Symptomatic Periarticular Fluid Collection After Total Hip Arthroplasty: Septic or Aseptic Complication? A Case Report and Literature Review

<b>Background and Clinical Significance</b>: Adverse reactions to metal debris (ARMD) are a rare but increasingly recognized complication following total hip arthroplasty (THA), with some studies suggesting upwards of 5% of metal-on-metal (MoM) and 3% of metal-on-polyethylene (MoP) prostheses being attributed to this. Historically, metallosis due to MoM implant design was the primary cause of ARMD. However, ARMD can also arise in metal-on-polyethylene (MoP) prostheses due to trunnionosis, which involves wear and corrosion at the modular femoral head-neck interface. Clinically, ARMD can resemble periprosthetic joint infection (PJI), complicating both diagnosis and management. <b>Case Presentation</b>: We present the case of a 40-year-old female with a history of systemic degenerative joint disease with bilateral MoP THAs who developed progressive pain and swelling in the upper left thigh, in which the prosthesis was first put in 22 years prior. The patient presented initially in a vascular surgery department for an infected iliopsoas cyst communicating with the hip where she had received surgery 2 years prior. The symptomatology reoccurred, and imaging revealed a large mass near the prosthesis and elevated inflammatory markers. Intraoperatively, a large volume of sero-purulent fluid was encountered, prompting a diagnostic workup for PJI. All cultures returned negative, and histopathology revealed macrophage-dominant infiltration with metallic debris, consistent with ARMD. After infection was definitively excluded, a revision THA was performed with an exchange of all modular components. The patient recovered without complications, and at six months follow-up, she demonstrated stable implant positioning, restored function, and no recurrence of symptoms. <b>Conclusions</b>: This case highlights the diagnostic complexity of PJI in joint arthroplasty and reveals the importance of a protocol-driven approach to exclude it prior to surgical revision. As the incidence of trunnion-related failure becomes more recognized in the literature, clinicians must consider ARMD in the differential diagnosis of late THA complications. Appropriate diagnosis is essential for guiding treatment and avoiding unnecessary complications, morbidity, and treatment related side-effects.