Differences in Measurement of Glenoid Morphology Between Radiographs and Computed Tomography

Background: Reverse shoulder arthroplasty (RSA) requires deliberate preoperative planning and evaluation of glenoid deformity. The shoulder β and RSA angles, as described by Mauer and Boileau, respectively, are of value for preoperative planning for RSA. Purposes: To evaluate differences in relevant glenoid markers, such as the β and RSA angles, between plain radiographs and computed tomography (CT) scans and to further introduce and evaluate a novel measurement, the inferior glenoid bony resection depth (BRD), which is the resection distance required for placement of a baseplate in 0° of superior inclination. Study Design: Cohort study (Diagnosis); Level of evidence, 3. Methods: Patients with both plain radiographs and CT scans of the shoulder performed at the same institution within 3 months were reviewed. The shoulder β and RSA angles and BRD were assessed using radiographs and 2-dimensional CT scans. All radiographic measures were compared based on imaging modality (radiographs vs 2-dimensional CT scan). A subgroup analysis was conducted to evaluate differences between male and female patients. Results: In total, 41 patients were included. The mean β angle on radiographs was greater than when measured using CT (78.8° vs 76.9°, P = .02). The average resection depth was higher on radiographs as well (7.32 mm vs 5.86 mm, P < .001). Furthermore, men had a higher average β angle than women (81.6° vs 75.8°, P = .001). Conclusion: Plain radiographs may overestimate shoulder β angle and inferior glenoid resection. In addition, inferior glenoid resection depth necessary to achieve a neutral baseplate, as measured on both radiograph and CT, would lead to overresection of the glenoid, putting patients at risk for implant subsidence. We further found that there may be differences in glenoid inclination based on patient sex.