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Excellent Results with New Total Knee Replacement Implant

With more and more young and active adults of all ages developing knee osteoarthritis, there is a need for a long-lasting, durable knee replacement implant. Different implant designs have been developed and tried over the years. Some are held in place with cement. Others are cementless. There are unicompartmental implants, rotating-platform implants, and fixed or mobile bearing. Some implants have polyethylene (plastic) backing while others are all metal.

In this study, 10-year results with the rotating-platform, posterior-stabilized implant are reported. Specifically, one surgeon implanted 106 knees with the Press Fit Condylar (PFC) Sigma rotating-platform posterior-stabilized knee. Rotating platform implants are designed for longer life with less wear for the young, active, or overweight patient.

In a mobile-bearing knee, the polyethylene insert in the tibial (bottom half) component can rotate short distances inside the metal tibial tray. This rotation gives more rotation from side to side. In order to be a good candidate for this type of implant, the patient must have strong ligaments around the knee to support the implant. A stable joint is less likely to dislocate.

Up until now, there have been no studies that show mobile-bearing implants as the preferred choice for durability, improvement in pain, or improvement of function compared with a fixed-bearing design. Now with 10-years of data, there is a better idea of how well the PFC Sigma design works and holds up.

Patients ranged in age from 34 to 88 years old. Osteoarthritis of the knee was the main diagnosis for almost everyone in the study. Results were measured using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Knee Society pain score and functional score. X-rays and patient satisfaction regarding ability to perform daily activities and participate in sports or recreational activities were also used to measure outcomes.

Analysis of the data showed there was good to excellent results with significant improvements in pain and function. In fact, all of the implants were still in place at the end of 10 years, suggesting good long-term implant survival. Only a handful of patients had to have revision surgery for any reason. There were no implant failures caused by bone osteolysis (absorption or dissolving of bone) or implant loosening.

There were some reports of knee pain (14 per cent of the group) and crepitation (crackling sensation heard and/or felt). The authors recommend further study to find out what is causing these residual symptoms. For now, it looks like the PFC Sigma rotating-platform, posterior-stabilized design showed itself to be an excellent choice for durability and stability over time.

The rotational design and close fit of the components of this implant reduce cross shear forces. This, in turn, decreases wear and increases survival rates. Although this particular implant is usually reserved for young or active older patients, it was used quite successfully in this study with people of all ages.

References: Morteza Meftah, MD et al. Ten-Year Follow-Up of a Rotating-Platform, Posterior-Stabilized Total Knee Arthroplasty. In The Journal of Bone and Joint. March 7, 2012. Vol. 94A. No. 5. Pp. 426-432.

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