There are many considerations facing patients and surgeons when choosing implants for hip replacement . The decision of hip replacement depends on factors such as patients' age, general health, quality of bone and level of activity. Eventually, bearing surfaces may wear out and need replacement. Cross-linked polyethylene hip replacement surface holds up better to wear over 6 years compared with the polyethylene product that is used conventionally. Cross-linked polyethylene is created by irradiating the material, breaking carbon bonds which can then be re-linked. The process produces a more wear-resistant plastic. It also allows use of larger femoral heads, which leads to greater joint stability.
Wear is defined as the progressive shedding of minute amounts of material from the implant due to friction or rubbing. Alternative bearings are considered highly wear-resistant and are an alternative to conventional polyethylene, which have traditionally had higher wear rates. Improvements are continually being made in materials used for hip implants, for instance:
   * Polyethylene durability has been improved through �crosslinking�
   * Highly crosslinked polyethylene, an advancement in this material, is highly wear-resistant
   * Current ceramic implants generally resist chipping and breaking better than the early versions
   * Second generation metal-on-metal products are designed to address loosening that sometimes occurred in first generation metal-on-metal implants
Clinical studies have shown that, generally, the higher the level of crosslinking, the greater the improvement in wear resistance. Zimmer's highly crosslinked polyethylene is produced using harmless high-dose electron beam radiation, which further links together the molecular structure of the polyethylene. Laboratory testing has shown that in crosslinking, a new three-dimensional structure is created that results in a polymer more resistant to wear. A study enrolled 171 patients (181 hips) who had received either the cross-linked or conventional plastic part, and the results showed 110% reduced wear for cross-linked versus conventional polyethylene at 6 years of follow-up. Evaluations included x-ray reading by clinicians who were blinded to the type of hip device used in each patient, and a validated, computer-assisted edge-detection method, as well as a rating of joint function.
Analysis of wear by the blinded and a computer-assisted method was performed at 6-month and 1-year intervals, which allowed for bedding-in of the joint replacement over the first year. The 2-dimensional wear rate was 0.01 mm/year for the cross-linked plastic joint and 0.17 mm/year for the conventional joint replacement ( P = .002).