Humeral bone resorption after reverse shoulder arthroplasty using uncemented stem

BACKGROUND: Humeral stem loosening has gained attention as it has been identified as a cause of revision surgery in reverse shoulder arthroplasty (RSA). In RSA, humeral stem revision is very difficult if there is humeral bone loss because of stress shielding. Some studies of humeral bone resorption after anatomic shoulder arthroplasty have been published, but there are few detailed reports of humeral bone resorption after RSA. This study aimed to investigate the prevalence of humeral bone resorption after RSA procedures and to evaluate the risk factors for bone resorption. METHODS: This study included 48 shoulders that underwent RSA with an uncemented humeral stem from July 2014 to May 2017 and were followed up for more than 1 year. The prevalence of humeral bone resorption and risk factors were investigated. Logistic, multiple logistic, and multivariate logistic regression analyses were performed to evaluate the data. RESULTS: Grade 0 bone resorption, the most advanced grade, occurred in 8 shoulders (16.7%); grade 1, in 0 (0%); grade 2, in 17 (35.4%); grade 3, in 14 (29.2%); and grade 4, in 9 (18.8%). A high occurrence of bone absorption was observed in zones 1, 2, and 7. Grade 4 bone resorption did not occur in zones 3, 5, and 6. Female sex and an onlay-type stem were significant independent risk factors for grade 4 bone resorption. CONCLUSIONS: Bone resorption was frequently observed in the greater tuberosity, lateral diaphysis, and calcar region. Significant risk factors included female sex and an onlay-type stem.