Case 1. A sixty-three-year-old woman (body mass index, 31.3) with severe osteoarthritis had undergone a left total hip arthroplasty with a 50-mm Trilogy Shell (Zimmer, Warsaw, Indiana), a 36-mm highly crosslinked polyethylene liner (Zimmer), an uncemented titanium-alloy ABG II size-3 modular femoral stem with a 130° cobalt-chromium MFN (Stryker, Mahwah, New Jersey), and a +5-mm 36-mm cobalt-chromium head (Stryker). The patient had an uneventful postoperative course and was discharged on postoperative day three.
Seven months later, the patient presented with progressive pain in the left hip. Radiographs showed satisfactory component positioning with no osteolysis, aseptic loosening, or periprosthetic fracture. Blood work showed an elevated erythrocyte sedimentation rate (ESR), C-reactive protein level (CRP), and serum metal ion levels without leukocytosis (Table I). Computed tomography (CT) of the hip demonstrated a 2.3 × 3-cm fluid collection between the gluteus maximus and medius muscles. Aspiration of the hip yielded 2 mL of orange-tainted fluid with a white blood-cell (WBC) count of 650 cells/μL with 96% polymorphonuclear cells. Gram stain, aerobic cultures, and anaerobic cultures were all negative. The patient had improvement of the hip pain after aspiration, but she returned to the clinic with recurrent pain. Metal artifact reduction sequence magnetic resonance imaging (MRI) demonstrated an 11.5-cm (diameter) fluid collection with a thick anterior wall effacing the posterior capsule and dissecting between the posterior soft tissues (Fig. 1). Concern for a metal-hypersensitivity reaction with inflammatory pseudotumor led to revision arthroplasty eight months after the index procedure.
Intraoperative findings demonstrated large necrotic areas surrounding the total hip arthroplasty, including all of the gluteus musculature, the short external rotator muscles, and both the anterior and posterior capsules. The femoral and acetabular components were solidly fixed, and the polyethylene liner showed no substantial wear; however, corrosion was grossly evident at the modular femoral neck-stem junction but not at the femoral head-neck junction (Fig. 2). Revision to a nonmodular Short Citation femoral stem with a ceramic head (Stryker) was completed without complication. The hip was stable on examination.
Analysis of the joint aspirate revealed a WBC count of 1950 cells/μL with 43% lymphocytes, and analysis of the bursal fluid found on initial entry into the fascia revealed a WBC count of 1750 cells/μL with 97% lymphocytes. All fluid and tissue cultures were negative for microorganisms. Histologic evaluation showed extensive necrosis and marked diffuse chronic inflammation (Fig. 3). There was no acute inflammation, and visible metal particles were very rare.
The patient had an uncomplicated postoperative course and painless gait at the one-year follow-up. Repeat blood work showed a decrease in inflammatory markers and serum metal ion levels (Table I). She experienced two posterior dislocations of the total hip arthroplasty, which were managed with closed reduction and standard hip precautions. Repeat MRI one year after the revision arthroplasty demonstrated continued inflammatory reaction adjacent to the prosthesis; however, the severity of these findings was diminished compared with the MRI obtained prior to the revision arthroplasty (Fig. 4).
Case 2. An active eighty-year-old woman with primary osteoarthritis had undergone a total hip arthroplasty with a 50-mm Trilogy Shell (Zimmer), a 36-mm highly crosslinked polyethylene liner (Zimmer), an uncemented titanium-alloy ABG II size-4 modular femoral stem with a 130° cobalt-chromium MFN (Stryker), and a +5-mm 36-mm cobalt-chromium head (Stryker). The patient did well initially, but she presented with a limp and persistent pain ten months postoperatively. Radiographs, CT, and peripheral WBC count were unremarkable, and all blood cultures were negative. Joint aspiration yielded turbid fluid with a WBC count of 28 cells/μL, a negative Gram stain, and negative cultures. Inflammatory markers and serum cobalt levels were elevated (Table I), and metal artifact reduction sequence MRI imaging showed intermediate signal in the soft tissue surrounding the arthroplasty, suggestive of early inflammatory reaction without frank soft-tissue disruption.
The patient underwent surgical exploration, removal of the femoral implant, and revision to a nonmodular ABG II size-5 femoral component with a ceramic femoral head (Stryker). Intraoperatively, pericapsular necrotic tissue extended inferiorly into the pseudocapsule and superiorly into the abductor and gluteus minimus muscles. Wear and corrosion were appreciated at the modular femoral neck-stem junction. Histology of periprosthetic tissue showed an extensive superficial layer of necrosis with underlying diffuse chronic inflammation without acute inflammation (Fig. 5). Postoperatively, the patient had good relief of pain and improved function.
Note: The authors wish to thank Hollis G. Potter, MD, Timothy Wright, PhD, Marcella E. Elpers, and Celeste Carlin for their assistance in the preparation of this manuscript.
Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.