What is causing this pain in my hip?
Arthritis is a disease that involves the breakdown of cartilage that would otherwise allow the joint to move smoothly. The cartilage lines the articulating, or moving surfaces of the bone that makes up the joint. When the gliding surface that is formed by the cartilage is worn away, the bones grind against each other, causing pain and limiting joint movement.

Though researchers have labored for decades, arthritis continues to be an ailment without a non-surgical cure. The most common form of arthritis is called osteoarthritis, affecting an estimated 20 million Americans. This year alone, 200,000 Americans will be left with no alternative but to alleviate their pain through a hip replacement procedure.

Approximately 600,000 total joints are performed each year in the United States. An estimated 85-95 percent of these total joints will still be functioning after ten years, based on research reported in orthopaedic journals. How well your total joint performs depends on your condition prior to surgery, including your anatomy, your weight and activity level, and your willingness to follow your surgeon�s instructions before and after surgery, as well as the quality of the implant that your surgeon chooses and the orientation upon implantation.

Hip Replacement Today
Hip replacement is a surgical procedure that replaces the diseased ends of the bones which make up the joint. To accomplish this, surgeons use specially designed implants made from super-alloy metals and/or specifically manufactured Ultra High Molecular Weight Polyethylene. Using precisely engineered surgical instruments, the surgeon will remove the diseased portion and replace it with implants designed strictly for the hip joint.

Over the last quarter century, Ultra High Molecular Weight Polyethylene (UHMWPE) has been preferred for an articulating joint surface. Ultra High Molecular Polyethylene is a plastic material compatible with the human body that provides a low friction bearing surface. Although UHMWPE is an acceptable bearing for many patients, total hip replacements are being performed in younger and more active patients, who challenge the limitations of the standard material. In this decade, the focus of both science and industry has been directed towards defining the factors influencing polyethylene wear and developing new materials for the bearings in hip replacements. Even with the favorable clinical performance of the material, concerns over the possible biologic effect of wear debris have resulted in extensive research into improving this material and developing alternative materials. Today, material developments such as Metal-on-Metal and Ceramic-on-Ceramic are available for consideration for Total Hip Replacement. The following sections will discuss the potential benefits and associated wear rates with these different bearing materials.

Ultra High Molecular Weight Polyethylene�The Traditional Bearing Surface
Ultra High Molecular Weight Polyethylene has been used as a bearing surface in total joint replacement since the early 1960�s. This material is bio-compatible and provides a unique combination of properties including toughness and abrasion resistance, which is the dominant mode of wear in total hips. As a result of this unique combination of properties, UHMWPE material has demonstrated the ability to function well as a total joint bearing surface for periods exceeding 15 years. Wear rates associated with traditional polyethylene are on the order of 80 cubic millimeters, or a linear wear rate of .13 millimeters per year. Still, debris generated from the bearing surface is a concern in a small percentage of the population. Especially at risk are those patients under the age of 50 years old and active patients.

Polyethylene wear affects an implant by a biologic reaction known as �osteolysis.� During normal use polyethylene breaks down and wear debris is generated. The body can handle a certain number of polyethylene particles through its natural immune system. The number of particles and biologic response are different for each individual and are also dependent on activity level. If polyethylene particles become too numerous, overwhelming the body, osteolysis begins to take place and the bone is broken down. The implant may have a tendency to become loose and fail to function properly due to the loss of bone. The threshold for osteolysis is unknown, but wear rates of greater than .1mm per year greatly increase the risk of osteolysis.

Over the last century technological developments in medical devices have been prominent in the orthopaedic industry. In many cases, these advancements have led to improved survivorship, less cost and increased patient satisfaction. Biomet, Inc. has paved the way for many of new emerging technologies through a long-standing commitment and solid organizational structure focused on technology. In 1992, Biomet introduced the industry�s first improved polyethylene that has proven to reduce the amount of wear debris produced in-vivo (inside the body). Marketed under the trademark name ArCom, the material demonstrated a 40% reduction in wear compared to standard polyethylene. Stated in volumetric terms, the ArCom polyethylene produced annual wear rates of 48.7 cubic millimeters. This translates to a linear wear rate of .079 millimeters. This reduction in wear may potentially increase the life expectancy of the orthopaedic bearing. The increased wear-resistance of these components is a direct result of the thoroughly consolidated polyethylene material. This material has demonstrated the best combination of clinical history, mechanical properties, wear resistance, and resistance to degradation of any currently available UHMWPE.

Tomorrows Technology Today: Metal-on-Metal Articulation for Total Hip Replacement
Even though ArCom demonstrated a marked improvement in wear rates, supported by in-vivo results, development efforts continued in advanced articular surfaces such as metal-on-metal and ceramic-on-ceramic. In May of 2000, Biomet received clearance from the Food and Drug Administration to begin distribution on the M2A-Taper Metal-on-Metal Articulation. Validated by extensive research and clinical studies, the M2A-Taper promises to address the need for a low wear articulation in the young, and active patient.

The surgical procedure for a metal-on-metal device is exactly the same as that of a traditional polyethylene component. The only difference in the implants is that the polyethylene liner is replaced with a metal liner made from cobalt chrome. Cobalt chrome is a superalloy that is very hard and durable. It is identical to the material used for the femoral head. The wear resistance of cobalt chrome is very high.

The concept of a metal-on-metal articulating surface is not new. It should be noted that the use of all metal devices was not discontinued due to poor clinical performance, rather, new technology in the form of polyethylene bearing surfaces took over the market and has been the standard for the past 30 years. So, why is there now this renewed interest in metal-on-metal bearings?

Polyethylene wear debris and associated osteolysis continues to be the major contributor to implant failure in total hip arthroplasty. It has been well documented that the wear rates are 10 to 100 times lower with a metal-on-metal articular surface. Wear rates associated with metal-on-metal are reported at .4 cubic millimeters per year. This is a considerable reduction in the amount of wear debris generated.

The biggest potential risk associated with metal-on-metal devices is the possible increase in ion levels. It has been speculated that the metal debris generated from the bearing surface will potentially lead to cancer in years to come. To date, and this takes into account almost 35 years of research on metal-on-metal bearings, there are NO reports or increase incidences of cancer related to the use of a metal-on-metal hip articulation. In a published study, Visuri reported on 2164 total hip replacements with a follow-up of over 16 years; 579 patients received metal-on-metal articulations and 1585 received metal-on-polyethylene. In this study, Visuri determined how these total hip replacements compared to the general population on the incidence of developing cancer. The results showed that the metal-on-metal patients had a lower incidence of cancer than that predicted for the general population.

Future Alternative: Ceramic-on-Ceramic Articulation
The use of ceramic-on-ceramic bearings for total hip replacement dates back to the early 1970s. During this time, researchers were looking for a material, which had a greater wear resistance and thus would last for a longer period of time. After overcoming initial problems related to poor ceramic quality and fixation methods, it has been shown through controlled clinical studies that patients with a total ceramic acetabular system may have an opportunity to fulfill an active lifestyle with minimal wear to their artificial hip. Currently, ceramic-on-ceramic articulations are not cleared by the Food and Drug Administration for use in the United States. Many companies are currently involved in controlled clinical studies evaluating safety and effectiveness of the device.

Ceramic-on-Ceramic articulating bearings have proven to be highly bio-compatible, with sufficient strength and mechanical sliding characteristics. As in any joint replacement, the diseased or damaged hip is replaced. The ceramic on ceramic acetabular system consists of an outer metal cup and a hard, strong, non-metallic ceramic liner and modular head, and a metallic femoral stem. Polyethylene is often molded around the ceramic liner to help distribute the load more uniformly reducing the possibility of ceramic fracture. The safety of ceramic-on-ceramic bearings has been well documented in many publications. Ceramic has good wear characteristics and also has the lowest coefficient of friction, which reduces wear to a minimum.

Wear rates associated with ceramic-on-ceramic bearings are approximately .04 cubic millimeters per year. This is approximately 100 to 1000 times less than a traditional polyethylene bearing surface. With ceramic there is an increased risk of fracture compared to other bearing materials. However, testing of ceramic bearings have shown their ability to bear loads exceeding the human load requirements.

Conclusion
Today, there are several available bearing options for total hip replacement. These materials show promise in reducing the amount of wear debris generated from the articulating surface. The following chart graphically displays the associated wear rates of standard polyethylene, ArCom polyethylene, metal-on-metal and ceramic-on-ceramic bearings. Although clinical trials and testing have provided favorable results, one should consider the potential risk associated with these various surfaces. There is still a great necessity for ultra high molecular weight polyethylene and related products. This material may be better suited for some patients. These options should be discussed completely with your orthopaedic surgeon to evaluate the bearing that is best suited to your condition.

PUTTING TECHNOLOGY INTO PERSPECTIVE
All of us want the best possible healthcare available for ourselves and loved ones. While this is a worthy goal, one must remember that because a form of treatment is new, does not automatically make it the best choice for you. And, like it or not, the pressure to keep down medical cost is only going to increase over time.

These facts are particularly true in the treatment of hip and knee conditions requiring total joint replacement surgery.

Virtually none of the implants I use today existed in their present form five years ago. Does this suggest that those implanted ten years ago where inferior at the time? Of course not. It means that the implants available were selected as the best choice for each patient based on the technology and scientific evidence of the day. Fortunately, total joint surgery in The United States has been the beneficiary of massive ongoing technological evolution. This evolution has described certain �gold standard� principles that have been integrated and carried forward in implant development over the years since Dr. John Charnley performed the first total hip in England in 1958.

The exciting implant alternatives described in this newsletter simply represent recent great advances in total joint surgery that will increase joint longevity and ultimately reduce cost. These improvements do not mean we will �throw away� the previously utilized implants. Instead, as we have always done, the best technology for each individual patient will be selected for the highest quality result at the most cost-effective level.