Standard vs. the alternative centerline technique for baseplate fixation in reverse shoulder arthroplasty: a comparison of anterior shoulder pain

Reverse total shoulder arthroplasty (rTSA) has increasingly become a reliable intervention to improve function and pain for a variety of indications. Glenoid fixation is critical to the success of rTSA, and traditionally the standard anatomic centerline is used, allowing for central baseplate fixation. However, in cases of severe bone loss, baseplate fixation along the alternative centerline has been described. The baseplate axis is anteverted and inferiorly tilted, allowing for fixation into a column of bone where the base of the scapular spine and coracoid meet, thereby prioritizing glenoid fixation. Previous studies have demonstrated no differences in pain, function, or complications when comparing the former technique to standard centerline fixation. However, there is concern that excessive anteversion may lead to pain related to anterior soft tissue or bony impingement. Therefore, the objective of this study was to investigate the outcomes of rTSA in cases when the alternative centerline was used for baseplate fixation and to specifically assess the incidence of anterior shoulder pain and dysfunction. This was a single-institution retrospective series of all primary or revision rTSA patients who underwent glenoid baseplate fixation using an alternative centerline with a minimum 2-year follow-up. A matched-cohort analysis was performed to compare the standard and alternative centerline groups (ratio 2:1) based on indication for surgery, age, and sex. Our primary outcome was anterior shoulder pain using the Anterior Shoulder Pain and Dysfunction Survey. Secondary outcomes included the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score (ASES), visual analog pain scale (VAS), Single Assessment Numeric Evaluation (SANE), radiographic outcomes, and complications. A total of 48 patients participated in our matched analysis (16 alternative centerline group and 32 in the standard centerline group). The mean age of our cohort was 65.4 ± 9.3 years, of which 28% were males. The average length of follow-up was 62.6 ± 37 months. Sixty-three percent and 70% of alternative and matched cases, respectively, were revisions. At final follow-up, anterior shoulder pain and dysfunction was not significantly different between groups (28.1 ± 9.2 vs. 28.2 ± 7.0, P = .96). Furthermore, ASES, VAS, and SANE scores did not differ significantly between groups postoperatively at final follow-up. Three patients in the alternative centerline group (18%) developed radiographic evidence of humeral loosening. Four patients developed notching (25%), and 1 patient had an instability episode (6%). There were no cases of baseplate failure or acromial stress fractures in the alternative centerline group. Postoperative reverse shoulder angle (inferior tilt) was significantly larger in patients treated with an alternative centerline (-37° ± 11° vs. -14° ± 6°, P = .03). In the control group, there was 1 patient with an acromial stress fracture, 1 with baseplate failure, and 1 with low-grade notching. In cases of severe bone loss, baseplate fixation along the alternative centerline is a reasonable option with low complication rates. Although there is increased baseplate anteversion with this technique, our investigation did not demonstrate an increase in anterior shoulder pain and dysfunction with similar postoperative outcomes as the standard centerline technique following rTSA.