Weight of polyethylene wear particles is similar in TKAs with oxidized zirconium and cobalt-chrome prostheses

Abstract

Background: The greater lubricity and resistance to scratching of oxidized zirconium femoral components are expected to result in less polyethylene wear than cobalt-chrome femoral components.

Questions/purposes: We examined polyethylene wear particles in synovial fluid and compared the weight, size (equivalent circle diameter), and shape (aspect ratio) of polyethylene wear particles in knees with an oxidized zirconium femoral component with those in knees with a cobalt-chrome femoral component.

Patients and methods: One hundred patients received an oxidized zirconium femoral component in one knee and a cobalt-chrome femoral component in the other. There were 73 women and 27 men with a mean age of 55.6 years (range, 44-60 years). The minimum followup was 5 years (mean, 5.5 years; range, 5-6 years). Polyethylene wear particles were analyzed using thermogravimetric methods and scanning electron microscopy.

Results: The weight of polyethylene wear particles produced at the bearing surface was 0.0223 +/- 0.0054 g in 1 g synovial fluid in patients with an oxidized zirconium femoral component and 0.0228 +/- 0.0062 g in patients with a cobalt-chrome femoral component. Size and shape of polyethylene wear particles were 0.59 +/- 0.05 microm and 1.21 +/- 0.24, respectively, in the patients with an oxidized zirconium femoral component and 0.52 +/- 0.03 microm and 1.27 +/- 0.31, respectively, in the patients with a cobalt-chrome femoral component. Knee Society knee and function scores, radiographic results, and complication rate were similar between the knees with an oxidized zirconium and cobalt-chrome femoral component.

Conclusions: The weight, size, and shape of polyethylene wear particles were similar in the knees with an oxidized zirconium and a cobalt-chrome femoral component. We found the theoretical advantages of this surface did not provide the actual advantage.

Level of evidence: Level I, therapeutic study. See the guidelines for Authors for a complete description of levels of evidence.

Fig. 1

A CONSORT flow diagram shows enrollment, allocation, followup, and analysis.

Fig. 2A–B

Scanning electron microscope images show polyethylene wear particles from a Genesis II^® total knee prosthesis with (A) an OxZr femoral component (magnification, ×17000) and (B) a Co-Cr femoral component (magnification, ×27,000). Polyethylene particles in both groups are flaked and irregularly shaped (particles that cannot be described as round or spherical).

Fig. 3A–D

AP radiographs of both knees of a 59-year-old woman with osteoarthritis taken 5 years after surgery show the (A) Genesis II^® total knee prosthesis with an OxZr femoral component and the (B) Genesis II^® total knee prosthesis with a Co-Cr femoral component to be solidly embedded in a satisfactory position. There are no radiolucent lines or other signs of osteolysis around the tibial components. Lateral radiographs taken 5 years after surgery show the Genesis II^® total knee prosthesis with an (C) OxZr femoral component and the Genesis II^® total knee prosthesis with a (D) Co-Cr femoral component to be rigidly fixed in a satisfactory position. There are no radiolucent lines or other signs of osteolysis around the femoral, tibial, or patellar components.