 4.4 2.5 3.4 2.7 3.4 2.6 2.4 1.9 6.3 6.4 9.0 3.2
1.02 1.78 0.94 1.30 1.20 1.22 1.04 1.09 0.74 2.54 2.45 3.18 1.15
1.7 2.4 1.4 1.7 1.6 2 1.3 1.2 1 3.4 3 3.8 1.7
2.00 3.51 1.88 2.60 2.40 2.86 2.25 2.07 1.39 5.08 4.69 6.21 2.30
0.848 0.684 0.747 0.654 0.667 0.700 0.577 0.579 0.719 0.669 0.639 0.612 0.738
NOTE. The units for height (H), width (W), and radius (R) were measured in centimeters (cm). Abbreviation: 3-D CT, three-dimensional computed tomography.
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T-Y. CHUANG ET AL. TABLE 2.
Details of the 12 Patients Who Underwent an Arthroscopic Bankart Repair
Case No.
Age (yrs)
H1
W1
R1
H2
R2
W2
W2=
3-D CT Glenoid Index
1 2 3 4 5 6 7 8 9 10 11 12
43 17 15 19 16 24 26 21 19 16 18 17
2.35 2.1 2.2 2.9 2.5 1.8 2.2 5.3 2.3 8 2.7 2.6
1.6 1.7 1.9 2.2 1.7 1.4 1.55 3.7 1.55 6.1 1.9 2
0.85 0.85 1 1.05 0.9 0.65 0.8 1.9 0.9 3.1 1 1.1
1.9 2.3 2.2 2.8 2.6 1.8 1.95 5.8 2.5 7.1 2.7 2.6
0.69 0.93 1.00 1.01 0.94 0.65 0.71 2.08 0.98 2.75 1.00 1.10
1.2 1.7 1.8 1.8 1.55 1.35 1.2 3.7 1.5 5 1.75 1.7
1.29 1.86 1.90 2.12 1.77 1.40 1.37 4.05 1.68 5.41 1.90 2.00
0.928 0.913 0.947 0.847 0.877 0.964 0.873 0.914 0.890 0.924 0.921 0.850
NOTE. Height (H), width (W), and radius (R) were measured in centimeters.
scopic Bankart repairs. The incorrectly classified open Latarjet procedure had a glenoid index of 0.848. This value was twice as far from the median as any other value for open Latarjet procedures, so the glenoid index for this case was a statistical outlier. This patient has done well with the open Latarjet procedure, and we are confident that our arthroscopic measurement criteria accurately assigned this patient to the open Latarjet group. We believe that in this patient, the CT scan did not accurately show the bone loss because of a technical or artifactual problem with the scan. DISCUSSION Anterior glenohumeral stability is dependent upon balanced soft tissues and a full concentric arc of bony support. After an anterior glenohumeral dislocation, the value of such structures becomes obvious. The importance of balanced soft tissues both anteriorly and posteriorly has been well established in the literature.7,8 The need for a sufficient glenoid base to support a full arc of motion is generally accepted; however, the amount of anterior glenoid bone required to prevent future anterior instability is still being elucidated. One recent study suggested that glenoid bone loss in the 20% to 30% range can be addressed by arthroscopic Bankart repair.9 These authors reported a 13.3% rate of recurrent instability at a mean follow-up of 34 months, while other studies have suggested that a loss of more than 20% to 25% of the inferior glenoid width predisposes a patient to future anterior instability.2,3,10-13 In such cases, a bone grafting procedure may be a necessary adjuvant procedure to increase the glenohumeral stability and prevent future recurrences of anterior subluxations or dislocations.2,3,6,10,14,15
The prevalence of glenoid lesions after an anterior glenohumeral dislocation is quite variable in the literature.6,13,14 The variability may be caused by different patient populations, imaging modalities, and/or the variable expression of glenoid lesions. Sugaya et al.6 evaluated 100 patients with recurrent anterior instability and found that 90% of them had glenoid lesions on 3-D CT scans; however, only 50% of them had osseous fragments while the remaining 40% had changes to the anterior glenoid rim consistent with compression. The CT scan with 3-D reconstructions provides the surgeon with a bony model to evaluate the glenoid rim morphology.6,14,16,17 However, to date there have been no CT studies in the literature that quantify anterior glenoid bone loss and compare it to glenoid bone loss determined by an arthroscopically validated method. Burkhart et al.4 arthroscopically evaluated the glenoid bare spot in 56 patients with no evidence of instability.4 The investigators measured the distance from the bare spot to the anterior, posterior, and inferior glenoid margins. The glenoid bare spot was consistently found to be at the center of a virtual circle of the inferior glenoid. The bare spot was shown to be a consistent, reliable marker that can be used arthroscopically to quantify the amount of anterior glenoid bone loss. A recent study by Kralinger et al.18 suggests that the bare spot of the glenoid might not consistently be located at the center of the inferior glenoid, and therefore might not be a good landmark for calculating glenoid bone loss. However, their cadaveric study was performed on embalmed specimens with an average age of 81.6 years, introducing the possibility of artifactual error from embalming and from the potentially
PREOPERATIVE 3-D CT TO QUANTIFY GLENOID BONE LOSS high anatomic variation related to the extreme age of the specimens.19 In contradistinction, the study by Burkhart et al.20 was performed in young live healthy subjects in which the glenoid bare spot was identified and directly measured arthroscopically. Recognizing this controversy, we believe that the arthroscopic measurements in young live individuals have the least likelihood of introducing artifactual error, and therefore we believe we are justified in basing our treatment decisions on these arthroscopic measurements. The normal appearance of a glenoid is pear-shaped with the inferior portion of the glenoid being wider than the superior portion. After an anterior dislocation, a significant loss of anterior–inferior glenoid bone can result in an inverted pear-shaped glenoid. Lo et al.5 arthroscopically evaluated 53 patients with anterior instability and used the bare spot to determine the amount of inferior glenoid bone loss that is necessary to create an inverted pear-shaped glenoid. Furthermore, 6 fresh-frozen cadaveric specimens were sequentially cut to determine the amount of bone loss required to create an inverted pear-shaped glenoid. The results show that a loss of 25% of the inferior glenoid width arthroscopically or 27% of the inferior glenoid width in the cadaveric glenoids resulted in the appearance of an inverted pear-shaped glenoid. Therefore, a loss of 25% to 27% of the inferior glenoid width results in the appearance of an inverted pear-shaped glenoid. Burkhart and DeBeer3 analyzed the results of 194 consecutive arthroscopic Bankart repairs by a suture anchor technique for traumatic anterior glenohumeral instability. The investigators discovered that if there was no significant glenoid bone loss (pear-shaped glenoid) the recurrence rate for subluxation or dislocation was 4%; however, if there was significant bone loss (inverted pear–shaped glenoid) the recurrence rate was 67%. Their study concluded that patients with significant glenoid bone loss require a bone grafting procedure (e.g., Latarjet procedure) to decrease the rate of recurrent subluxation or dislocation. The authors subsequently changed their approach to patients with anterior glenohumeral instability. In their revised approach, the patients had their inferior glenoid widths measured arthroscopically (based on the glenoid bare spot) at the beginning of every instability case. All patients with glenoid bone loss of 25% or more of the inferior glenoid diameter (glenoid index, ⱕ0.75) were treated with an open Latarjet procedure. In a subsequent study, the authors tested their new clinical approach and found that their patients with a Latarjet procedure had a recurrence rate of only 4.9%.20 This result was far better than their earlier
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arthroscopic Bankart recurrence rate of 67% in patients with a similar degree of glenoid bone deficiency. It is now established that patients without significant glenoid bone loss who undergo an arthroscopic Bankart repair can expect a recurrence rate under 5%.3 Similarly, patients who undergo an open Latarjet procedure for significant glenoid bone loss can also expect a recurrence rate under 5%.20 There were several limitations of our study. Although the arthroscopic glenoid bare spot has been shown by our senior author to be a very reliable marker for the center of the inferior glenoid, it is not known whether the arthroscopic or the 3-D CT scan measurement is the true gold standard. Secondly, we used an en face view with our 3-D CT scan. The acquisition of such a view is operator-dependent. Furthermore, all of our measurements were manual (without the aid of computer software), which could introduce human error.
CONCLUSIONS The glenoid index as calculated from the 3-D CT scan accurately predicted the requirement of a bone grafting procedure for 24 (96%) of 25 patients when the benchmark value of 0.75 was used. The 3-D CT scan can therefore be used by surgeons as an additional diagnostic tool for preoperative planning and patient counseling. Acknowledgment: The authors thank John D. Schoolfield, M.S., for his statistical analysis and assistance with the preparation of the manuscript.
REFERENCES 1. Latarjet M. Techniques in the treatment of recurrent dislocation of the shoulder. Lyon Chir 1965;61:313-318. 2. Bigliani LU, Newton PM, Steinmann SP, Connor PM, Mcllveen SJ. Glenoid rim lesions associated with recurrent anterior dislocation of the shoulder. Am J Sports Med 1998; 26:41-45. 3. Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: Significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy 2000;16:677694. 4. Burkhart SS, Debeer JF, Tehrany AM, Parten PM. Quantifying glenoid bone loss arthroscopically in shoulder instability. Arthroscopy 2002;18:488-491. 5. Lo IK, Parten PM, Burkhart SS. The inverted pear glenoid: An indicator of significant glenoid bone loss. Arthroscopy 2004; 20:169-174.
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6. Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg Am 2003;85:878-884. 7. Lee SB, Kim KJ, O’Driscoll SW, Morrey BF, An KN. Dynamic glenohumeral stability provided by the rotator cuff muscles in the mid-range and end-range of motion. A study in cadavera. J Bone Joint Surg Am 2000;82:849-857. 8. Burkhart SS, Lo IK. Arthroscopic rotator cuff repair. J Am Acad Orthop Surg 2006;14:333-346. 9. Mologne TS, Provencher MT, Menzel KA, Vauchon TA, Dewing CB. Arthroscopic stabilization in patients with an inverted pear glenoid. Am J Sports Med 2007;35:1276-1283. 10. Gerber C, Nyffeler RW. Classification of glenohumeral joint instability. Clin Orthop Relat Res 2002;400:65-76. 11. Millett PJ, Clavert P, Warner JJ. Open operative treatment for anterior shoulder instability: When and why? J Bone Joint Surg Am 2005;87:419-432. 12. 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. 13. Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: A cadaveric study. J Bone Joint Surg Am 2000;82:35-46.
14. Saito H, Itoi E, Sugaya H, Minagawa H, Yamamoto N, Tuoheti Y. Location of the glenoid defect in shoulders with recurrent anterior dislocation. Am J Sports Med 2005;33:889-893. 15. Warner JP, Gill TJ, O’Hollerhan JD, Pathare N, Millett PJ. Anatomical glenoid reconstruction for recurrent anterior glenohumeral instability with glenoid deficiency using an autogenous tricortical iliac crest bone graft. Am J Sports Med 2006;34:205-212. 16. 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. 17. Kwon YW, Powell KA, Yum JK, Brems JJ, Iannotti JP. Use of three-dimensional computed tomography for the analysis of the glenoid anatomy. J Shoulder Elbow Surg 2005;14:85-90. 18. Kralinger F, Aigner F, Longato S, Rieger M, Wambacher M. Is the bare spot a consistent landmark for shoulder arthroscopy? A study of 20 embalmed glenoids with 3-dimensional computed tomographic reconstruction. Arthroscopy 2006;22: 428-432. 19. Burkhart SS, DeBeer JF, Barth JR, et al. Results of modified Latarjet reconstruction in patients with anteroinferior instability and significant bone loss. Arthroscopy 2007;23:1033-1041. 20. Burkhart SS. The bare spot of the glenoid. Arthroscopy 2007; 23:449.
Purpose: The purpose of this study was to determine if three-dimensional computed tomography (3-D CT) scans of the glenoid can be used to accurately quantify, by means of a glenoid index, bone loss in patients with anterior glenohumeral instability, and to compare the results with arthroscopic measurements to determine if the 3-D CT scan can preoperatively predict which patients with anterior glenohumeral instability will benefit from a bone grafting procedure. Methods: From 2003 to 2006, 188 patients with anterior glenohumeral instability underwent arthroscopic evaluation and treatment by the senior author (S.S.B.). Of 188 total patients, there were 25 patients ranging in age from 15 to 43 years (median, 19 years) who underwent 3-D CT evaluations of both shoulders followed by arthroscopy of the unstable shoulder. For an arthroscopically measured bone loss of less than 25% of the inferior glenoid diameter, an arthroscopic Bankart repair was performed; for a glenoid bone loss of greater than or equal to 25%, an open Latarjet reconstruction was performed. We defined the glenoid index as the ratio of the maximum inferior diameter of the injured glenoid compared to the maximum inferior diameter of the uninjured contralateral glenoid as calculated from the 3-D CT scans. If the glenoid index was greater than 0.75, the patient was predicted to benefit from an arthroscopic Bankart repair (the need for surgery and the type of surgery having been determined on the basis of arthroscopic measurements). However, if the glenoid index was less than or equal to 0.75, the patient was predicted to benefit from an open Latarjet procedure. The results of each patient’s glenoid index were compared with the arthroscopic decision to perform either an arthroscopic Bankart repair or an open Latarjet procedure. Results: Of the 25 patients included in this study, 13 patients underwent an open Latarjet procedure and 12 patients underwent an arthroscopic Bankart repair. The 3-D CT scans accurately predicted the arthroscopic decisions to perform an arthroscopic Bankart repair or open Latarjet in 24 (96%) of 25 cases (Fisher exact test; P ⬍ .001). Conclusions: The glenoid index as calculated from the 3-D CT scan accurately predicted the requirement of a bone grafting procedure for 24 (96%) of 25 patients when the benchmark value of 0.75 was used. The 3-D CT scan can therefore be used by surgeons as an additional diagnostic tool for preoperative planning and patient counseling. Level of Evidence: Level III, development of diagnostic criteria with universally applied reference (nonconsecutive patients). Key Words: Bankart repair—Bone graft— Computed tomography—Glenoid index—Instability—Shoulder arthroscopy—Shoulder instability.
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e believe that the treatment of anterior glenohumeral instability with significant bone loss requires a bone grafting procedure to prevent the
From The San Antonio Orthopaedic Group, San Antonio, Texas, U.S.A. S.S.B. is a consultant for, and receives royalties from, Arthrex, Inc. The other authors report no conflict of interest. Address correspondence and reprint requests to Stephen S. Burkhart, M.D., 400 Concord Plaza Dr, Ste 300, San Antonio, TX 78216, U.S.A. E-mail: [email protected] © 2008 by the Arthroscopy Association of North America 0749-8063/08/2404-7372$34.00/0 doi:10.1016/j.arthro.2007.10.008
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recurrence of instability or dislocation and ultimately to improve the clinical outcome.1-3 The difficulty lies in determining the amount of bone loss that represents a clinically significant deficit. The arthroscopic appreciation of an inverted pear–shaped glenoid and quantification of the amount of glenoid bone loss using the glenoid bare spot as a reference point have been previously described as accurate and well-accepted guides to determine significant bone loss.3-5 Burkhart and DeBeer3 showed that in patients with anterior glenohumeral instability and an inverted pear– shaped glenoid, which represents a loss of greater than
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 24, No 4 (April), 2008: pp 376-382
PREOPERATIVE 3-D CT TO QUANTIFY GLENOID BONE LOSS 25% of the maximum inferior glenoid width, the recurrence rate of shoulder instability or dislocation after an arthroscopic Bankart repair was 67%. However, patients with less than 25% loss of the maximum inferior glenoid width had a recurrence rate of only 4%. Three-dimensional computed tomography (3-D CT) has been used for measuring bone loss in patients with anterior glenohumeral instability.6 However, to our knowledge, there have been no CT studies in the literature that quantify anterior glenoid bone loss and compare it to the measured bone loss with an arthroscopically validated method. In this study, we used 3-D CT imaging of both the injured and intact shoulders to measure the amount of glenoid bone loss in the injured shoulder. We then compared the CT measurements and CT-derived glenoid index to the direct arthroscopic measurements and arthroscopically derived glenoid index of patients who underwent treatment for anterior glenohumeral instability. If the arthroscopically derived glenoid index was greater then 0.75, then an arthroscopic Bankart repair was done. If the arthroscopically derived glenoid index was less than 0.75, then an open Latarjet procedure with coracoid bone grafting of the glenoid was performed. All surgical treatment decisions were based on the arthroscopic findings and measurements. We compared the CT-derived glenoid index of each patient with the arthroscopically derived glenoid index. We hypothesized that the 3-D CT– derived glenoid index would correlate well with the arthroscopically derived glenoid index and that the CT measurements would therefore be useful in accurately predicting the preferred treatment (arthroscopic Bankart repair v open bone grafting). METHODS The study was done with institutional approval as per the research requirements of The Orthopaedic Institute in San Antonio, Texas. From 2003 to 2006, 188 patients with anterior glenohumeral instability underwent arthroscopic evaluation and treatment by the senior author (S.S.B.). All of these patients had diagnostic arthroscopic evaluations of their shoulders to determine the morphology of their glenoids. Through a standard anterosuperolateral viewing portal the glenoids were viewed en face and classified as either pear-shaped or inverted pear–shaped. Furthermore, the amount of glenoid bone loss was quantified arthroscopically using a validated methodology based on the glenoid bare spot, which is the center of the inferior glenoid circle.4
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Of the 188 patients, there were 25 nonconsecutive patients ranging in age from 15 to 43 years (median, 19 years) who underwent 3-D CT evaluations of both of their shoulders. The scans were done by a General Electric Lightspeed Ultra (Milwaukee, WI) with 8-slice scans converted to 3-D CT reconstructions by combined standard and bone algorithms. Our criteria for obtaining a 3-D CT scan were: (1) at least 3 known shoulder dislocations; (2) total duration of all dislocations more than 4 hours; or (3) suspicion of significant bone loss on plain films or magnetic resonance imaging. A linear method was used to calculate the amount of bone loss of the injured glenoid compared to the uninjured contralateral glenoid with the 3-D CT scans. The first step in the process was obtaining an en face view of the uninjured glenoid with the 3-D CT scan. The most superior aspect of the glenoid is just posterior to the base of the coracoid and is labeled as A1 (Fig 1A). The most inferior aspect of the glenoid is the farthest point from A1 and usually corresponds with the lateral ridge of the scapular body. This point is labeled B1. A line is then drawn connecting A1 to B1 (labeled A1B1 in Fig 1A). The line A1B1 corresponds to the normal glenoid height (H1) of the uninjured shoulder (A1B1 ⫽ H1). The second line drawn (C1D1) is perpendicular to A1B1 and is adjusted up or down until it is at the widest portion of the inferior glenoid (Fig 1B). The line C1D1 corresponds to the normal inferior glenoid width (W1) of the uninjured shoulder (C1D1 ⫽ W1). The intersection of lines A1B1 and C1D1 is labeled O1 (Fig 1C), which represents the geometric center of the inferior glenoid circle (Fig 1D). The line O1D1 corresponds to the radius of the normal inferior glenoid circle (R1) of the uninjured shoulder (O1D1 ⫽ R1). An en face view of the injured glenoid is then obtained. The length of the glenoid is measured in a similar fashion as the uninjured glenoid and line A2B2 (H2) is drawn (Fig 2A). We made the assumption that the injured glenoid with the Bankart lesion had morphology identical to the uninjured glenoid before the injury.6 The radius of the inferior glenoid circle was then calculated through basic proportions. Because R1/H1 ⫽ R2/H2, R2 could be calculated by the following formula: R2 ⫽ (R1/H1)*H2. Therefore, the geometric center of the inferior glenoid circle (O2) could be found a distance equal to R2 from the point B2 (Fig 2B). A new line is drawn that crosses point O2 and is perpendicular to line A2B2. This line is labeled C2D2 (Fig 2C) and represents the inferior width of the
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FIGURE 1. Normal glenoid, left shoulder. (A) The long axis of the glenoid is defined by line A1B1. (B) The widest portion of the inferior glenoid is line C1D1, which is perpendicular to line A1B1. (C) The intersection of lines A1B1 and C1D1 is labeled O1, and it represents the geometric center of the inferior glenoid circle (D).
injured glenoid (W2). A virtual inferior glenoid circle can be drawn on the injured glenoid which clearly shows the amount of anteroinferior glenoid bone loss (Fig 2D). The predicted preinjury width of the injured glenoid (W2=) can then be calculated with the following formula: W2= ⫽ (W1/H1)*H2. This calculation normalizes the preinjury width by accounting for any height difference between the injured and uninjured glenoid. The glenoid index is then calculated as the ratio of the postinjury width of the injured glenoid to the preinjury width of the uninjured glenoid. It was calculated through the following formula: glenoid index ⫽ W2/W2=. Therefore, the 3-D CT scan was used to calculate a glenoid index for each patient. Because it has been determined that patients with bone loss comprising less than 25% of the inferior glenoid diameter do well with an arthroscopic Bankart repair alone, we have used a glenoid index of 0.75 as our threshold for predicting which patients would benefit from a bone grafting procedure.3
If the glenoid index was greater than 0.75, the patient was predicted to do well with an arthroscopic Bankart repair without bone grafting. However, if the glenoid index was less than or equal to 0.75, the patient was predicted to require an open Latarjet procedure in order to restore optimal stability. Each patient’s glenoid index was correlated with the arthroscopic decision to perform either an arthroscopic Bankart repair or an open Latarjet procedure (Tables 1 and 2). Our decision to perform an arthroscopic stabilization versus open bone grafting was based solely on the arthroscopic findings and arthroscopic measurements of bone deficiency. RESULTS Of the 25 patients included in this study, 13 patients underwent an open Latarjet procedure and 12 patients underwent an arthroscopic Bankart repair. Based on the procedural diagnostic benchmark of 0.75 for the glenoid index, 12 (92%) of the 13 patients who un-
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FIGURE 2. Injured glenoid with anteroinferior bone loss, right shoulder. In (A), (B), and (C), lines are drawn as in Figure 1 to represent the height (A2B2) and maximum inferior glenoid width (C2D2). The intersection of these two lines at point O2 defines the geometric center of the inferior glenoid circle before bone loss, so that the amount of bone loss is readily apparent in (D) as the vacant area that is anterior to C2 within the glenoid circle.
derwent an open Latarjet procedure and all 12 of the patients who underwent an arthroscopic Bankart repair were correctly classified, so that a total of 24 (96%) of 25 procedures were accurately predicted TABLE 1.
(Fisher exact test; P ⬍ .001). For the correctly classified cases, the glenoid index ranged from 0.577 to 0.747 (median, 0.668) for open Latarjet procedures and from 0.847 to 0.964 (median, 0.914) for arthro-
Details of the 13 Patients Who Underwent an Open Latarjet Procedure
Case No.
Age (yrs)
H1
W1
R1
H2
R2
W2
W2=
3-D CT Glenoid Index
1 2 3 4 5 6 7 8 9 10 11 12 13
24 21 19 17 21 24 27 41 16 19 24 21 19
3.4 3.7 2.4 3.4 2.7 2.5 2.25 2.2 2.05 6.2 6 5.8 2.5
2.35 2.95 1.8 2.6 2.4 2.1 1.95 1.9 1.5 5 4.4 4 1.8
1.2 1.5 0.9 1.3 1.2 0.9 0.9 1 0.8 2.5 2.3 2.05 0.9
2.9 4.4 2.5 3.4 2.7 3.4 2.6 2.4 1.9 6.3 6.4 9.0 3.2
1.02 1.78 0.94 1.30 1.20 1.22 1.04 1.09 0.74 2.54 2.45 3.18 1.15
1.7 2.4 1.4 1.7 1.6 2 1.3 1.2 1 3.4 3 3.8 1.7
2.00 3.51 1.88 2.60 2.40 2.86 2.25 2.07 1.39 5.08 4.69 6.21 2.30
0.848 0.684 0.747 0.654 0.667 0.700 0.577 0.579 0.719 0.669 0.639 0.612 0.738
NOTE. The units for height (H), width (W), and radius (R) were measured in centimeters (cm). Abbreviation: 3-D CT, three-dimensional computed tomography.
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Details of the 12 Patients Who Underwent an Arthroscopic Bankart Repair
Case No.
Age (yrs)
H1
W1
R1
H2
R2
W2
W2=
3-D CT Glenoid Index
1 2 3 4 5 6 7 8 9 10 11 12
43 17 15 19 16 24 26 21 19 16 18 17
2.35 2.1 2.2 2.9 2.5 1.8 2.2 5.3 2.3 8 2.7 2.6
1.6 1.7 1.9 2.2 1.7 1.4 1.55 3.7 1.55 6.1 1.9 2
0.85 0.85 1 1.05 0.9 0.65 0.8 1.9 0.9 3.1 1 1.1
1.9 2.3 2.2 2.8 2.6 1.8 1.95 5.8 2.5 7.1 2.7 2.6
0.69 0.93 1.00 1.01 0.94 0.65 0.71 2.08 0.98 2.75 1.00 1.10
1.2 1.7 1.8 1.8 1.55 1.35 1.2 3.7 1.5 5 1.75 1.7
1.29 1.86 1.90 2.12 1.77 1.40 1.37 4.05 1.68 5.41 1.90 2.00
0.928 0.913 0.947 0.847 0.877 0.964 0.873 0.914 0.890 0.924 0.921 0.850
NOTE. Height (H), width (W), and radius (R) were measured in centimeters.
scopic Bankart repairs. The incorrectly classified open Latarjet procedure had a glenoid index of 0.848. This value was twice as far from the median as any other value for open Latarjet procedures, so the glenoid index for this case was a statistical outlier. This patient has done well with the open Latarjet procedure, and we are confident that our arthroscopic measurement criteria accurately assigned this patient to the open Latarjet group. We believe that in this patient, the CT scan did not accurately show the bone loss because of a technical or artifactual problem with the scan. DISCUSSION Anterior glenohumeral stability is dependent upon balanced soft tissues and a full concentric arc of bony support. After an anterior glenohumeral dislocation, the value of such structures becomes obvious. The importance of balanced soft tissues both anteriorly and posteriorly has been well established in the literature.7,8 The need for a sufficient glenoid base to support a full arc of motion is generally accepted; however, the amount of anterior glenoid bone required to prevent future anterior instability is still being elucidated. One recent study suggested that glenoid bone loss in the 20% to 30% range can be addressed by arthroscopic Bankart repair.9 These authors reported a 13.3% rate of recurrent instability at a mean follow-up of 34 months, while other studies have suggested that a loss of more than 20% to 25% of the inferior glenoid width predisposes a patient to future anterior instability.2,3,10-13 In such cases, a bone grafting procedure may be a necessary adjuvant procedure to increase the glenohumeral stability and prevent future recurrences of anterior subluxations or dislocations.2,3,6,10,14,15
The prevalence of glenoid lesions after an anterior glenohumeral dislocation is quite variable in the literature.6,13,14 The variability may be caused by different patient populations, imaging modalities, and/or the variable expression of glenoid lesions. Sugaya et al.6 evaluated 100 patients with recurrent anterior instability and found that 90% of them had glenoid lesions on 3-D CT scans; however, only 50% of them had osseous fragments while the remaining 40% had changes to the anterior glenoid rim consistent with compression. The CT scan with 3-D reconstructions provides the surgeon with a bony model to evaluate the glenoid rim morphology.6,14,16,17 However, to date there have been no CT studies in the literature that quantify anterior glenoid bone loss and compare it to glenoid bone loss determined by an arthroscopically validated method. Burkhart et al.4 arthroscopically evaluated the glenoid bare spot in 56 patients with no evidence of instability.4 The investigators measured the distance from the bare spot to the anterior, posterior, and inferior glenoid margins. The glenoid bare spot was consistently found to be at the center of a virtual circle of the inferior glenoid. The bare spot was shown to be a consistent, reliable marker that can be used arthroscopically to quantify the amount of anterior glenoid bone loss. A recent study by Kralinger et al.18 suggests that the bare spot of the glenoid might not consistently be located at the center of the inferior glenoid, and therefore might not be a good landmark for calculating glenoid bone loss. However, their cadaveric study was performed on embalmed specimens with an average age of 81.6 years, introducing the possibility of artifactual error from embalming and from the potentially
PREOPERATIVE 3-D CT TO QUANTIFY GLENOID BONE LOSS high anatomic variation related to the extreme age of the specimens.19 In contradistinction, the study by Burkhart et al.20 was performed in young live healthy subjects in which the glenoid bare spot was identified and directly measured arthroscopically. Recognizing this controversy, we believe that the arthroscopic measurements in young live individuals have the least likelihood of introducing artifactual error, and therefore we believe we are justified in basing our treatment decisions on these arthroscopic measurements. The normal appearance of a glenoid is pear-shaped with the inferior portion of the glenoid being wider than the superior portion. After an anterior dislocation, a significant loss of anterior–inferior glenoid bone can result in an inverted pear-shaped glenoid. Lo et al.5 arthroscopically evaluated 53 patients with anterior instability and used the bare spot to determine the amount of inferior glenoid bone loss that is necessary to create an inverted pear-shaped glenoid. Furthermore, 6 fresh-frozen cadaveric specimens were sequentially cut to determine the amount of bone loss required to create an inverted pear-shaped glenoid. The results show that a loss of 25% of the inferior glenoid width arthroscopically or 27% of the inferior glenoid width in the cadaveric glenoids resulted in the appearance of an inverted pear-shaped glenoid. Therefore, a loss of 25% to 27% of the inferior glenoid width results in the appearance of an inverted pear-shaped glenoid. Burkhart and DeBeer3 analyzed the results of 194 consecutive arthroscopic Bankart repairs by a suture anchor technique for traumatic anterior glenohumeral instability. The investigators discovered that if there was no significant glenoid bone loss (pear-shaped glenoid) the recurrence rate for subluxation or dislocation was 4%; however, if there was significant bone loss (inverted pear–shaped glenoid) the recurrence rate was 67%. Their study concluded that patients with significant glenoid bone loss require a bone grafting procedure (e.g., Latarjet procedure) to decrease the rate of recurrent subluxation or dislocation. The authors subsequently changed their approach to patients with anterior glenohumeral instability. In their revised approach, the patients had their inferior glenoid widths measured arthroscopically (based on the glenoid bare spot) at the beginning of every instability case. All patients with glenoid bone loss of 25% or more of the inferior glenoid diameter (glenoid index, ⱕ0.75) were treated with an open Latarjet procedure. In a subsequent study, the authors tested their new clinical approach and found that their patients with a Latarjet procedure had a recurrence rate of only 4.9%.20 This result was far better than their earlier
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arthroscopic Bankart recurrence rate of 67% in patients with a similar degree of glenoid bone deficiency. It is now established that patients without significant glenoid bone loss who undergo an arthroscopic Bankart repair can expect a recurrence rate under 5%.3 Similarly, patients who undergo an open Latarjet procedure for significant glenoid bone loss can also expect a recurrence rate under 5%.20 There were several limitations of our study. Although the arthroscopic glenoid bare spot has been shown by our senior author to be a very reliable marker for the center of the inferior glenoid, it is not known whether the arthroscopic or the 3-D CT scan measurement is the true gold standard. Secondly, we used an en face view with our 3-D CT scan. The acquisition of such a view is operator-dependent. Furthermore, all of our measurements were manual (without the aid of computer software), which could introduce human error.
CONCLUSIONS The glenoid index as calculated from the 3-D CT scan accurately predicted the requirement of a bone grafting procedure for 24 (96%) of 25 patients when the benchmark value of 0.75 was used. The 3-D CT scan can therefore be used by surgeons as an additional diagnostic tool for preoperative planning and patient counseling. Acknowledgment: The authors thank John D. Schoolfield, M.S., for his statistical analysis and assistance with the preparation of the manuscript.
REFERENCES 1. Latarjet M. Techniques in the treatment of recurrent dislocation of the shoulder. Lyon Chir 1965;61:313-318. 2. Bigliani LU, Newton PM, Steinmann SP, Connor PM, Mcllveen SJ. Glenoid rim lesions associated with recurrent anterior dislocation of the shoulder. Am J Sports Med 1998; 26:41-45. 3. Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: Significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy 2000;16:677694. 4. Burkhart SS, Debeer JF, Tehrany AM, Parten PM. Quantifying glenoid bone loss arthroscopically in shoulder instability. Arthroscopy 2002;18:488-491. 5. Lo IK, Parten PM, Burkhart SS. The inverted pear glenoid: An indicator of significant glenoid bone loss. Arthroscopy 2004; 20:169-174.
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6. Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg Am 2003;85:878-884. 7. Lee SB, Kim KJ, O’Driscoll SW, Morrey BF, An KN. Dynamic glenohumeral stability provided by the rotator cuff muscles in the mid-range and end-range of motion. A study in cadavera. J Bone Joint Surg Am 2000;82:849-857. 8. Burkhart SS, Lo IK. Arthroscopic rotator cuff repair. J Am Acad Orthop Surg 2006;14:333-346. 9. Mologne TS, Provencher MT, Menzel KA, Vauchon TA, Dewing CB. Arthroscopic stabilization in patients with an inverted pear glenoid. Am J Sports Med 2007;35:1276-1283. 10. Gerber C, Nyffeler RW. Classification of glenohumeral joint instability. Clin Orthop Relat Res 2002;400:65-76. 11. Millett PJ, Clavert P, Warner JJ. Open operative treatment for anterior shoulder instability: When and why? J Bone Joint Surg Am 2005;87:419-432. 12. 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. 13. Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: A cadaveric study. J Bone Joint Surg Am 2000;82:35-46.
14. Saito H, Itoi E, Sugaya H, Minagawa H, Yamamoto N, Tuoheti Y. Location of the glenoid defect in shoulders with recurrent anterior dislocation. Am J Sports Med 2005;33:889-893. 15. Warner JP, Gill TJ, O’Hollerhan JD, Pathare N, Millett PJ. Anatomical glenoid reconstruction for recurrent anterior glenohumeral instability with glenoid deficiency using an autogenous tricortical iliac crest bone graft. Am J Sports Med 2006;34:205-212. 16. 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. 17. Kwon YW, Powell KA, Yum JK, Brems JJ, Iannotti JP. Use of three-dimensional computed tomography for the analysis of the glenoid anatomy. J Shoulder Elbow Surg 2005;14:85-90. 18. Kralinger F, Aigner F, Longato S, Rieger M, Wambacher M. Is the bare spot a consistent landmark for shoulder arthroscopy? A study of 20 embalmed glenoids with 3-dimensional computed tomographic reconstruction. Arthroscopy 2006;22: 428-432. 19. Burkhart SS, DeBeer JF, Barth JR, et al. Results of modified Latarjet reconstruction in patients with anteroinferior instability and significant bone loss. Arthroscopy 2007;23:1033-1041. 20. Burkhart SS. The bare spot of the glenoid. Arthroscopy 2007; 23:449.