30 year knee wear testing
Using an internationally accepted testing protocol, our LEGION Knee with LEGION◊ CR Knee with OXINIUM◊ Technology and XLPE was placed alongside identical implants made from cobalt chrome and a standard plastic liner and cobalt chrome and an XLPE liner into a sophisticated machine that continually simulates the cycle of movement required by a normal walking motion. Each cycle is equivalent to the range of movement required for an average person to take a step.2 The combination of OXINIUM Technology and XLPE was formerly known as OXINIUM◊ Technology. (See Important Testing Note below)
We understand that "30 years of wear performance" is a pretty significant statement for any implant manufacturer to make. That's why we want you to see how we can back it up.
Initial testing
Using an internationally accepted testing protocol, our LEGION Knee made with the combination of our proprietary OXINIUM◊ metal alloy and a highly cross-linked plastic insert was placed alongside identical implants made from cobalt chrome and a standard plastic liner and cobalt chrome and an XLPE liner into a sophisticated machine that continually simulates the cycle of movement required by a normal walking motion. Each cycle is equivalent to the range of movement required for an average person to take a step.2
During the first phase of testing, all three implant types were placed under a load of 899 pounds, or 4.9 times the typical body weight of a knee replacement patient (185 pounds), while the machine completed 5 million cycles. The machine was then stopped and all of the implants were carefully measured to determine how much wear had occurred to the metal and plastic components. The results from this first phase of wear testing very encouraging.
Continued testing
Armed with the data from the first 5 million cycles, we decided to continue "walking" the LEGION CR Knee with OXINIUM Technology and XLPE Implant out to 45 million cycles - the equivalent of 30 years of an active adult's life under typical conditions.3-9
After a total of nearly three years of continuous laboratory wear testing, the results surpassed even our high expectations.
After 45 million cycles, the LEGION CR Knee with OXINIUM Technology and XLPE showed 81% less wear - even when compared to the cobalt chrome knee that was stopped after only 5 million cycles.
Why 45 million cycles?
Based on scientific literature reviews, a person who undergoes knee replacement surgery at the relatively young age of 45 years old would subject the implant to between 36 and 44 million cycles over a 30-year period, depending on how active the person's lifestyle is. Smith & Nephew chose the high end of this range - 45 million cycles - as the simulated 30-year mark.
Important testing note
The wear testing and results referenced here apply only to the LEGION CR Primary Knee made with OXINIUM Technology and XLPE only. Extended lab-testing for other knee systems have not been performed. The results of laboratory wear simulation testing have not been proven to predict actual joint durability and performance in people. A reduction in wear alone may not result in improved joint durability and performance because other factors, such as bone structure, can affect joint durability and performance and cause medical conditions that may result in the need for additional surgery. These other factors were not studied as part of the testing.
Important safety notes
Knee replacement surgery is intended to relieve knee pain and improve knee functions. However, implants may not produce the same feel or function as your original knee. There are potential risks with knee replacement surgery such as loosening, fracture, dislocation, wear and infection that may result in the need for additional surgery. Longevity of implants depends on many factors, such as types of activities and weight. Do not perform high impact activities such as running and jumping unless your surgeon tells you the bone has healed and these activities are acceptable. Early device failure, breakage or loosening may occur if you do not follow your surgeon's limitations on activity level. Early failure can happen if you do not guard your knee joint from overloading due to activity level, failure to control body weight or accidents such as falls. Talk to your doctor to determine what treatment may be best for you.
References
- ASTM F2384.19404-1 and ASTM F75.17485-1
- ISO 14243-3
- R. Papannagari, G. Hines, J. Sprague and M. Morrison, "Long-term wear performance of an advanced bearing knee technology," ISTA, Dubai, UAE, Oct 6-9, 2010.
- Goldsmith AA et al., "Comparative study of the activity of the total hip arthroplasty patients and normal subjects". J Arthrop, (16)5:613-619, 2001.
- Morbidity and mortality weekly report, 55(40):1089-1092, October 13, 2006.(//www.cdc.gov/mmwr/preview/mmwrhtml/mm5540a2.htm?s_cid=mm5540a2_e. Accessed on October 30, 2009).
- Gioe TJ et al., "Knee Arthroplasty in the young patient - Survival in a community registry". Clin Orthop Relat Res, 464:83-87, 2007.
- Wallbridge N and Dowson D. "The walking activity of patients with artificial hip joints". Eng Med 11:95, 1982
- Wimmer M A et al., "Joint motion and daily activity profile of total knee patients in comparison with the ISO knee wear simulator". Paper 0159, 48th ORS, 2002. - 8 Huddleston J I et al., "How often do patients with high-flex total knee arthroplasty use high flexion?",Clin Orthop Relat Res, 467:1898-1906, 2009.
- Naal F D et al., "How active are patients undergoing total joint arthroplasty? A systematic review", Clin Orthop Relat Res, DOI 10.1007/s11999-009-1135-9, published online: 28 October 2009.
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