Metallosis and elevated serum levels of tantalum following failed revision hip arthroplasty— a case report

Abstract

A 70-year-old woman had a primary cemented total arthroplasty of her right hip performed elsewhere in 1967 for developmental hip dysplasia. The arthroplasty failed in 1977, due to aseptic loosening and since then the patient has undergone 3 revision procedures including 2 acetabular cup revisions. In 2006, a porous tantalum acetabular augment (PTAA) (Zimmer, Warsaw, IN) was used to support a hemispherical cementless acetabular centroid Hilock cup (SYMBIOS Orthopedie, Yverdon-les-Bains, Switzerland) made of titanium alloy (Ti6Al4V) with a porous titanium and hydroxyapatite dual coating. At that time, no cement was interpositioned between the cup and augment—as instructed by the manufacturers. 6 years later, the patient was unable to walk and suffered severe pain, and she was referred to us for an additional revision. The preoperative radiographs showed a peculiar “halo formation” surrounding the acetabular component (Figure 1). Extensive metallosis of this surrounding tissue was found intraoperatively. Black pigmentation was also found in the overlying skin (Figure 2). Following the removal of the loose Hilock cup, the tantalum augment was found to be non-osseointegrated, severely worn, and broken (Figure 3). Debridement and synovectomy was performed and a modified cup-cage construct technique was used to address the existing pelvic discontinuity. Figure 1. Pre-revision radiograph. An unexplained “hallo formation” can be seen surrounding the acetabular components. Figure 2. Skin pigmentation immediately after revision. Figure 3. Intraoperative findings. Extensive periprosthetic metallosis and wear of the tantalum augment and the adjacent porous titanium and hydroxyapatite-coated acetabular SYMBIOS cup. Ta particles were embedded in the polyethylene surface (black stains). 2 peripheral blood samples were taken just before the revision operation and periprosthetic tissue samples were taken intraoperatively using a standardized technique for minimizing any potential risk of contamination during collection or handling. Quantitative determination of metal levels in serum and tissue samples was performed after the dissolution of the samples. The serum samples were diluted 10-fold with 0.14 M high-purity nitric acid in double-distilled water, and the tissue samples were digested in a temperature-controlled microwave oven (Milestone START D) (Rodushkin et al. 2004). Due to the very low concentrations of tantalum in serum reported in the literature (in the nanogram-per-liter range), the Ta content of the solutions was determined by inductively coupled plasma-mass spectrometry (ICP-MS) for the 181Ta isotope using the Agilent 7700 ICP-MS spectrometer with an octopole reaction system to eliminate possible interferences (Rodushkin et al. 2004). For study of the morphology of the tissue surface, and for semi-quantitative analysis (FEI company), a Quanta 200 scanning electron microscope (SEM) equipped with an EDX-Genesis 400 energy-dispersive X-ray fluorescence spectrometer (EDX) was used under low vacuum, without any pretreatment of the samples. The SEM image showed an alteration on the surface of the largest part of the tissue (Figure 4). The semi-quantitative EDX analysis of area A revealed a composition with Ta as the predominant element, accompanied by Cr and Co (Ta: 76.2%; Co: 6%; Cr: 2.9%; C: 6.3%; O: 7.3%; S: 0.7%; and Ti: 0.6%). Figure 4. SEM image and results of EDX analysis of areas A, B, C, and D revealing the predominance of Ta. Spot analyses of areas B and C showed almost pure pieces of Ta (88% and 75%, respectively) laid on the tissue. Area C showed a small increase in the titanium concentration (1%). EDX analysis of area D, considered to be rather free of depositions, showed a composition of C: 31%; N: 18%; O: 32%; Na: 0.5%; S: 1%; Ca: 0.4%; Ta: 18%; and Ti: 0.3%) with a reduced content of Ta in comparison to the previous examined spots B and C. The Ti level was close to the detection limit. The actual values of tantalum serum levels determined in both preoperative serum samples were 20 (SD 2) μg/L. These values were approximately 2,000 times higher than what has been reported in the literature, which is in the 0.008–0.010 μg/L range for normal serum samples (Rodushkin et al. 2004). The total concentrations of Ta and Ti in the investigated tissue sample were 35% and 0.6% respectively. No clinical signs of systemic ion toxicity were identified, and markers of liver and kidney function were within the normal range. At re-revision, as there was pelvic discontinuity we used a modified cup-cage concept using a jumbo Ta acetabular cup and distal augment, which were protected by a Ti Burch Schneider-type reconstruction ring—Contour (Smith and Nephew, Memphis TN)—with Palacos cement in all implant interfaces. 6 months after revision, the serum tantalum levels were 15 μg/L, a decrease of 25% compared to the levels found in the serum just before revision operation. The patient had no pain (Figure 5). Figure 5. 6 months after re-revision of the acetabular components. A modified jumbo Ta cup-Ti cage construct and peripheral Ta augment were used due to pelvic discontinuity. The patient had no pain at the latest follow-up.