Glenoid baseplate migration with subsequent stabilization after reverse shoulder arthroplasty using a through-growth cage: a matched cohort study.

Few studies have evaluated the outcomes of glenoid baseplate migration after reverse shoulder arthroplasty (RSA). The question is whether an ingrowth central cage implant that has undergone early migration can restabilize due to cage ingrowth. The primary purpose of this study is to evaluate the radiographic factors associated with glenoid baseplate migration after RSA using a through-growth cage implant and secondarily evaluate their clinical outcomes with nonoperative management. A retrospective review of a single institution database was performed from January 1,2008 to June 30, 2017 for all shoulders using a single implant system (Equinoxe, Exactech, Inc., Gainesville, FL, USA). All RSAs with a documented complication of glenoid loosening were evaluated. Chart and radiograph review was performed to identify shoulders with confirmed glenoid loosening undergoing revision (revision group, n = 10) and those with migration that stabilized over time and avoided revision surgery (stable migration group, n = 10). The stable migration group was matched to an age-, sex-, and follow-up matched control group (1:3) (control group, n = 30). Demographic factors, preoperative and immediate postoperative radiographic factors, active range of motion (ROM), and patient-reported outcomes (PROMs) were compared. Radiographic factors evaluated included preoperative alpha/beta angles, humeral lengthening, glenosphere overhang, prosthesis-scapular neck angle, glenosphere inclination, and postoperative alpha/beta angles. A total of 50 RSA patients were evaluated at a mean follow-up of 38 months. Immediate postoperative inferior glenoid overhang was significantly less in the stable migration group compared to the control group (6.2 vs. 8.6 mm, P =.03). Preoperative ROM and PROMs were similar amongst all 3 groups. The stable migration group demonstrated improved ROM and PROMs compared preoperatively with all ROM and PROM values exceeding the minimally clinically important difference (MCID). The control group demonstrated greater improvements in ROM and PROMs compared to the stable migration group, with a majority exceeding the MCID. When compared to the revision group, the stable migration group had significantly greater improvements in forward flexion, ASES score, and Constant score as well as improvements above the MCID in abduction, external rotation, and SST score. RSA patients with glenoid migration and secondary stabilization still achieve improved ROM above the MCID, but the results are inferior to those RSA patients without glenoid migration. Approximately half of the shoulders with baseplate loosening using a through-growth cage implant will restabilize and have better ROM and function compared to those that are ultimately revised. Level III; Treatment Study [ABSTRACT FROM AUTHOR]