Bicondylar Knee Implant System Incorporates PEEK-Optima CFR Polymer to Prevent Dislocation

A biocompatible polymer from Invibio is utilised as a bearing material for the axle bearings in a rotational knee system from Aesculap. The material is used to provide wear and cold flow resistance and dimensional stability.

Developed to combat the predominant causes of knee implant failure, luxation, wear and malpositioning associated with metal components, Aesculap's EnduRo knee revision system relies on PEEK-Optima carbon fiber-reinforced (CFR) polymer to increase the implant service life and reduce the necessity of subsequent revision surgery. Through use of PEEK-Optima CFR polymer, the service life of the EnduRo knee implant system’s rotational hinge mechanisms matches that of established primary condylar implants, according to the company.

The EnduRo knee implant from Aesculap


"Aesculap and Invibio have benefited from a long, mutually beneficial relationship based on sharing expertise and knowledge. It was through technical expertise, an understanding of our requirements and a long history of proven biocompatibility and implantation success that Invibio was able to provide us with an exceptional solution," says Dipl.-Ing. (FH) Ulf Grimm, Aesculap Product Manager for Knee Endoprostheses. "Throughout this process Invibio has provided valuable processing support and a manufacturing network with the flexibility and scope to meet our device and time targets,” Grimm adds. “Working with Invibio provided us with both a material and processing solution package that enabled our accelerated time to market requirement.”

The EnduRo knee implant is used in the treatment of severe bone defects and insufficiency of the ligamented apparatus. It has been commercially available in Europe since January 2010 and received US FDA 510(k) clearance in December 2010.

According to Aesculap, the EnduRo knee has received strong European market reception and gained a 14% market share in Germany during the first year of availability. In the United States, Aesculap received a strong launch into the market with the first implantation of the EnduRo knee implant in November 2011, according to the company.

Surgeon and Patient Benefits

In 2010, Millennium Research Group estimated there were more than 90,000 knee revision surgeries performed in the United States and Europe, indicating that some 8% of all knee implant procedures result from failure of the initial knee implant. A contributing factor to these failures is dislocation, whereby the rotational axis slips out of its guide, requiring total replacement of the implant. EnduRo`s hinge mechanism, joined cone design and the use of PEEK-Optima CFR polymer are intended to prevent dislocation compared to traditional hinge mechanism types that use ultrahigh molecular weight polyethylene (UHMWPE). PEEK-Optima CFR provides wear and cold flow resistance as well as dimensional stability during the lifetime of the device (>15 years), which aids resistance to dislocation. PEEK-Optima CFR is utilised as a bearing material for the axle bearings and also for the hinge ring bearing in femur.

According to Grimm, PEEK-Optima CFR provides valuable surgeon and patient benefits, including proven biocompatibility and biostability, flexural strength similar to the cortical bone, excellent wear performance and creep resistance and design flexibility.

In addition to providing significant patient benefits over primary condylar implants, the EnduRo knee design extends surgical options and minimises complexity. For example, using the EnduRo system cone connector to link the rotational axis and hinge ring of the femoral component, surgeons can eliminate the need for condylar drilling.

“The EnduRo rotational knee system is a bicondylar implant that, unlike other condylar implants, consists of only one hinged system (the linkage of the femoral and tibial components after these have been independently anchored in the bone) as opposed to three separate parts,” says Grimm. “The premounted hinge ring of the femoral component is simply placed over the proximal end of the prominent rotational axis, and both parts are then firmly joined together using a cone connector. Neither distraction nor additional condylar drilling is required.”