MAX Tibial Inserts Design Rationale

Knee Product Group

Optimized crosslinking

Crosslinking reduces wear, but it has been also been shown to reduce fatigue and fracture resistance. [1] Compared to the highly congruent hip articulation, the knee has more cyclic loading and higher contact stresses, making fatigue strength especially important for this application. [1,2] Thus, engineers optimized the radiation dose, ensuring MAX for knees has a crosslinking density comparable to 7 Mrad XLPE.

Mechanically-annealed, rather than melt-annealed

Currently available XLPE is melt-annealed to eliminate the free radicals that lead to oxidation and subsequent polymer degradation. The reduction in mechanical properties caused by melt-annealing is well-known. MAX is annealed using a proprietary mechanical compression process. This mechanical annealing eliminates free radicals—like melt-annealing—but does not diminish the mechanical properties of the polyethylene. [3,4]

*With both melt annealing and mechanical annealing, free radicals are eliminated to a level at or near the detection limit of ESR measurement equipment.