Abstract
Femoral components with an oxidized zirconium-niobium (OxZr) gradient ceramic surface (Oxinium, Smith & Nephew, Memphis, TN) were introduced as an alternative to cobalt-chromium (CoCr) alloy femoral components for the purpose of PE wear reduction in total knee replacements [1]. In the present study, the surface damage and clinical performance of both CoCr alloy and OxZr femoral components were investigated. By matching CoCr alloy and OxZr femoral components for clinical factors, as done by Heyse et al. [2], the surface damage on retrieved CoCr alloy and OxZr femoral component was assessed. Twenty-six retrieved cobalt-chromium (CoCr) alloy femoral components were matched with twenty-six retrieved oxidized zirconium (OxZr) femoral components for implantation period, body-mass index, patient gender, implant type (cruciate ligament retaining/substituting), and polyethylene insert thickness. Detailed surface profilometry was performed on retrieved femoral condyles in areas that had not been damaged by gouging [3] with the specific purpose of investigating the in vivo wear behaviour of undamaged OxZr surface. In addition, the cumulative survivorships were calculated for patients who had received CoCr alloy or OxZr femoral components from our orthopaedic database. In order to identify factors that affect the clinical performance of CoCr alloy and OxZr femoral components, the findings from the retrieval analysis and the survivorship analysis were combined. The Rp, Rpm, and Rpk-values for the retrieved CoCr alloy femoral components were found significantly higher than the Rp, Rpm, and Rpk-values for the retrieved OxZr femoral components (p ≤ 0.031). The roughness parameters values (Ra, Rq, Rz, Rp, Rpm, Rpk, Rv, and Rsk) for the retrieved CoCr alloy femoral components were found significantly higher than the values of the new, never implanted CoCr alloy femoral components (p ≥ 0.001). The surface roughness was higher on the medial condyles than the lateral condyles of the retrieved CoCr alloy femoral components; such a difference was not observed on the retrieved OxZr femoral components. The OxZr bearing surface appeared to protect the femoral components from abrasive wear in vivo. At 8.5-years follow up, the cumulative survivorship for the CoCr alloy femoral components (98%) was not found to be statistically significantly different (p = 0.343, Breslow test) from the OxZr femoral components (97.5%). Therefore, OxZr femoral components appeared to possess low wear characteristics and could be particularly suitable for younger, heavier patients to ensure long-term durability.
