Section 2. Total Knee Arthroplasty
Knee Bearing Technology: Where is Technology Taking Us?

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Abstract

A novel sequentially irradiated and annealed bearing material (X3), characterized for use in knee arthroplasty, has been developed. Attention was directed to mechanical strength properties, oxidation resistance, and the ability to reduce wear. Material properties such as ultimate tensile and yield strength were unaffected by the sequential cross-linking process. Elongation was reduced relative to GUR 1020 conventional polyethylene, but equivalent to that of direct compression molded 1900 material. In knee simulator testing for normal gait and stair climbing, measured wear rates for X3 polyethylene were reduced by 79% and 77% when compared to the same knee design using conventional polyethylene. Mechanical properties and wear characteristics of the X3 polyethylene were unaffected before and after exposure to accelerated aging; properties of conventional polyethylene were adversely impacted.

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Materials and Methods

X3 is composed of GUR 1020 polyethylene, which is irradiated and annealed in 3 sequential steps—each consisting of 30 kGy of irradiation followed by annealing for 8 hours at 130°C in air. Following these 3 steps, the part is machined and gas plasma sterilized.

It is crucial that the bearing material properties be fully characterized. Further, the impact of time in the harsh environment of the host on these material properties must be investigated through an accelerated aging regimen. The

Results

Tensile yield strength and ultimate yield strength were statistically the same (P = .11 and .12, respectively) between the conventional and X3 polyethylene before accelerating aging (Table 1). Elongation for X3 was lower than for conventional polyethylene. However, it is comparable to that of direct compression molded 1900 material that has shown excellent clinical performance [8].

Further, the tensile properties of the X3 were statistically unaffected by the accelerated aging challenge.

Discussion

Satisfactory wear and mechanical performance of implant bearing surfaces may be dependent upon a number of factors, such as how well the implant is positioned, the demands of the host, the material properties, the locking mechanism, and the geometry of the design 9, 10. Care must be exercised by the surgeon to balance the soft tissues and appropriately align the knee. Technologies such as navigation may aid in accurate and reproducible positioning 11, 12, 13. Patient expectations should be

References (23)

  • S. Yau et al.

    Sequential irradiation and annealing of highly crosslinked polyethylenes: resist oxidation without sacrificing physical/mechanical properties

  • Cited by (0)

    No benefits or funds were received in support of the study.

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