Prevalence and risk factors for stem subsidence following reverse shoulder arthroplasty using on-lay press-fit short stems

Introduction: In reverse shoulder arthroplasty (RSA), press-fit short stems offer benefits such as reduced operative time and bone preservation. However, stem subsidence has been reported, although the risk factors remain unclear. This study aimed to determine the prevalence and risk factors for stem subsidence in RSA with on-lay press-fit short stems, hypothesizing that a lower filling ratio (FR) would correlate with subsidence. Materials and Methods: This retrospective analysis included patients who underwent RSA using on-lay press-fit short stems between 2017 and 2023, with a minimum follow-up of 2 years. Subsidence was defined as a ≥5 mm reduction in the distance from the tip of the greater tuberosity to the distal end of the stem on anteroposterior radiographs between the immediate postoperative and final follow-up evaluations. FR was assessed at the metaphyseal (FRmet) and diaphyseal (FRdia) levels. Neutral alignment was defined as a stem–shaft angle within 5°. Clinical outcomes included range of motion, Constant score, and American Shoulder and Elbow Surgeons score. Results: This study enrolled 151 patients: 65 with cuff tear arthropathy, 54 with massive rotator cuff tears, 29 with glenohumeral osteoarthritis, and three with shoulder dislocations. Osteoporosis was identified in 37 patients. Subsidence occurred in 20 patients (13.2%). The mean FRmet was significantly lower in the subsidence ≥5 mm group (67.7% ± 6.2) than the <5 mm group (71.5% ±8.0, p=0.01). Logistic regression identified low FRmet (OR: 0.90, 95% CI: 0.82–0.99, p=0.03) and osteoporosis (OR: 3.2, 95% CI: 1.05–9.96, p=0.04) as significant risk factors. There was no significant difference in clinical outcomes with subsidence. Conclusions: Subsidence occurred in 13.2% of patients following RSA with press-fit short stems. A lower FRmet (<70%) and osteoporosis were significant predictors of subsidence. Achieving an FRmet ≥70% may reduce this risk, while cemented stems could be preferable for patients with osteoporosis. Level of Evidence: Level Ⅲ; Retrospective study; Retrospective comparative study; Diagnostic Studies