An important aspect of knee replacement surgery involves the choice of the knee implant type. There are several aspects to consider in selecting an implant type such as the degree of motion supported, the type of metal alloy used, cost and durability to name a few. For instance, a relatively younger patient who may wish to engage in physical activities may opt for high flexion implant. On the other hand, an elderly person who performs limited physical activities may be just fine with a normal implant that has a lower degree of motion.
An equally important aspect of any knee implant is about its durability. The typical life of an artificial knee implant ranges between 15 to 20 years. As time passes by, the knee implant undergoes the normal wear and tear caused by various form of stresses on the joint.
Given that the stress-induced wear and tear are to be expected, resulting in leakage of some metal debris into the joint area, it is important to choose metal alloys that are highly inert from biological aspects. A few such metal alloys are the Cobalt-Chromium and Oxinium.
Oxinium is a metal alloy containing 97.5% Zirconium and 2.5% Niobium. During the implant manufacturing process, it undergoes intense heat and oxygenation which allows Oxygen to be absorbed into the Zirconium metal. When Oxygen saturates the metal surface, it converts into a 5-micron thick Ceramic layer created over the metal core. In lab studies or also known as In-vitro studies, Oxinium is shown to have a lesser wear and tear relative to the more commonly used Cobalt-Chromium alloy. Lab results are based on thesimulated motion of the knee joint over a longperiod.
In-vitro lab reports have been used by its manufacturer (Smith & Nephew) who sell the Oxinium implants to claim its longer life as a result of lesser wear and tear. These implants also sell at a premium of 20-25% over the Cobalt-Chromium implants. However, several research studies that studied the performance of the implants in an In-vivo or inside the body environment failed to find any significant differences from a period ranging from two months after surgery to as long as five years. Further, even Cobalt-Chromium implants can easily last from 15 – 20 years.
Should you pay for the extra cost of Oxinium Implants?
The benefits that are associated with Oxinium but not proven by research include the following:
- Less than 0.0035% detectable Nickel, a metal that causes a reaction in some patients.
- Ceramic coating over metal resulting in lesser wear and tear, hence longer life.
- No known adverse information related to biocompatibility or other complications.
- 20% lighter weight compared to Cobalt-Chromium
An interesting research study analyzed forty patients at the North Sydney Orthopedic and Sports Medicine Center, who had undergone knee replacement in both legs. They had one knee implant with Cobalt-Chromium, and other was Zirconium. 
Patients were assessed at multiple stages after surgery i.e. five days, six weeks, one, two and five years. Standard outcome measures were evaluated including the WOMAC score, Knee Injury and Osteoarthritis Outcome Score and British Orthopedic Association patient satisfaction score. Results indicated no significant difference in clinical, radiographic or subjective outcomes at any stage. According to the study, 38% patients preferred the Cobalt-Chromium knee compared with 18% who preferred the Zirconium knee, with 44% patients having no preference for either. The study also demonstrated that both Cobalt-Chromium and Zirconium did not produce any adverse effects.
Besides the wear and tear of the metal components, another component which is subject to wear and tear is the polyethylene component that acts as acushion between the two metal heads. Damage to the polyethylene can result in various other impacts to the knee. Broken particles from the polyethylene can induce foreign body particle inflammation in the joint, which can then lead to Osteolysis or weakening of the femur or tibial bone head.
Therefore, a metal surface that can lead to lower polyethylene wear can be beneficial. However, again, in-vivo studies have failed to show any significant differences in the polyethylene wear between Oxinium and Cobalt-Chromium. 26 pairs of PE component were retrieved from patients who had undergone bilateral knee replacement, with one leg having a Co-Cr implant and other having Oxinium. The retrieved PE components were analyzed for damage assessment, wear assessment and radiographic assessment. All PE components displayed in-vivo damage such as grooving, indentation and pitting regardless of the implant type. No significant differences were noted in any of the three assessment aspects between Cobalt-Chromium and Oxinium implants. Another study also suggested the similar conclusion that there was no difference in the In-vivo PE component wear and tear between Co-Chromium and Oxinium implants. 
So what’s the key takeaway?
On the basis of research carried thus far, Oxinium has failed to meet the promises made for lesser wear and tear in the In-Vivo studies. At the same time, Oxinium implants have also not demonstrated any adverse effects and are considered to be as safe as the Cobalt-Chromium implants. It is ultimately for you and your surgeon to decide, but research does not indicate any extra benefit for the extra cost incurred in having an Oxinium implant. [1, 2, 3]
Have a question?
- Five-Year Comparison of Oxidized Zirconium and Cobalt-Chromium Femoral Components in Total Knee Arthroplasty: A Randomized Controlled Trial;Hui, Catherine; Salmon, Lucy; Maeno, Shinichi; Roe, Justin; Walsh, William; Journal of Bone and Joint Surgery, Volume 93 (7): 624 – Apr 6, 2011
- In Vivo Wear Performance of Cobalt-Chromium Versus Oxidized Zirconium Femoral Total Knee Replacements; Gascoyne, Trevor C.; Teeter, Matthew G.; Guenther, Leah E.; Burnell, Colin D.; Bohm, Eric R.; The Journal of Arthroplasty, Volume 31 (1) – Jan 1, 2016
- No difference in vivo polyethylene wear particles between oxidized zirconium and cobalt–chromium femoral component in total knee arthroplasty; Yukihide, Minoda; Kanako, Hata; Hiroyoshi, Iwaki; Mitsuhiko, Ikebuchi; Yusuke, Hashimoto; Knee Surgery, Sports Traumatology, Arthroscopy, Volume 22 (3) – Mar 1, 2014