A Randomized Controlled Clinical and RSA Study of 2 Total Knee Replacement Designs: A Comparison of Nexgen CR and Persona CR

Multiple factors may affect the outcome of total knee arthroplasty (1-5), and the patient satisfaction has been reported up to 90% (6). Also the physical behavior of a person may affect how much strain that is put on the prosthesis after surgery. Whether more strain is caused by a more physically active profile or by a more sedentary profile is uncertain. Obtaining real-life information about physical behavior is therefore important, and is made possible by using activity monitors measuring physical behavior continuously over longer time-periods.

The National Arthroplasty Registers worldwide has extensive data on knee and hip implants used over several years. Some are documented over 20 years, whereas newer implants appear with shorter follow-up. The Norwegian Arthroplasty Register has a registration completeness of 96% in the 2015 annual report (7).

NexGen is a total knee arthroplasty implant that has been used at great numbers in numerous countries and is well documented in several registries (Swedish Knee Arthroplasty Register, Australian Orthopaedic Association National Joint Replacement Registry).

Persona is a new implant from the same company that produces NexGen, with several changes and modernizations regarding instrumentation and surgical technique. There are a wider range of sizes available, both on the tibia and femur, as well as the menisceal insert. This should allow optimized component fit and less compromise on soft tissue balancing. The tibia is anatomical, with a more medialized keel stem, which should allow for a more accurate fit securing less risk of malrotation and better fixation.

The tibial component in the new Persona design, is anatomical, to achieve a better fit than in the old design. Additionally it facilitates proper rotation of the tibia. When a larger surface of bone is covered, it is expected a lesser risk of subsidence and early loosening of the implant. The new Persona also has a Vitamin E Highly Crosslinked polyethylene insert option for lower wear and improved strength than the regular polyethylene. However, the advent of newer highly crosslinked polyethylene has shown improved wear rates in hip arthroplasty, but not to the same degree in knee arthroplasty (8, 9). The investigators therefore will use conventional polyethylene in this study.