High prevalence of early stress shielding in stemless shoulder arthroplasty

Abstract

IntroductionThe rates of early stress shielding in stemless total shoulder arthroplasty (TSA) in current literature are very low and inconsistent with our observations. We hypothesized that the incidence of early stress shielding in stemless TSA would be higher than previously reported. MethodsAll stemless TSA in a prospective database using a single humeral implant comprised the study cohort of 104 patients, of which 76.0% (79 patients) had a minimum one year radiographic and clinical follow-up. Radiographs were reviewed for humeral stress shielding, humeral radiolucent lines, and humeral or glenoid loosening/migration. Stress shielding and radiolucent lines were classified by location. Demographics and clinical outcomes, including American Shoulder and Elbow Surgeons (ASES) score and visual analog scale (VAS) pain score, were compared between patient cohorts with and without stress shielding. ResultsAt one year, 41.8% of patients had humeral stress shielding. Medial calcar osteolysis was seen in 32.9% of all patients and 78.8% of the stress shielding cohort. There were no cases of radiolucent lines or humeral or glenoid loosening/migration. There was no significant difference in age between cohorts (P = .308), but there were significantly more females (P = .034) and lower body mass index in the stress shielding cohort (P = .004). There were no significant differences in preoperative ASES (P = .246) or VAS scores (P = .402) or postoperative ASES (P = .324) or VAS scores (P = .323). ConclusionStress shielding in stemless TSA is more prevalent than previously published, largely due to infrequently reported medial calcar osteolysis. Stress shielding is more common in women and patients with lower body mass index. At early follow-up there were no significantly worse outcomes in the stress shielding cohort, but longer-term follow-up is needed to fully understand the impact of stress shielding on function and stability.