Metalloceramic composite implants - Academy News at the 2007 AAOS Annual Meeting

Metalloceramic composite implants better for hypersensitive patients

The metalloceramic composite material, Oxinium, offers the same hypoallergenic properties of ceramics without their adverse material properties, and at a substantially lower cost, according to poster exhibit P194. The exhibit details a prospective comparison of ceramics and Oxinium in patients who have metal hypersensitivity.

Among 44 patients who had primary total knee arthroplasty (TKA) and 14 patients who had revision TKA in this study, there were no allergic reactions symptoms at a minimum of 2 years following surgery (range: 34 months to 130 months). The femoral components used were either ceramic (10 primary, 6 revision) or a metalloceramic composite (42 primary, 9 revision). Tibial components varied, but about half were all-polyethylene. All components were fixed with acrylic cement.

Metal hypersensitivity

Hypersensitivity to metals has been identified as a possible cause of arthroplasty failure. Although hypoallergenic ceramics are an alternative, their cost and material properties have restricted their application. Ceramics are brittle compared to the cobalt-based alloys used in most knee replacements and are subject to fractures as a result. Because of inherent limitations, neither alumina nor zirconia ceramics can be manufactured in the complex shapes available in metal. In addition to lacking full approval from the U.S. Food and Drug Administration (FDA), ceramic total knee implants are expensive, with some manufacturers charging as much as $5,000 for a single femoral component, up to five times the usual cost of these devices.

The composite material Oxinium has been suggested as another alternative. Oxinium is an alloy of 97.5 percent zirconium and 2.5 percent niobium. The articular surface is then oxidized to form the ceramic zirconia. Oxinium total knee femoral components have been available for more than six years, and are FDA-approved for general use. Prices vary, but at the authors’ institution, Oxinium implants cost approximately 50 percent more than a standard cobalt-chromium femoral implant.

In this study, metal hypersensitivity was documented by skin patch and in vitro leukocyte stimulation testing. Among the 44 primary TKA patients undergoing 51 knee replacements there were 39 women and 5 men ranging in age from 43 years to 79 years. Nine procedures used ceramic implants from various manufacturers, while 42 used Oxinium implants. Sixteen revision TKAs were performed in the 14 revision TKA patients (12 women, 2 men), aged 57 to 77 years. Seven of these implants were ceramic, nine were Oxinium.

No patients in the primary groups developed allergic reaction symptoms at a minimum of 2 years following surgery. Serial postoperative serum antibody and leukocyte studies have shown no reaction following placement of either type of knee.

(Left) Shortly after the patient had a TKA with a conventional metal implant, she began to show signs of severe metal allergic hypersensitivity, including pain, a rash mimicking psoriatic arthritis and limited motion. (Right) Radiographs of the same patient after revision to an alumina-ceramic implant: A “right femoral component,” the only type available at the time, was used in this left knee, without detrimental clinical results.

Revision TKA results

In patients who had revision TKA involving removal of a cobalt-chromium implant, preoperative symptoms of pain, effusion and eczematous rash rapidly resolved after the surgery. Serum studies showed a concomitant fall in antibody levels.

Among these patients were two individuals who underwent their second revisions. The previous revision TKA (9 years earlier in both cases) had used alumina implants, and both patients received a metalloceramic composite femoral implant. Neither developed adverse clinical symptoms or changes in antibody profile.

The authors conclude that this relatively small study strongly suggests that Oxinium offers the same hypoallergenic properties of ceramics without their adverse material properties, and at a substantially lower cost.

Researchers include Sam Nasser, MD, Michael P. Mott, MD, of Warren and Paul H. Wooley, PhD, all of Wayne State University in Detroit, Michigan. Dr. Nasser serves as a consultant to Smith+Nephew.

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