Diagnostic Accuracy of MRI in the Measurement of Glenoid Bone Loss

Transcription

1 Musculoskeletal Imaging Original Research Gyftopoulos et al. MRI of Glenoid one Loss Musculoskeletal Imaging Original Research Soterios Gyftopoulos 1 Saqib Hasan 2 Jenny encardino 1 Jason Mayo 1 Samir Nayyar 2 James abb 1 Laith Jazrawi 2 Gyftopoulos S, Hasan S, encardino J, et al. Keywords: circle method, glenoid bone loss DOI: /JR Received ugust 3, 2011; accepted after revision December 26, Department of Radiology, New York University Hospital for Joint Diseases, 301 East 17th St, New York, NY ddress correspondence to S. Gyftopoulos (Soterios20@gmail.com). 2 Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, NY. JR 2012; 199: X/12/ merican Roentgen Ray Society Diagnostic ccuracy of MRI in the Measurement of Glenoid one Loss OJECTIVE. The purpose of this study is to assess the accuracy of MRI quantification of glenoid bone loss and to compare the diagnostic accuracy of MRI to CT in the measurement of glenoid bone loss. Materials and Methods. MRI, CT, and 3D CT examinations of 18 cadaveric glenoids were obtained after the creation of defects along the anterior and anteroinferior glenoid. The defects were measured by three readers separately and blindly using the circle method. These measurements were compared with measurements made on digital photographic images of the cadaveric glenoids. Paired sample Student t tests were used to compare the imaging modalities. Concordance correlation coefficients were also calculated to measure interobserver agreement. RESULTS. Our data show that MRI could be used to accurately measure glenoid bone loss with a small margin of error (mean, 3.44%; range, %) in estimated percentage loss. MRI accuracy was similar to that of both CT and 3D CT for glenoid loss measurements in our study for the readers familiar with the circle method, with 1.3% as the maximum expected difference in accuracy of the percentage bone loss between the different modalities (95% confidence). CONCLUSION. Glenoid bone loss can be accurately measured on MRI using the circle method. The MRI quantification of glenoid bone loss compares favorably to measurements obtained using 3D CT and CT. The accuracy of the measurements correlates with the level of training, and a learning curve is expected before mastering this technique. T he glenohumeral joint provides the greatest range of motion when compared with the remainder of the large joints in the body. Several structures, both dynamic and static, play important roles [1, 2]. The glenoid, a static restraint, helps contain the humeral head in the midrange of motion when the capsular structures are lax. The containment is a result of the shape and size of the glenoid articular surface. ny compromise in the shape or size of the glenoid articular surface will decrease the resistance to the humeral head and increase the forces on the adjacent labroligamentous structures, leading to instability [2 4]. Glenoid bone loss is a common finding in anterior shoulder dislocation, with a reported prevalence of up to 90% in the setting of recurrent dislocation [5]. There are two main types of glenoid bone loss lesions: osseous ankart and glenoid compression deformity or erosion. The osseous ankart lesion is a displaced fracture fragment that is located adjacent to, but separate from, the remainder of the glenoid. compression lesion appears as flattening of the anterior margin of the glenoid. The importance of glenoid bone loss is its ability to predispose to shoulder dislocation, when large enough, in patients with both chronic anterior instability and prior labroligamentous repair. Several previous studies have investigated the critical amount of glenoid bone loss thought to predispose to recurrent dislocation [6 8]. The definition of a large or significant amount of bone loss varies, with estimates of 20 30% of the glenoid width and greater than 21% of the glenoid length [6 8]. Glenoid bone loss can be measured directly in the operating room, but there is no consensus as to the best method [9]. lthough intraoperative estimation of glenoid bone loss is useful, the ability to form an accurate estimate of this loss before surgery is advantageous for surgical planning and patient counseling, because it provides the surgeon the opportunity to discuss all the possible options and outcomes in a more complete fashion. JR:199, October

2 Gyftopoulos et al. Various imaging modalities have been used to estimate glenoid bone loss, with 3D CT currently considered the reference standard [10 17]. On the basis of the principle that the inferior glenoid has a consistent circular shape, a measuring technique called the circle method has been developed and used to accurately estimate the margins of the glenoid and associated bone loss on 3D CT [5, 18]. MRI is the preferred imaging modality for the diagnosis of soft-tissue injuries that result from shoulder dislocation, especially injury to the labroligamentous complex [19 23]. The evaluation of both soft-tissue injuries and glenoid deficiency on a single imaging study would be of great value to both the patient and the referring clinician by limiting the time and cost of the preoperative workup. Furthermore, there would be less need for a CT scan and its associated radiation exposure. The accuracy of MRI measurements of glenoid bone loss using the circle method has been addressed only once before in the literature, to our knowledge [24]. The aim of our study is to test the accuracy of MRI for the quantitative assessment of glenoid bone loss as compared with CT. Our hypothesis is that MRI can quantify glenoid bone loss as accurately as CT and 3D CT using the circle method. Materials and Methods Institutional review board approval was not needed for this study. Cadavers and Specimen Preparation Eighteen shoulders from fresh-frozen cadavers (11 men and 7 women; age range, years; mean age, 55 years) were used for the study. The specimens were frozen at 9 C and thawed overnight at room temperature for the experiment. The soft tissues and humerus were removed and discarded, producing a completely bare glenoid in each specimen. Each specimen was prepared in the same manner and numbered None of the specimens had preexisting anterior bone loss; therefore, all 18 bare glenoids were included in our study. Osteotomy custom clamp was assembled to secure each individual scapula and a separate measuring ruler (Figs. 1 and 1). tripod (Modo Tripod, Manfrotto) and 15.1-megapixel digital single-lens reflex camera (EOS Digital Rebel T1i, Canon) were set up approximately 7 feet (2.1 m) from the clamped specimens allowing an en face (sagittal) view of the glenoid surface. 100-mm 1:1 aspect ratio macro lens (EF Macro USM, Canon) was used to ensure minimal distortion of images. bone saw was used to create a straight cut along the anterior and anteroinferior margin of the glenoid at a predetermined distance from the glenoid bare spot (Fig. 1). Images of the sagittal view of the glenoid were obtained before and after the osteotomy. Images were processed using photo-editing software (Photoshop, dobe). MRI and CT Each specimen underwent CT (SOMTOM Sensation 40, Siemens Healthcare) and MRI (MGNETOM Verio 3 T, Siemens Healthcare) examinations. The CT protocol consisted of 3-mm axial images of the glenoid reconstructed into 1-mm sagittal and coronal 2D reconstructions using the following parameters: 120 kv, 280 m, and pitch of 0.9. The CT data were also used to produce a 3D reconstruction of each glenoid. The MRI protocol consisted of coronal, axial, and sagittal T1-weighted (TR/TE, 781/9.5) sequences of the glenoid acquired using a 15-channel transmitreceive phased-array knee coil using the following parameters: FOV of cm, matrix of , bandwidth of 369 Hz/pixel, acquisition time of 3 minutes 23 seconds, and a slice thickness of 2 mm (interslice gap, 0%). T1 weighting was selected because it was thought to most accurately represent osseous detail. Using the circle method technique and Isite software (Philips Healthcare), three readers analyzed the data separately and blindly. Reader 1 (with 2 years of musculoskeletal radiology experience) was familiar with the circle method technique and had been using it in his MRI and CT interpretations for nearly 9 months with surgical correlation. Reader 2 (with 1 year of musculoskeletal radiology experience) had been trained by reader 1 to use this technique over the course of 6 months before this study and had used it in all of his MRI and CT interpretations under the supervision of reader 1. Reader 3 (with 14 years of musculoskeletal radiology experience) had never used this technique before and had only reviewed a 15-minute tutorial organized by reader 1 explaining the circle technique immediately before performing the measurements. Measurements Each reader measured the size of the glenoid defect using a sagittal image tangential to the articular surface of the glenoid on CT and MRI and using a sagittal view of the glenoid on the 3D reconstructions (Figs. 2 2C). For each image, a vertical line bisecting the glenoid along its long axis was drawn from the supraglenoid tubercle (Fig. 3). Next, a best-fit circle was placed along the inferior portion of the glenoid, ensuring that the center of the circle overlaid the vertical line (Fig. 3). The glenoid defects were measured in terms of width (millimeters) and percentage bone loss in the anteroposterior dimension, calculated Fig year-old male cadaver., Digital image obtained before osteotomy shows cadaveric glenoid held in place by custom clamp with ruler along its inferior aspect., Digital image after osteotomy shows defect along anterior margin of glenoid. 874 JR:199, October 2012

3 MRI of Glenoid one Loss as 1 [(width of glenoid width of defect) / width of glenoid] (Figure 3C). The width and percentage bone loss were measured in the anteroposterior dimension because we thought that these parameters were simpler, more accurate, and more reproducible [6, 17] (Figs. 4 and 4). Digital images of the glenoid with the superimposed circle were captured and stored (5 Clicks, Interapple) for later analysis of each reader s technique. The glenoid defects on the postosteotomy digital photographic images were measured using the same technique and OsiriX software (version 3.61, OsiriX Foundation). Reader 1 obtained a second set of measurements, blindly, 4 weeks after the initial measurements. Reader 3 conducted a repeat set of measurements 3 months after the initial session. Statistical nalysis paired-sample Student t test was used to compare imaging modalities in terms of the errors in the measurements derived by each individual reader. The error in each imaging measurement relative to the measurement obtained on the digital photograph of each cadaveric specimen (i.e., the reference standard) was represented as the absolute value of the difference between the imaging measure and the reference standard assessment for the same specimen. The percentage error of each measurement was also stratified by the reference standard size of the deficit. 95% CI was calculated for the true mean difference between modalities in terms of the error in the measured size Fig year-old male cadaver (same as in Fig. 1). C, Representative images used for measurement were obtained with 3D CT (a), CT (), and sagittal T1-weighted MRI (TR/TE, 781/9.5) (C). and percentage of deficit derived by each reader. concordance correlation coefficient was calculated between the measures provided by different readers using the same modality. concordance correlation coefficient was also calculated between the replicate measures performed by reader 1 at times separated by 4 weeks. Results The average percentages and lengths of the glenoid defects measured on the digital images of the cadavers (i.e., the reference standards) were 25.3% (range, 9 42%) and 7.04 mm (range, mm), respectively. The mean (± SD) of the differences (error) between the percentages of glenoid bone loss estimated by the readers on imaging compared with the reference standard measurements are summarized in Table 1. The differences for the MRI measurements were 2.06% ± 2.41% (reader 1), 2.33% ± 1.41% (reader 2), and 5.94% ± 3.64% (reader 3). The 3D CT measurements were 2.22% ± 2.37% (reader 1), 2.17% ± 1.54% (reader 2), and 3.50% ± 3.28% (reader 3). The CT measurements were 2.56% ± 2.85% (reader 1), 2.22% ± 1.66% (reader 2), and 17.11% ± 23.52% (reader 3). The differences in length for MRI measurements were 0.78 ± 0.69 mm (reader 1), 0.58 ± 0.45 mm (reader 2), and 2.27 ± 1.32 mm (reader 3); those for the 3D CT measurements were 0.86 ± 0.73 mm (reader 1), 0.70 ± 0.40 mm (reader 2), and 1.43 ± 1.20 mm (reader 3); and those for CT measurements were 0.87 ± 0.87 mm (reader 1), 0.84 ± 0.61 mm (reader 2), and 2.31 ± 1.53 mm (reader 3). If MRI was used to measure the glenoid defect instead of 3D CT, the maximum change in accuracy expected in terms of percentage was 0.5% to 0.8% (reader 1), 1.1% to 0.7% (reader 2), and 3.8% to 1.1% (reader 3) with 95% confidence. Similarly, the maximum change in accuracy expected in terms of length of the glenoid bone loss was 0.16 to 0.24 mm (reader 1), 0.21 to 0.37 mm (reader 2), and 1.27 to 0.26 mm (reader 3). When stratified by the size of the glenoid bone loss (< 20%, 20 29%, and 30%), the differences (error) between the reference standards and the measurements calculated on imaging, across all three size categories, were % for MRI and % for 3D CT (reader 1), % for MRI and % for 3D CT (reader 2), and % for MRI and % for 3D CT (reader 3) (Table 2). These data, however, were not found to be statistically significant because of the low number of cadavers used. Interreader agreement was substantial for readers 1 and 2 for all the modalities ( ). Interreader agreement for readers 1 and 3 and for readers 2 and 3 was moderate for 3D CT and MRI ( ), but substantially lower for CT ( 0.28) (Table 3). Intrareader C JR:199, October

4 Gyftopoulos et al. agreement was substantial for all modalities (0.95) (Table 4). Reader 3 obtained another set of measurements 3 months after the initial session after multiple training sessions with reader 1. The difference between the CT measurements and the reference standard was 5.09% ± 3.39%, whereas the difference for MRI was 4.46% ± 4.23%. There was moderate interobserver agreement for all the measurements. Discussion To the best of our knowledge, accurate MRI estimation of glenoid bone loss has been reported in only one previous study. Huijsmans et al. [24] showed that the circle method could be used on MRI and CT to produce good estimates of the amount of glenoid bone loss. Our study had similar findings. Our study indicates that MRI, CT, and 3D CT can be used to accurately measure glenoid bone loss. Furthermore, our study is the first, to our knowledge, to show that the accuracy of glenoid bone loss quantification using the circle Fig year-old female cadaver. C, Sequential steps of circle method used for glenoid bone loss measurement on sagittal T1-weighted MRI (TR/TE, 781/9.5) are illustrated. Line is drawn along long axis of glenoid (). est-fit circle is formed along inferior aspect of glenoid (). Glenoid bone loss is measured by calculating difference between anterior margin of circle (estimate of anterior margin of normal glenoid) and margin of remnant glenoid (green line) (C). lue line (C) represents expected diameter of normal glenoid and is used to calculate percentage loss. Fig year-old male cadaver. and, Small (~ 15%) glenoid bone defect was measured on MR image () and 3D CT image () of cadaveric shoulder specimen using circle method. Red line indicates long axis of glenoid, yellow circle is best-fit circle, blue line represents expected diameter of normal glenoid and is used to calculate percentage loss, and green line shows amount of bone loss. method depends greatly on the level of familiarity of the interpreting radiologist with this technique. On the basis of our data, MRI has a small margin of error in estimated percentage loss, with a mean of 3.44% (range, %). MRI accuracy was similar to that of both CT and 3D CT for glenoid measurement in our study for our readers familiar with the circle technique, with the maximum expected difference in accuracy of the percentage bone loss if MRI was used instead of 3D CT being 1.3% with 95% confidence. lthough not statistically significant, our data also suggest that glenoid bone loss can be ac- C 876 JR:199, October 2012

5 MRI of Glenoid one Loss TLE 1: Measured Glenoid one Loss and Error in the Measured Percentage When Compared With the Reference Standard by Each Reader Using Each Modality Reader, Modality Measured (%) Error (%) Reader 1 CT ± ± D CT ± ± 2.37 MRI ± ± 2.41 Reader 2 CT ± ± D CT ± ± 1.54 MRI ± ± 1.41 Reader 3 CT ± ± D CT ± ± 3.28 MRI ± ± 3.64 Note Data are mean ± SD. Reference standard is 25.28% ± 9.16%. curately measured throughout a wide range of sizes using all three modalities for our readers familiar with the circle technique. The data revealed moderate-to-substantial reproducibility among the measurements of all the readers, except when comparing the CT values of readers 1 and 3 and readers 2 and 3. Intraobserver reproducibility was substantial as well. The measurements did vary among the three readers, especially for the MRI and CT measurements between reader 3 and the other two readers. lthough readers 1 and 2 had been using this method on a regular basis in their clinical CT and MRI cases with surgical correlation of their measurements, reader 3 had no previous training or exposure to the technique before enrolling as a reader. We therefore attribute the discrepancy in measurements to the lack of preparatory training of reader 3 with the circle method before the study. Reader 3 conducted another set of measurements of the glenoid bone loss using the CT and MRI data 3 months after the initial session and multiple training sessions with reader 1. The margin of error for the CT (initial measurements were 17.1%, compared with 5.1% for the second set) and MRI measurements ( %) decreased, showing TLE 2: Error in the Measured Percentage of Glenoid one Loss Derived by Each Reader Using Each Modality, Stratified by the Reference Standard Size of the Deficit Reader, Size (%) CT 3D CT MRI Reader 1 < ± ± ± ± ± ± ± ± ± 3.3 Reader 2 < ± ± ± ± ± ± ± ± ± 1.7 Reader 3 < ± ± ± ± ± ± ± ± ± 4.2 Note Data are mean ± SD. improved accuracy with increased familiarity with the circle method. In theory, the implementation of the best circle method should be simple given the fact that the shape of the inferior glenoid conforms to a circle. In actuality, this is not the case. It can be difficult to determine the exact size of the circle. To help correct for this, we added an initial step of extending across the glenoid a line perpendicular to the midpoint of the supraglenoid tubercle. This is a useful addition to previously described applications of the circle method. lthough this extra step did not guarantee accurate sizing of the bestfit circle, it did provide a highly reproducible means to ensure consistent placement of the center of each best-fit circle. We think that this also provides a straightforward reference for instructing future readers in using the circle method with any modality. With regard to the actual circle size, review of the stored CT and MR images of the glenoid with a superimposed circle recorded at the time of measurement showed that the most common error was in underestimating the size of the glenoid. lthough this was mostly a technical error related to implementation of the circle method, the lack of surrounding soft tissues in the cadaveric specimen scans likely contributed to the difficulty of forming the circles, because markers for the margins of the glenoid, such as the labrum and capsule, were absent. On the basis of our results, we recommend that the radiologist planning on using the circle method fully understand and become familiar with its steps before incorporating these measurements into his or her reports. Practicing this technique on studies with surgically confirmed glenoid defects and percentages would also be helpful. It is important to note that the most accurate initial measurements for reader 3 were made on the 3D CT images, suggesting that this modality may be the easiest to use for the radiologist who is first exposed to the circle method. The importance of our results lies in the ability of MRI to provide treatment-guiding information in a single diagnostic examination. MRI is already considered the preferred imaging modality for the evaluation of softtissue injury related to shoulder dislocation. MRI also provides fundamental information related to osseous injuries, such as the presence of Hill-Sachs and glenoid fractures. t our institution, CT and 3D CT are frequently performed, in addition to MRI, for further characterization of these osseous findings and JR:199, October

6 Gyftopoulos et al. TLE 3: Concordance Correlation Coefficient etween the Measurements Provided by Different Readers Using the Same Modality Readers Compared Modality Readers 2 and 3 Readers 1 and 3 Readers 1 and 2 CT D CT MRI Note The concordance correlation coefficient is a measure of interreader agreement (reproducibility) and would be interpreted as an indication of substantial agreement when it is 0.9. TLE 4: Concordance Correlation Coefficient etween the Replicate Measurements Provided by Reader 1 at Times Separated by 4 Weeks Modality Deficit Percentage CT D CT MRI Note The concordance correlation coefficient is a measure of interreader agreement (reproducibility) and would be interpreted as an indication of substantial agreement when it is 0.9. are considered the imaging reference standard for determining the amount of glenoid bone loss. However, our results suggest that MRI can also be used to reliably quantify the amount of glenoid bone loss. This would eliminate the need for an additional CT examination and its associated cost and radiation dose. Our study has several limitations. The first is the use of the measurements obtained on the digital photographic images as the reference standard. lthough the circle method has been confirmed as a reliable means to measure glenoid bone loss on imaging, this technique cannot be implemented in the operating room by our surgeons and thus does not simulate normal clinical conditions. Second, the use of bare cadaveric glenoids for measurement without adjacent soft-tissue structures does not simulate normal imaging anatomy. We think that this, as mentioned earlier, increased the level of difficulty of measuring the defects. The inability to demarcate the bare area on imaging on a consistent basis also may have decreased the accuracy of the measurements. Finally, the lack of training with the circle method was likely the main reason for the larger margin of error in the initial measurements obtained by reader 3. In conclusion, we think that glenoid bone loss can be accurately measured on MRI by readers familiar with the circle method. The MRI quantification of glenoid bone loss compares favorably to measurements obtained using 3D CT and CT. The accuracy of the measurements correlates with the level of training, and a learning curve is expected before mastering this technique. References 1. igliani LU, Kelkar R, Flatow EL, Pollock RG, Mow VC. Glenohumeral stability: biomechanical properties of passive and active stabilizers. Clin Orthop Relat Res 1996; 330: bboud J, Soslowsky LJ. Interplay of the static and dynamic restraints in glenohumeral instability. Clin Orthop Relat Res 2002; 400: urkhart SS, De eer JF. 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