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Quantification of a glenoid defect with three-dimensional computed tomography and magnetic resonance imaging: A cadaveric study
Quantification of a glenoid defect with three-dimensional computed tomography and magnetic resonance imaging: A cadaveric study Pol E. Huijsmans, MD,a Pieter S. Haen,b Martin Kidd, PhD,c Wouter J. Dhert, MD, PhD,b Victor P. M. van der Hulst, MD, PhD,d and W. Jaap Willems, MD, PhD,a Amsterdam and Utrecht, The Netherlands; and Stellenbosch, South Africa
Bone loss of the glenoid is a common finding in anterior glenohumeral instability. Several methods to measure the size of a glenoid defect have been described but have not been validated. In this study, 14 cadaver glenoids with a randomly created anteroinferior glenoid defect were used for validation of the so-called circle method. Measurements were done by 2 researchers on digital photographs, 3-dimensional (3D) computed tomography (CT) scans, and magnetic resonance images (MRI). The correlation coefficient (r2) for comparing measurements from the digital photographs with the CT scans was 0.97 for researcher 1 and 0.90 for researcher 2. When they compared digital images with MRI, the r2 was 0.93 for researcher 1 and 0.92 for researcher 2. No statistical differences were found between the 2 researchers. The circle method is a simple method for preoperative quantification of a glenoid defect. Measurements can be done with 3D CT scans as well as MRI. (J Shoulder Elbow Surg 2007;16:803-809.)
A defect, erosion, or fracture of the bony glenoid
rim is a common finding in anterior shoulder instability.3,4,8,12,27,29,30,32 Laboratory and clinical studies have shown that these defects can influence the outcome of treatment for recurrent anterior glenohumeral instability and changes the biomechanics of the glenohumeral joint.3,4,10,11,16,19,22,31,33 However, there is no consensus regarding the exact role of a glenoid defect in glenohumeral instability.
Itoi et al16 showed in a cadaver study that a defect of more than 21% of the length of the glenoid requires bone grafting to obtain a stable glenohumeral joint. Burkhart and DeBeer4 demonstrated that patients with an inverted pear-shaped glenoid due to bone loss are very unstable and should be treated with bone grafting. The amount of bone loss to produce an inverted pear-shaped glenoid is at least 25% of the original maximum width.17 To investigate the role of a bony defect of the glenoid in glenohumeral instability further, more research is needed, especially clinical studies. Sugaya et al29 published a method to quantify the size of a glenoid defect in patients with preoperative anterior glenohumeral instability. Their measurements were done using 3-dimensional (3D) computed tomography (CT) scans by calculating the missing part of a digitally drawn circle on the sagittal view of the glenoid. In a previous study, we validated and confirmed the observation by Sugaya et al regarding the inferior part of the glenoid having the shape of a true circle.14 Although CT is known to be the modality of choice to detect bony abnormalities in glenohumeral instability,27 magnetic resonance imaging (MRI) arthrography is widely used as the modality of choice preoperatively for capsulolabral, rotator cuff, and cartilage lesions.1,2,6,9,18,21,28,36,37 The purpose of the current study was to validate the method used by Sugaya29 and to determine if MRI imaging can be used for measuring bone loss of the glenoid. MATERIALS AND METHODS
From the aDepartments of Orthopaedics and Traumatology, and dRadiology, Onze Lieve Vrouwe Gasthuis; bDepartment of Orthopaedics, University Medical Center Utrecht; and the cCentre for Statistical Consultation, University of Stellenbosch. Reprint requests: W. Jaap Willems, MD, PhD, Department of Orthopaedics and Traumatology, Onze Lieve Vrouwe Gasthuis, 1e Oosterparkstraat 279, 1091 HA Amsterdam, The Netherlands. (E-mail: [email protected]). Copyright © 2007 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2007/$32.00 doi:10.1016/j.jse.2007.02.115
This study used 8 formaldehyde-preserved scapulae and 6 fresh-frozen scapulae from skeletally mature individuals. Scapulae with a bony defect or erosion of the glenoid were excluded. A 3D CT scan (AVE 1 Philips Tomoscan, 125 mA, 120 kV, 1 second; field of view, 120 mm; filter, 1H; slice, 1 mm; table speed, 1 mm/s; reconstruction index, 1 mm; Philips Medical Systems, Best, The Netherlands) and an MRI scan (3D T1-weighted, fast field echo, echo planer imaging, Matrix 256*256, 0.5 mm slice thickness; echo time, 13.8 milliseconds; repetition time, 55; flip angle, 55) were made
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Figure 1 Digital photograph of sagittal view of a glenoid with created anterior defect. The missing part of the drawn circle (B) represents the size of the defect.
of each scapula. Reconstructions were made from 3D CT images, and the exact sagittal view of the glenoid was used for measurements. The volume MRI scan permitted obtaining the exact, most lateral sagittal view of the glenoid, which was used for measurements. The scapulae were cleared of soft tissue, including the labrum, and placed in a clamp. A digital photograph (Sony Digital camera, 1.3 megapixel, Sony, Japan) was made of the sagittal view of the glenoid with a caliper next to the surface to indicate its relative size. These predefect scans and photographs were used to confirm the circle shape of the inferior glenoid. With an electric saw, a defect was created at the anterior or anteroinferior aspect of the glenoid. The size and location of the defect were chosen randomly by one of the researchers. Again, a digital photograph and 3D CT and MRI scans were made. Sagittal views of the glenoid were used for analysis and measurements. The images were filed in a tagged image file (TIF) format and analyzed using OSIRIS 4.17 software (University of Geneva, Switzerland). The images were calibrated for their relative size. A circle was placed on the inferior part of the glenoid using the digital analysis software. The best fitting circle on
the inferior glenoid, according to the researchers, was used. The outer cortex of the inferior glenoid on the sagittal view was selected to be the landmark for circle placement. In a previous study, we demonstrated that the shape of the inferior part of the bony glenoid has the shape of a true circle.14 Therefore, when a circle was placed on the inferior part of the glenoid on the digital photograph and CT and MRI scan, the missing part of that circle should represent the size of the created defect. The surface of the circle and the surface of the missing part of that circle were measured (mm2). The size of the defect was calculated using the following formula, which was also used by Sugaya et al29: [(Surface B/Surface A) ⫻ 100%] (Figures 1, 2, and 3). All measurements were done by 2 independent researchers. Each measurement was repeated 3 times and the averages were used for statistical analysis.
Statistical analysis For analysis of the reliability and conformity of the findings of both researchers for the different imaging modalities, scatter plots were made, and the correlation coef-
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Figure 2 Sagittal view of a 3-dimensional computed tomography reconstruction of the same glenoid as in Figure 1. The missing part of the circle (B) represents the size of the glenoid defect.
ficient (r2) was calculated. To analyze the differences of the measurements between the two researchers and between the different imaging modalities, Bland-Altman plots were made, and mean differences, maximum differences, and standard deviations were calculated. Repeated measures analysis of variance was used to detect significant differences between the measurements of the 2 researchers and for the different imaging modalities. A 5% significance level (P ⬍ .05) was used as a guideline for detecting significant differences.
RESULTS The MRI and CT images showed no difference in quality or appearance between the fresh and embalmed scapulae. All specimens had an exact circleshaped inferior glenoid on the digital photograph and CT and MRI scans before the defect was created. The measurements of the size of the glenoid defect taken from the different imaging modalities by the 2 researchers were analyzed. Figures 4, A and B show Bland-Altman plots for the comparison of the measurements taken from the digital photograph and the measurements taken from the CT scans for researcher. The 95% confidence interval for the difference in glenoid defect size measurements taken from CT scans compared with the measurements taken from
the digital photographs was 4.11% for researcher 1 and 8.06% for researcher 2. The r2 was 0.97 for researcher 1 and 0.90 for researcher 2. None of the measurements of researcher 1 showed a difference of more than 4%. Only 2 of the 14 measurements done by researcher 2 showed a difference between the measurements of more than 5.5%. Figure 5, A and B show Bland-Altman plots for the comparison of the digital photograph measurements with the MRI measurements for each researcher. The difference between the measurements taken from the MRI scans and the measurements taken from the digital photographs demonstrates a 95% confidence interval of 6.51% for researcher 1 and 8.11% for researcher 2. Only 1 measurement done by researcher 1 showed a difference in the measured size of the glenoid defect of more than 4.5%. Of the 14 measurements done by researcher 2, 12 showed a difference of less than 6%. The correlation between these two image modalities showed a r2 of 0.93 for researcher 1 and 0.92 for researcher 2. An overview of the mean differences, maximum differences, and standard deviations for the comparison of the measurements taken from the different image modalities for each researcher is summarized
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Figure 3 A sagittal view magnetic resonance scan of same glenoid as in Figure 1. Area B represents the glenoid defect.
in Table I. When the measurements of the 2 researchers were compared, the interobserver reliability for the measurements of the size of the glenoid defect taken from the digital photographs showed an r2 of 0.97, with a standard deviation of 2.36%. The interobserver reliability for the CT scan measurements shows an r2 of 0.94. Only 1 defect measurement on a CT scan showed a difference of more than 3% between the 2 researchers. The r2 for the measurements done by the 2 researchers on the MRI scans was 0.87. Of the 14 MRI measurements, 11 showed a difference between the 2 researchers of less than 4.5%. The maximum difference in the measurement of the size of a glenoid defect on MRI between the 2 researchers was 10.77%. Table II gives an overview of the comparison of the measurements of the size of glenoid done by the 2 researchers for each image modality. Mean difference, maximum difference, standard deviation, and the r2 are noted. Paired t tests showed no statistical significant differences between the measurements done on the different image modalities for each researcher. No statistical differences were found between the measurements of the 2 researchers.
DISCUSSION Although it is well known that a defect or erosion from the anteroinferior glenoid rim is a common finding in glenohumeral instability,3,4,8,12,17,24,27,29,32 the exact role of this finding is still being discussed. Some authors found a relationship between the presence and size of a glenoid defect and redislocation after Bankart repair,3,4,16,22,23,31,33 but others could not confirm this relationship.13,20,24 Future prospective studies are needed to investigate this particular subject objectively in anterior glenohumeral instability. To perform such studies, a validated and generally accepted method for measuring the size of a glenoid defect is needed. Different ways to measure the size of a glenoid defect have been described in the literature. Bigliani3 described the size of the glenoid rim fracture as a percentage of the original width of the inferior glenoid. Ungersbock et al33 described the size of a glenoid defect in millimeters of the width of the defect. Gerber and Nyffeler10 showed a decrease in dislocation resistance of more than 30% if the glenoid rim lesion measured more than half of the maximal anteroposterior diameter of the glenoid fossa. This quan-
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Figure 4 Differences in measurements (%) of the glenoid defect on 3-dimensional computed tomography images (CT) compared with the “actual” size on the digital photograph (DP). A, Results for researcher 1. B, Results for researcher 2.
Figure 5 Differences in measurements (%) of the glenoid defect on magnetic resonance images (MRI) compared with the “actual” size on the digital photograph (DP). A, Results for researcher 1. B, Results for researcher 2.
tification method was used by Warner et al35 in a clinical study. Burkhart et al5 published a method for quantifying a glenoid defect arthroscopically with a special caliper. With this method, an arthroscopic caliper is placed in the center of the bare spot of the inferior glenoid. From this point, the distance to the posterior labrum and the anterior glenoid rim are measured and compared. The difference between these 2 distances in millimeters represents the size of the glenoid defect. Other studies mention bony Bankart lesions but do not give a quantification of the defect.22,32 Three studies on preoperative measurement of a glenoid defect have recently been published.12,15,29 Itoi et al16 showed in a cadaver study that a defect of 21% of the glenoid length requires bone grafting. To address the problem of defect measurement preoperatively, they published a study on quantification of the defect.15 CT scans and West point view radiographs were used to determine the size of a glenoid defect.
They found that a defect of 21% of the length of the glenoid appeared was 18.6% of the intact width on a West point view and 50% of the intact width of a slice of the lower one fourth on the CT image. The drawback of their study is that a standard osteotomy was made anteroinferiorly, and this does not address measurements for more anteriorly located defects. Second, with this method the measurements have to be compared with the normal width of the glenoid on the contralateral side. This can be a problem in patients with bilateral instability or congenital asymmetry of the scapulae. In 2003, Griffith et al12 published a study for measurement of a glenoid defect with CT. They concluded that the best indicator of glenoid bone loss was the width of the glenoid and the width-to-length ratio of the glenoid, but for this method, measurements also need to be compared with measurements from the contralateral shoulder. It is also difficult to measure the length of the glenoid accurately on a sagittal reconstruction because of the difficulty determining the exact top of the glenoid.
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Table I Differences between measurements taken from different image modalities Researcher 1 Digital photos CT MRI
Researcher 2
Average (%)
Max (%)
SD (%)
r
Average (%)
Max (%)
SD (%)
r2
⫺0.81 ⫺0.61
⫺3.98 6.86
2.10 3.32
0.97 0.93
⫺1.21 0.74
8.32 8.48
4.11 4.14
0.90 0.92
2
SD, Standard deviation; r2, correlation coefficient; CT, computed tomography; MRI, magnetic resonance images.
Table II Differences for measurements of the glenoid defect between the two researchers for each image modality Images
Average differences (%)
Max difference (%)
SD (%)
r2
CT-CT MRI-MRI DIG-DIG
0.48 2.22 0.87
8.03 10.77 5.25
2.89 4.39 2.36
0.94 0.87 0.97
SD, Standard deviation; r2, correlation coefficient; CT, computed tomography; MRI, magnetic resonance imaging; DIG, digital photographs.
Sugaya et al29 described a method to measure a defect preoperatively on 3D CT images. They found a bony fragment or an erosion of the anterior glenoid rim in 90% of their patients. To use this method, it is not necessary to know the size of the original glenoid because the drawn circle on a sagittal view of the glenoid will point out the original contour of the glenoid. This can be important for patients with bilateral shoulder instability. The method described by Sugaya29 was not validated for reliability.34 In our cadaveric study, we tried to validate this circle method with 2 independent researchers. To our knowledge, no previous studies have tried to quantify a glenoid bone defect with MRI. MRI arthrography is the modality of choice in anterior glenohumeral instability, especially for showing abnormalities of the capsulolabral complex.1,7,25,28 Only a few studies mention the ability to detect bony abnormalities of the glenoid with MRI.28,36 The limitation of this study is the lack of a true gold standard that represents the actual size of the glenoid defect. To our knowledge, there is no generally accepted method of measuring the exact size of a glenoid defect. In our study design, the measurements from the digital images were the gold standard. The measurements from the digital images showed the highest correlation coefficient (r2 ⫽ 0.97) between the 2 researchers. Comparing the measurements for both researchers with the digital images, the measurements done with the CT scan showed smaller differences for researcher 1 (standard deviation, 2.10) compared with researcher 2 (standard deviation, 4.11). The differences between the MRI and the digital images were approximately the same for both re-
searchers. The CT measurements show a higher correlation between the 2 researchers than the MRI measurements. Although the differences in measurements between the 2 researchers were as high as 8.03% for the CT measurements and 10.77% for the MRI measurements, most of the differences in measurements were less than 3% for the CT and less than 4.5% for the MRI measurements. These differences in measurements can be explained by the interpretation of the borders of the glenoid rim on images from CT and MRI and the positioning of the circles by the researchers, which can be subject to discussion. We used volume MRI scans, which allowed us to select the exact sagittal view from the most lateral part of the glenoid bone. This maybe difficult in a clinical setting and therefore can be a potential source of errors. Taking the results of our study into account, claims from previous studies3,4,16,33 about the exact cutoff size of a glenoid defect as an indication for the need of a bony procedure (ie, Latarjet) are difficult for practical use. One must be aware of the error in measurements of a glenoid defect. Other limitations of this study are the limited number of investigated glenoids and the 2D measurements of the 3D surface of the glenoid. In our opinion, this last point is not very relevant because the bony surface of the glenoid is relatively flat and the radius of the glenoid socket is predominantly formed by the overlying cartilage.26 Another limitation is that we did not compare the different described quantification methods10,12,16 with the method described by Sugaya.29 Advantages of the circle method are its simplicity and that the size of the glenoid defect can be determined preoperatively without using the contralateral shoulder. Measurement of a glenoid defect with the circle method can easily be included in the radiologic protocol for CT or MRI scanning. This method is not restricted by the size or the location of a glenoid defect and can be used with CT as well as MRI. MRI can be the image modality of choice when soft-tissue structures need to be assessed as well as bony abnormalities. Measurements done with the circle method will give a good preoperative estimation of the amount of
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bone loss and can be used in future studies on the effect of bone loss of the anteroinferior glenoid in shoulder instability. We thank W. van Wolveren and S. Klomp, Department of Anatomy University of Utrecht, The Netherlands, for their help and assistance with the preparation of the cadaver specimen. We also would like to thank S. Phieltjens, Department of Radiology, Onze Lieve Vrouwe Gasthuis, Amsterdam, for his help with the making and processing of the CT and MRI scans. REFERENCES
1. Beltran J, Bencardino J, Mellado J, Rosenberg ZS, Irish RD. MR arthrography of the shoulder: variants and pitfalls. Radiographics 1997;17:1403-12. 2. Beltran J, Rosenberg ZS, Chandnani VP, Cuomo F, Beltran S, Rokito A. Glenohumeral instability: evaluation with MR arthrography. Radiographics 1997;17:657-73. 3. 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;26:41-5. 4. 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;16:677-94. 5. Burkhart SS, Debeer JF, Tehrany AM, Parten PM. Quantifying glenoid bone loss arthroscopically in shoulder instability. Arthroscopy 2002;18:488-91. 6. Chandnani VP, Gagliardi JA, Murnane TG, et al. Glenohumeral ligaments and shoulder capsular mechanism: evaluation with MR arthrography. Radiology 1995;196:27-32. 7. Chandnani VP, Yeager TD, DeBerardino T, et al. Glenoid labral tears: prospective evaluation with MRI imaging, MR arthrography, and CT arthrography. AJR Am J Roentgenol 1993;161: 1229-35. 8. Edwards TB, Boulahia A, Walch G. Radiographic analysis of bone defects in chronic anterior shoulder instability. Arthroscopy 2003;19:732-9. 9. Garneau RA, Renfrew DL, Moore TE, el Khoury GY, Nepola JV, Lemke JH. Glenoid labrum: evaluation with MR imaging. Radiology 1991;179:519-22. 10. Gerber C, Nyffeler RW. Classification of glenohumeral joint instability. Clin Orthop 2002:65-76. 11. Greis PE, Scuderi MG, Mohr A, Bachus KN, Burks RT. Glenohumeral articular contact areas and pressures following labral and osseous injury to the anteroinferior quadrant of the glenoid. J Shoulder Elbow Surg 2002;11:442-51. 12. Griffith JF, Antonio GE, Tong CW, Ming CK. Anterior shoulder dislocation: quantification of glenoid bone loss with CT. AJR Am J Roentgenol 2003;180:1423-30. 13. Guanche CA, Quick DC, Sodergren KM, Buss DD. Arthroscopic versus open reconstruction of the shoulder in patients with isolated Bankart lesions. Am J Sports Med 1996;24:144-8. 14. 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;15:759-63. 15. 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;31:112-8. 16. 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.
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17. Lo IK, Parten PM, Burkhart SS. The inverted pear glenoid: an indicator of significant glenoid bone loss. Arthroscopy 2004;20: 169-74. 18. Loew R, Kreitner KF, Runkel M, Zoellner J, Thelen M. MR arthrography of the shoulder: comparison of low-field (0.2 T) vs high-field (1.5 T) imaging. Eur Radiol 2000;10:989-96. 19. Montgomery WH Jr, Wahl M, Hettrich C, Itoi E, Lippitt SB, Matsen FA 3rd. Anteroinferior bone-grafting can restore stability in osseous glenoid defects. J Bone Joint Surg Am 2005;87: 1972-7. 20. O’Neill DB. Arthroscopic Bankart repair of anterior detachments of the glenoid labrum. A prospective study. J Bone Joint Surg Am 1999;81:1357-66. 21. Palmer WE, Brown JH, Rosenthal DI. Labral-ligamentous complex of the shoulder: evaluation with MR arthrography. Radiology 1994;190:645-51. 22. Pap G, Machner A, Heitmann D, Merk H, Neumann HW. [Recurrent luxations after arthroscopic refixation of the labrum using suture anchors in traumatic ventral shoulder luxation]. Zentralbl Chir 2001;126:199-204. 23. Rhee YG, Lim CT. Glenoid defect associated with anterior shoulder instability: results of open Bankart repair. Int Orthop 2006. Available online at: http://www.springerlink.com/content/ 25lp6878l535r5n1/. 24. Rowe CR, Patel D, Southmayd WW. The Bankart procedure: a long-term end-result study. J Bone Joint Surg Am 1978;60:1-16. 25. Sanders TG, Morrison WB, Miller MD. Imaging techniques for the evaluation of glenohumeral instability. Am J Sports Med 2000;28:414-34. 26. Soslowsky LJ, Flatow EL, Bigliani LU, Mow VC. Articular geometry of the glenohumeral joint. Clin Orthop 1992:181-90. 27. Stevens KJ, Preston BJ, Wallace WA, Kerslake RW. CT imaging and three-dimensional reconstructions of shoulders with anterior glenohumeral instability. Clin Anat 1999;12:326-36. 28. Stoller DW. MR arthrography of the glenohumeral joint. Radiol Clin North Am 1997;35:97-116. 29. Sugaya H, Moriishi J, Dohi M, Kon Y, Tsuchiya A. Glenoid rim morphology in recurrent anterior glenohumeral instability. J Bone Joint Surg Am 2003;85:878-84. 30. Sugaya H, Moriishi J, Kanisawa I, Tsuchiya A. Arthroscopic osseous Bankart repair for chronic recurrent traumatic anterior glenohumeral instability. Surgical technique. J Bone Joint Surg Am 2006;88 (suppl 1, pt 2):159-69. 31. 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;13:279-85. 32. Taylor DC, Arciero RA. Pathologic changes associated with shoulder dislocations. Arthroscopic and physical examination findings in first-time, traumatic anterior dislocations. Am J Sports Med 1997;25:306-11. 33. Ungersbock A, Michel M, Hertel R. Factors influencing the results of a modified Bankart procedure. J Shoulder Elbow Surg 1995; 4:365-9. 34. Warner JJ. Commentary & Perspective on “Glenoid Rim Morphology in Recurrent Anterior Glenohumeral Instability” by Sugaya et al. J Bone Joint Surg Am 2003;85:878-85. 35. Warner JJ, 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;34:205-12. 36. Willemsen UF, Wiedemann E, Brunner U, et al. Prospective evaluation of MR arthrography performed with high-volume intraarticular saline enhancement in patients with recurrent anterior dislocations of the shoulder. AJR Am J Roentgenol 1998;170: 79-84. 37. Wulker N, Ruhmann O. [MRI in dislocation and instability of the shoulder joint]. Orthopade 2001;30:492-501.
Bone loss of the glenoid is a common finding in anterior glenohumeral instability. Several methods to measure the size of a glenoid defect have been described but have not been validated. In this study, 14 cadaver glenoids with a randomly created anteroinferior glenoid defect were used for validation of the so-called circle method. Measurements were done by 2 researchers on digital photographs, 3-dimensional (3D) computed tomography (CT) scans, and magnetic resonance images (MRI). The correlation coefficient (r2) for comparing measurements from the digital photographs with the CT scans was 0.97 for researcher 1 and 0.90 for researcher 2. When they compared digital images with MRI, the r2 was 0.93 for researcher 1 and 0.92 for researcher 2. No statistical differences were found between the 2 researchers. The circle method is a simple method for preoperative quantification of a glenoid defect. Measurements can be done with 3D CT scans as well as MRI. (J Shoulder Elbow Surg 2007;16:803-809.)
A defect, erosion, or fracture of the bony glenoid
rim is a common finding in anterior shoulder instability.3,4,8,12,27,29,30,32 Laboratory and clinical studies have shown that these defects can influence the outcome of treatment for recurrent anterior glenohumeral instability and changes the biomechanics of the glenohumeral joint.3,4,10,11,16,19,22,31,33 However, there is no consensus regarding the exact role of a glenoid defect in glenohumeral instability.
Itoi et al16 showed in a cadaver study that a defect of more than 21% of the length of the glenoid requires bone grafting to obtain a stable glenohumeral joint. Burkhart and DeBeer4 demonstrated that patients with an inverted pear-shaped glenoid due to bone loss are very unstable and should be treated with bone grafting. The amount of bone loss to produce an inverted pear-shaped glenoid is at least 25% of the original maximum width.17 To investigate the role of a bony defect of the glenoid in glenohumeral instability further, more research is needed, especially clinical studies. Sugaya et al29 published a method to quantify the size of a glenoid defect in patients with preoperative anterior glenohumeral instability. Their measurements were done using 3-dimensional (3D) computed tomography (CT) scans by calculating the missing part of a digitally drawn circle on the sagittal view of the glenoid. In a previous study, we validated and confirmed the observation by Sugaya et al regarding the inferior part of the glenoid having the shape of a true circle.14 Although CT is known to be the modality of choice to detect bony abnormalities in glenohumeral instability,27 magnetic resonance imaging (MRI) arthrography is widely used as the modality of choice preoperatively for capsulolabral, rotator cuff, and cartilage lesions.1,2,6,9,18,21,28,36,37 The purpose of the current study was to validate the method used by Sugaya29 and to determine if MRI imaging can be used for measuring bone loss of the glenoid. MATERIALS AND METHODS
From the aDepartments of Orthopaedics and Traumatology, and dRadiology, Onze Lieve Vrouwe Gasthuis; bDepartment of Orthopaedics, University Medical Center Utrecht; and the cCentre for Statistical Consultation, University of Stellenbosch. Reprint requests: W. Jaap Willems, MD, PhD, Department of Orthopaedics and Traumatology, Onze Lieve Vrouwe Gasthuis, 1e Oosterparkstraat 279, 1091 HA Amsterdam, The Netherlands. (E-mail: [email protected]). Copyright © 2007 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2007/$32.00 doi:10.1016/j.jse.2007.02.115
This study used 8 formaldehyde-preserved scapulae and 6 fresh-frozen scapulae from skeletally mature individuals. Scapulae with a bony defect or erosion of the glenoid were excluded. A 3D CT scan (AVE 1 Philips Tomoscan, 125 mA, 120 kV, 1 second; field of view, 120 mm; filter, 1H; slice, 1 mm; table speed, 1 mm/s; reconstruction index, 1 mm; Philips Medical Systems, Best, The Netherlands) and an MRI scan (3D T1-weighted, fast field echo, echo planer imaging, Matrix 256*256, 0.5 mm slice thickness; echo time, 13.8 milliseconds; repetition time, 55; flip angle, 55) were made
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Figure 1 Digital photograph of sagittal view of a glenoid with created anterior defect. The missing part of the drawn circle (B) represents the size of the defect.
of each scapula. Reconstructions were made from 3D CT images, and the exact sagittal view of the glenoid was used for measurements. The volume MRI scan permitted obtaining the exact, most lateral sagittal view of the glenoid, which was used for measurements. The scapulae were cleared of soft tissue, including the labrum, and placed in a clamp. A digital photograph (Sony Digital camera, 1.3 megapixel, Sony, Japan) was made of the sagittal view of the glenoid with a caliper next to the surface to indicate its relative size. These predefect scans and photographs were used to confirm the circle shape of the inferior glenoid. With an electric saw, a defect was created at the anterior or anteroinferior aspect of the glenoid. The size and location of the defect were chosen randomly by one of the researchers. Again, a digital photograph and 3D CT and MRI scans were made. Sagittal views of the glenoid were used for analysis and measurements. The images were filed in a tagged image file (TIF) format and analyzed using OSIRIS 4.17 software (University of Geneva, Switzerland). The images were calibrated for their relative size. A circle was placed on the inferior part of the glenoid using the digital analysis software. The best fitting circle on
the inferior glenoid, according to the researchers, was used. The outer cortex of the inferior glenoid on the sagittal view was selected to be the landmark for circle placement. In a previous study, we demonstrated that the shape of the inferior part of the bony glenoid has the shape of a true circle.14 Therefore, when a circle was placed on the inferior part of the glenoid on the digital photograph and CT and MRI scan, the missing part of that circle should represent the size of the created defect. The surface of the circle and the surface of the missing part of that circle were measured (mm2). The size of the defect was calculated using the following formula, which was also used by Sugaya et al29: [(Surface B/Surface A) ⫻ 100%] (Figures 1, 2, and 3). All measurements were done by 2 independent researchers. Each measurement was repeated 3 times and the averages were used for statistical analysis.
Statistical analysis For analysis of the reliability and conformity of the findings of both researchers for the different imaging modalities, scatter plots were made, and the correlation coef-
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Figure 2 Sagittal view of a 3-dimensional computed tomography reconstruction of the same glenoid as in Figure 1. The missing part of the circle (B) represents the size of the glenoid defect.
ficient (r2) was calculated. To analyze the differences of the measurements between the two researchers and between the different imaging modalities, Bland-Altman plots were made, and mean differences, maximum differences, and standard deviations were calculated. Repeated measures analysis of variance was used to detect significant differences between the measurements of the 2 researchers and for the different imaging modalities. A 5% significance level (P ⬍ .05) was used as a guideline for detecting significant differences.
RESULTS The MRI and CT images showed no difference in quality or appearance between the fresh and embalmed scapulae. All specimens had an exact circleshaped inferior glenoid on the digital photograph and CT and MRI scans before the defect was created. The measurements of the size of the glenoid defect taken from the different imaging modalities by the 2 researchers were analyzed. Figures 4, A and B show Bland-Altman plots for the comparison of the measurements taken from the digital photograph and the measurements taken from the CT scans for researcher. The 95% confidence interval for the difference in glenoid defect size measurements taken from CT scans compared with the measurements taken from
the digital photographs was 4.11% for researcher 1 and 8.06% for researcher 2. The r2 was 0.97 for researcher 1 and 0.90 for researcher 2. None of the measurements of researcher 1 showed a difference of more than 4%. Only 2 of the 14 measurements done by researcher 2 showed a difference between the measurements of more than 5.5%. Figure 5, A and B show Bland-Altman plots for the comparison of the digital photograph measurements with the MRI measurements for each researcher. The difference between the measurements taken from the MRI scans and the measurements taken from the digital photographs demonstrates a 95% confidence interval of 6.51% for researcher 1 and 8.11% for researcher 2. Only 1 measurement done by researcher 1 showed a difference in the measured size of the glenoid defect of more than 4.5%. Of the 14 measurements done by researcher 2, 12 showed a difference of less than 6%. The correlation between these two image modalities showed a r2 of 0.93 for researcher 1 and 0.92 for researcher 2. An overview of the mean differences, maximum differences, and standard deviations for the comparison of the measurements taken from the different image modalities for each researcher is summarized
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Figure 3 A sagittal view magnetic resonance scan of same glenoid as in Figure 1. Area B represents the glenoid defect.
in Table I. When the measurements of the 2 researchers were compared, the interobserver reliability for the measurements of the size of the glenoid defect taken from the digital photographs showed an r2 of 0.97, with a standard deviation of 2.36%. The interobserver reliability for the CT scan measurements shows an r2 of 0.94. Only 1 defect measurement on a CT scan showed a difference of more than 3% between the 2 researchers. The r2 for the measurements done by the 2 researchers on the MRI scans was 0.87. Of the 14 MRI measurements, 11 showed a difference between the 2 researchers of less than 4.5%. The maximum difference in the measurement of the size of a glenoid defect on MRI between the 2 researchers was 10.77%. Table II gives an overview of the comparison of the measurements of the size of glenoid done by the 2 researchers for each image modality. Mean difference, maximum difference, standard deviation, and the r2 are noted. Paired t tests showed no statistical significant differences between the measurements done on the different image modalities for each researcher. No statistical differences were found between the measurements of the 2 researchers.
DISCUSSION Although it is well known that a defect or erosion from the anteroinferior glenoid rim is a common finding in glenohumeral instability,3,4,8,12,17,24,27,29,32 the exact role of this finding is still being discussed. Some authors found a relationship between the presence and size of a glenoid defect and redislocation after Bankart repair,3,4,16,22,23,31,33 but others could not confirm this relationship.13,20,24 Future prospective studies are needed to investigate this particular subject objectively in anterior glenohumeral instability. To perform such studies, a validated and generally accepted method for measuring the size of a glenoid defect is needed. Different ways to measure the size of a glenoid defect have been described in the literature. Bigliani3 described the size of the glenoid rim fracture as a percentage of the original width of the inferior glenoid. Ungersbock et al33 described the size of a glenoid defect in millimeters of the width of the defect. Gerber and Nyffeler10 showed a decrease in dislocation resistance of more than 30% if the glenoid rim lesion measured more than half of the maximal anteroposterior diameter of the glenoid fossa. This quan-
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Figure 4 Differences in measurements (%) of the glenoid defect on 3-dimensional computed tomography images (CT) compared with the “actual” size on the digital photograph (DP). A, Results for researcher 1. B, Results for researcher 2.
Figure 5 Differences in measurements (%) of the glenoid defect on magnetic resonance images (MRI) compared with the “actual” size on the digital photograph (DP). A, Results for researcher 1. B, Results for researcher 2.
tification method was used by Warner et al35 in a clinical study. Burkhart et al5 published a method for quantifying a glenoid defect arthroscopically with a special caliper. With this method, an arthroscopic caliper is placed in the center of the bare spot of the inferior glenoid. From this point, the distance to the posterior labrum and the anterior glenoid rim are measured and compared. The difference between these 2 distances in millimeters represents the size of the glenoid defect. Other studies mention bony Bankart lesions but do not give a quantification of the defect.22,32 Three studies on preoperative measurement of a glenoid defect have recently been published.12,15,29 Itoi et al16 showed in a cadaver study that a defect of 21% of the glenoid length requires bone grafting. To address the problem of defect measurement preoperatively, they published a study on quantification of the defect.15 CT scans and West point view radiographs were used to determine the size of a glenoid defect.
They found that a defect of 21% of the length of the glenoid appeared was 18.6% of the intact width on a West point view and 50% of the intact width of a slice of the lower one fourth on the CT image. The drawback of their study is that a standard osteotomy was made anteroinferiorly, and this does not address measurements for more anteriorly located defects. Second, with this method the measurements have to be compared with the normal width of the glenoid on the contralateral side. This can be a problem in patients with bilateral instability or congenital asymmetry of the scapulae. In 2003, Griffith et al12 published a study for measurement of a glenoid defect with CT. They concluded that the best indicator of glenoid bone loss was the width of the glenoid and the width-to-length ratio of the glenoid, but for this method, measurements also need to be compared with measurements from the contralateral shoulder. It is also difficult to measure the length of the glenoid accurately on a sagittal reconstruction because of the difficulty determining the exact top of the glenoid.
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Table I Differences between measurements taken from different image modalities Researcher 1 Digital photos CT MRI
Researcher 2
Average (%)
Max (%)
SD (%)
r
Average (%)
Max (%)
SD (%)
r2
⫺0.81 ⫺0.61
⫺3.98 6.86
2.10 3.32
0.97 0.93
⫺1.21 0.74
8.32 8.48
4.11 4.14
0.90 0.92
2
SD, Standard deviation; r2, correlation coefficient; CT, computed tomography; MRI, magnetic resonance images.
Table II Differences for measurements of the glenoid defect between the two researchers for each image modality Images
Average differences (%)
Max difference (%)
SD (%)
r2
CT-CT MRI-MRI DIG-DIG
0.48 2.22 0.87
8.03 10.77 5.25
2.89 4.39 2.36
0.94 0.87 0.97
SD, Standard deviation; r2, correlation coefficient; CT, computed tomography; MRI, magnetic resonance imaging; DIG, digital photographs.
Sugaya et al29 described a method to measure a defect preoperatively on 3D CT images. They found a bony fragment or an erosion of the anterior glenoid rim in 90% of their patients. To use this method, it is not necessary to know the size of the original glenoid because the drawn circle on a sagittal view of the glenoid will point out the original contour of the glenoid. This can be important for patients with bilateral shoulder instability. The method described by Sugaya29 was not validated for reliability.34 In our cadaveric study, we tried to validate this circle method with 2 independent researchers. To our knowledge, no previous studies have tried to quantify a glenoid bone defect with MRI. MRI arthrography is the modality of choice in anterior glenohumeral instability, especially for showing abnormalities of the capsulolabral complex.1,7,25,28 Only a few studies mention the ability to detect bony abnormalities of the glenoid with MRI.28,36 The limitation of this study is the lack of a true gold standard that represents the actual size of the glenoid defect. To our knowledge, there is no generally accepted method of measuring the exact size of a glenoid defect. In our study design, the measurements from the digital images were the gold standard. The measurements from the digital images showed the highest correlation coefficient (r2 ⫽ 0.97) between the 2 researchers. Comparing the measurements for both researchers with the digital images, the measurements done with the CT scan showed smaller differences for researcher 1 (standard deviation, 2.10) compared with researcher 2 (standard deviation, 4.11). The differences between the MRI and the digital images were approximately the same for both re-
searchers. The CT measurements show a higher correlation between the 2 researchers than the MRI measurements. Although the differences in measurements between the 2 researchers were as high as 8.03% for the CT measurements and 10.77% for the MRI measurements, most of the differences in measurements were less than 3% for the CT and less than 4.5% for the MRI measurements. These differences in measurements can be explained by the interpretation of the borders of the glenoid rim on images from CT and MRI and the positioning of the circles by the researchers, which can be subject to discussion. We used volume MRI scans, which allowed us to select the exact sagittal view from the most lateral part of the glenoid bone. This maybe difficult in a clinical setting and therefore can be a potential source of errors. Taking the results of our study into account, claims from previous studies3,4,16,33 about the exact cutoff size of a glenoid defect as an indication for the need of a bony procedure (ie, Latarjet) are difficult for practical use. One must be aware of the error in measurements of a glenoid defect. Other limitations of this study are the limited number of investigated glenoids and the 2D measurements of the 3D surface of the glenoid. In our opinion, this last point is not very relevant because the bony surface of the glenoid is relatively flat and the radius of the glenoid socket is predominantly formed by the overlying cartilage.26 Another limitation is that we did not compare the different described quantification methods10,12,16 with the method described by Sugaya.29 Advantages of the circle method are its simplicity and that the size of the glenoid defect can be determined preoperatively without using the contralateral shoulder. Measurement of a glenoid defect with the circle method can easily be included in the radiologic protocol for CT or MRI scanning. This method is not restricted by the size or the location of a glenoid defect and can be used with CT as well as MRI. MRI can be the image modality of choice when soft-tissue structures need to be assessed as well as bony abnormalities. Measurements done with the circle method will give a good preoperative estimation of the amount of
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bone loss and can be used in future studies on the effect of bone loss of the anteroinferior glenoid in shoulder instability. We thank W. van Wolveren and S. Klomp, Department of Anatomy University of Utrecht, The Netherlands, for their help and assistance with the preparation of the cadaver specimen. We also would like to thank S. Phieltjens, Department of Radiology, Onze Lieve Vrouwe Gasthuis, Amsterdam, for his help with the making and processing of the CT and MRI scans. REFERENCES
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