A Rare Case of Metallosis Co-occurring With Chronic Prosthetic Joint Infection in Total Hip Arthroplasty

Prosthetic joint infection (PJI) and metallosis are known complications of total hip arthroplasty (THA) and are causes for revision surgeries. Articulating metal surfaces in total hip arthroplasty with corrosion at modular junctions can lead to the release of metal ions that can cause an immune-mediated biological reaction. There are few cases in the literature of both coinciding together. We describe a case of chronic Cutibacertium acnes PJI and metallosis co-occurring in a 64-year-old female after THA with a dual mobility construct. After undergoing uncomplicated left THA through a modified Hardinge approach, the patient dislocated anteriorly after four weeks and required revision of her acetabular component to a less anteverted position. Nine months later, she presented with hip pain and was found to have medial wall fragmentation and cystic changes around the greater trochanter on radiographs, elevated serum cobalt and chromium levels, and a benign noninfected hip aspiration. During her revision procedure, intraoperative histopathology showed over 20 neutrophils per high power field in multiple samples and fluid aspirates demonstrating Gram-positive rods. She was also found to have pseudotumor formation with the erosion of the anterior and posterior capsules with black debris on the femoral stem trunnion and the backside of the modular dual mobility liner. An antibiotic spacer was placed and her cultures grew into C. acnes. She completed six weeks of intravenous ceftriaxone and, during her "drug holiday," she dislocated her spacer and was found to have a lateral femoral diaphyseal stress fracture at the distal end of her spacer. She underwent stage II of her revision, and while the plan was to continue her antibiotics, she had an adverse reaction and was transitioned to oral antibiotics for six months. Due to delayed healing, she underwent additional irrigation and debridement with head and liner exchange. Her wound then healed, and at her one-year final follow-up, she was able to ambulate without pain, and her serum inflammatory and metal ion levels were within normal limits. Concurrent PJI and metallosis from articulating metal interfaces can occur, and a high index of suspicion is necessary to properly manage both conditions.