Arthroscopic investigation revealed a Bankart lesion, evidence of injury to the anteroinferior portion of the labrum, in ninety-seven of the 100 shoulders. The glenoid morphology in the remaining three shoulders had been classified as normal preoperatively with use of the three-dimensionally reconstructed computed tomography. An osseous fragment was observed in forty-five of the fifty shoulders that had been classified as having an osseous Bankart lesion on the three-dimensionally reconstructed computed tomography scan. Arthroscopic visualization of the osseous fragment was not possible initially since each fragment was covered by or embedded in the surrounding soft tissue. Only after separation of the labroligamentous complex from the glenoid neck during preparation did the fragments become visible. The five fragments that had been detected preoperatively but were not seen arthroscopically had been classified as small (average percentage of the glenoid rim, 2.3%). In the shoulders that had been seen to have a distinctly abnormal morphology on three-dimensionally reconstructed computed tomography, regardless of the presence of an osseous fragment, the arthroscopic appearance of the anteroinferior portion of the glenoid rim was compatible with the appearance demonstrated by the three-dimensionally reconstructed computed tomography. However, small morphologic changes of the glenoid rim observed with three-dimensionally reconstructed computed tomography were not identifiable with arthroscopy.
Conventional radiography is widely used to detect osseous abnormalities in patients who have glenohumeral instability, and a variety of specialized views have been developed 11. However, although conventional radiography is simple and useful for the majority of shoulders, it is not always reliable for detecting abnormalities of the glenoid in patients with traumatic glenohumeral instability 3. Stevens et al. showed the superiority of computed tomography scans, including three-dimensionally reconstructed images, over conventional plain radiographs for detecting osseous abnormalities, especially of the glenoid 11. We have been able to detect only large or distinct osseous defects, or fragments, of the glenoid on radiographs. Therefore, we believe that plain radiography is neither adequate for quantification of glenoid defects nor reliable for surgical planning because it does not provide detailed information about the glenoid rim.
According to previous reports, the prevalence of lesions of the glenoid rim in shoulders with traumatic anterior glenohumeral instability is quite variable 3,6-8. It is our belief that this apparent variability results from a limitation in the ability to detect abnormal morphology of the glenoid rim with ordinary imaging techniques such as plain radiography 7, plain computed tomography 9,11, computed tomography-arthrography 3,10, and even direct visualization during surgery 3,6. We have found that three-dimensionally reconstructed computed tomography with the humeral head eliminated is a more reliable, noninvasive way to detect the morphology of the glenoid rim in patients with traumatic anterior glenohumeral instability. Moreover, the information obtained with this modality may be even more accurate than information obtained arthroscopically because, in the majority of shoulders, the glenoid neck is covered by soft tissue and scar tissue, limiting visualization of this area during arthroscopy. Edelson investigated 500 skeletons of mature individuals, without access to their medical history, and found that twenty-seven had a fracture of the glenoid rim 13. This suggests that the prevalence of glenoid rim lesions may be higher than has been reported in clinical studies 3,6-8. Bigliani et al. first proposed the term glenoid rim lesions in 1998 3. However, the prevalence of such lesions, which they identified at the time of open surgery, was only 11% in their series of 200 patients.
In the present study, the prevalence of glenoid rim lesions was 90%, with an osseous Bankart lesion in 50% of the glenoids and 40% of the glenoids showing an anomalous configuration. It is true that we had difficulty in distinguishing a small osseous fragment from an erosion in some shoulders. It is possible that erosion is a small marginal fracture that has smoothed out. However, clinically these differences have no effect on surgical planning. We believe that the most important information derived from this study is that 90% of the glenoid rims had morphologic changes, a fact that may influence surgical decision-making and outcomes 14-16.
Quantitative evaluation of the morphology of the glenoid rim is difficult with the use of ordinary imaging techniques or simple visualization since osseous fragments are often covered by soft tissue. After studying normal healthy glenoids on en face three-dimensionally reconstructed computed tomography images with the humeral head eliminated, we realized that the inferior portion of the pear-shaped glenoid contour can be approximated to a true circle. Our method of quantifying the glenoid bone defect is simple but not completely accurate as it depends on manual work to some extent. However, we believe that it is more accurate than other imaging methods and that it is simple and practical enough for clinical use. We believe that definition of glenoid morphology prior to surgery is important in terms of surgical decision-making. On the basis of previous work 4, we think that when a patient has a large osseous Bankart lesion, as defined with our classification system, bone-grafting should be one of the treatment options. For shoulders with a medium or small osseous Bankart lesion, our first choice is arthroscopic reconstruction with fixation of the osseous fragment to restore glenoid morphology 16-18. Thus we believe that evaluation of the glenoid morphology and quantification of the size of the defect with three-dimensionally reconstructed computed tomography provides useful information for preoperative decision-making and may contribute to better surgical outcomes.
Investigation performed at Funabashi Orthopaedic Sports Medicine Center, Funabashi, Chiba, and the Department of Orthopaedic Surgery, Kawatetsu Chiba Hospital, Chiba, Japan
The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
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