This chapter discusses the advantages and complexities of ultra high molecular weight polyethylene (UHMWPE) when used as a bearing material for total joint arthroplasty (TJA) and total knee arthroplasty (TKA). The UHMWPE internal structure and its mechanical response depend strongly on a diversity of factors that include radiation crosslinking, fiber reinforcement, and the addition of antioxidants such as Vitam...