Implant sonication supporting the diagnosis of low-grade periprosthetic joint infection following reverse shoulder arthroplasty: a case report

Introduction Occult low-grade periprosthetic joint infection after reverse shoulder arthroplasty may mimic aseptic loosening because low-virulence organisms form implant-associated biofilm and may cause little systemic inflammation. Conventional tissue cultures may therefore remain negative. Case presentation A 72-year-old woman developed progressive pain and glenoid-sided osteolysis after reverse shoulder arthroplasty. Revision arthroplasty was initially performed for presumed aseptic loosening. Five periprosthetic tissue specimens remained culture-negative after at least 14 days of incubation, whereas qualitative sonication-fluid culture of the explanted components yielded methicillin-resistant Staphylococcus hominis subsp. hominis . Histopathology showed acute and chronic nonspecific inflammation with granulation tissue. Implant-retention management was followed by progressive osteolysis and component migration. The patient subsequently underwent complete component removal, debridement, insertion of a vancomycin-loaded spacer, antimicrobial therapy, and delayed hemiarthroplasty. At five months after reimplantation, the wound was healed and there was no clinical, laboratory, or radiographic evidence of recurrent infection. Conclusions Implant sonication provided additional microbiological evidence supporting low-grade periprosthetic joint infection despite negative prolonged tissue cultures. Because the initial sonication result was reported qualitatively without a colony count, it could not independently satisfy the quantitative EBJIS confirmatory criterion and required interpretation with the clinical, radiographic, histological, and microbiological findings.