A minimum 5-year follow-up of an oxidized zirconium femoral prosthesis used for total knee arthroplasty
Introduction
Total knee arthroplasty (TKA) is a commonly utilized surgical procedure to alleviate pain and improve function in patients suffering from end stage arthrosis of the knee. The survivorship of TKA prostheses has been reported to be greater than 90% 10 years postoperatively in several studies of unselected patients [1], [2], [3], [4], [5]. However, with greater follow-up, polyethylene wear and osteolysis become increasingly prevalent and can jeopardize the longer term survivorship of the implants [6], [7], [8]. Thus, there has been an effort to increase the longevity of TKA prostheses by improving the wear characteristics of the articulation between the femoral prosthesis and polyethylene insert. Much emphasis has been placed on the manufacturing of more wear resistant articulations through conforming designs, better sterilization methods, and cross-linking of the polyethylene. Another potential method of reducing prosthetic wear is to improve the femoral bearing surface by utilizing ceramic surfaces, such as oxidized zirconium instead of cobalt-chromium alloys.
Zirconium is a metal with properties similar to titanium. The oxide of zirconium, referred to as “zirconia” (ZrO2 or zirconium dioxide), is a commonly utilized ceramic material. Although zirconia ceramic implants have been utilized for femoral head prostheses in total hip arthroplasty (THA) for decades, concerns regarding potential in vivo breakage have prohibited its use in the field of knee arthroplasty. In recent years, however, oxidized zirconium has been introduced as a metal-ceramic hybrid material used for both knee and hip arthroplasties. Unlike pure zirconia ceramics, oxidized zirconium consists of a solid metallic zirconium core substrate with just the surface layer transformed to a zirconia ceramic. The resulting material shares the breakage resistance of the metal zirconium, while also exhibiting the favorable wear characteristics of the ceramic-bearing surface zirconia. Wear simulator studies in several different laboratories comparing oxidized zirconium to cobalt chromium have demonstrated a reduction in polyethylene wear from 42% to 85 % [9], [10], [11], [12]. Because oxidized zirconium contains no measurable nickel content, the material is felt to be safe to use in nickel-sensitive patients undergoing TKA. Although oxidized zirconium has been used in TKA since 1997, to date there has been a paucity of clinical outcome data to gauge the safety and efficacy of this material [13], [14], [15]. As is the case with all new prosthetic devices and prosthetic materials, there always remains a possibility that novel technology may not produce the same outcomes in vivo as was predicted from in vitro studies, and in many instances, the results of novel technology have been inferior to pre-existing technology [16], [17], [18], [19], [20], [21], [22], [23]. Therefore, clinical follow-up studies of patients with novel prosthetic devices are mandatory. The purpose of the current investigation is to document the minimum five year clinical and radiographic outcomes associated with oxidized zirconium femoral components utilized for TKA.
Section snippets
Methods
A retrospective review of prospectively entered clinical data was undertaken on 109 consecutive TKAs in 82 patients, all of whom had an oxidized zirconium femoral component (Genesis II, Oxinium, Smith and Nephew, Memphis, TN). Institutional review board approval was obtained prior to the review and all patients gave written consent prior to enrollment in our institution's total joint registry. Unilateral TKA was performed in 55 patients (55 TKAs), whereas 25 patients had simultaneous bilateral
Results
Clinical results are summarized in Table 1. The mean Knee Society score preoperatively was 50 (range, 57–81), and at last follow-up at a minimum of five years was 92 (range, 49–100). The mean Knee Society Function score was 55 (range, 8–90) preoperatively and increased to 81 (range, 30–100) at minimum five-year follow-up postoperatively. Mean knee range of motion increased from 111 (range, 57–150) preoperatively to 117 (range, 55–140) postoperatively. The mean UCLA activity score at a minimum
Discussion
This study evaluated the mid-term results of over 100 TKAs performed with an oxidized-zirconium femoral prosthesis in a relatively young, active cohort of patients with a minimum follow-up of five years post-operatively (range, 5–10 years; mean, 5.9 years). To date, this is the longest reported follow-up and the largest cohort of patients with this prosthesis that we are aware of. Although this prosthesis has been previously shown to reduce polyethylene wear in knee wear simulators [9], [10], [11]
Conflict of interest statements
Dr. Ezzet consults for Smith and Nephew and receives research support from Zimmer. Dr. Hofer has no conflicts to report.
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