- Developing artificial joints using ultra-high molecular weight polyethylene -

As the ratio of elders grows to 7% of the total population in 2000, Korea has already entered an aging society. As aging accelerates, the ratio of elders will be 14.4% in 2020, turning Korea into an aged society, and in 2026, the ratio will exceed 20%, entering a super-aged society. The aging process is increasing interest towards quality of life, and it is natural that elders desire a comfortable lifestyle.


As elders increase, more patients are suffering from degenerative joint disease in their knees. For people over 55 years old, 80~90% experience degenerative changes in their joints. Compared to Western countries, Korea has more patients suffering from arthritis because of its traditional ‘ondol’ (Korean under-floor heating) system that can cause stress to joints.


A joint is a body part where two or more bones meet. When a joint becomes inflamed, swelling and fever occurs, restricting free motion. Although inflammation might disappear in time, the joint keeps deteriorating and the patient has difficulty moving. This weakens muscles around the joint, and because of the weakened muscles, patients have a harder time moving. To overcome this vicious cycle, medical treatment to implant artificial joints may become necessary.


The basic materials used in artificial joint implantation include metallic, plastic and ceramic materials. Metallic materials are vulnerable to erosion and swelling caused by heat when used for an extended period of time. Plastic materials might cause osteolysis due to abrasion. Although the level of abrasion is low for ceramic materials, they crack easily. For these reasons, ultra-high molecular weight polyethylene or special ceramic material are used in joint connecting components. Having a molecular weight between 3,900,000~10,500,000g/mol, this material has outstanding properties against abrasion and friction. Furthermore, it has excellent biocompatibility. Since these materials can reduce physical pain as well as the economic burden resulting from repeated surgery, related research and patent applications are being made actively.


According to KIPO, the number of patent applications for fields related to ultra-high molecular materials used in artificial joints reached 120 during the past 5 years. In 2001, the number of applications was 15, while the number increased to 33 in 2005, showing an increasing trend each year. Though previous applications focused on technology to reduce abrasion of ultra-high molecular materials, recent attempts being made include applying nano-technology, radiation. Looking at the applicants, the number of foreign applications continuously increased from 13 to 33 between 2001 and 2005, while domestic applications decreased since 2003. In 2005, there were no related applications filed by a domestic applicant. Domestic research and patents related to artificial joints using ultra-high molecular weight polyethylene are in desperate demand.


The number of patent applications for fields related to special ceramic materials reached 112 during the past 5 years. The number has increased since 2002. The number of foreign applications increased from 9 to 17 between 2002 and 2005, while the number of domestic applications increased from 7 to 19.


Looking at technological fields, foreign applications showed an increasing trend for both ultra-high molecular weight polyethylene and special ceramic fields. Domestic applications showed a decreasing trend of ultra-high molecular materials used in artificial joints since 2003, while they showed a continuously increasing trend in special ceramic fields. As plastic abrasion might cause osteolysis, domestic research on artificial joint seem to be focusing on an alternative called special ceramic in order to prevent complications due to abrasion.


Last March, Ministry of Health and Welfare had announced “the standard of deciding the maximum cost for medical materials covered by National Health Service.” This announcement lessens the cost limitation of new medical products. Following this standard, the improvements compared to the products already registered in National Health Service are assessed and added to the price of new medical products. Based on this legislative foundation, acceleration to an aging society and the continuous increase of social interest towards quality of life, the technological development of artificial joints is expected to be active in the future.