Types of Replacement Parts
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The materials used in artificial joints vary, depending on the type of joint being replaced and how the joint needs to function. Hip joints, for example, need to be sturdy and able to bear your body’s weight. Knee joints need to be flexible as well as strong, while finger joints must be capable of bending easily. In general, the components must be durable, flexible and able to function in the body without causing an immune system reaction.
Artificial joints have improved greatly since they were first introduced around 40 years ago. Replacements for hip and knee joints include portions made from metal, such as stainless steel, titanium or chrome and cobalt alloys. Other potions are made of a strong, durable plastic called polyethylene.
There are new types of knee replacement parts that are highly flexible, allowing the knee to bend up to 155 degrees. Not all people qualify for such a component; ask your surgeon. The pieces are designed to fit perfectly together and to function as closely as possible to a natural joint. Special bone cement is used in some cases to hold static parts of the artificial joint in place.
Some new implants are made of a special type of ceramic material or oxidized zirconium. A ceramic implant has a smooth surface that reduces the friction and wear on the joint that can result in the need for revision surgery. Ceramic implants are used primarily for hip replacements, as the material is too fragile to withstand the extensive weight and activity placed on the knees.
The zirconium implants are made of metal that has gone through a process that allows oxygen to absorb into the metal, creating a ceramic surface. These implants incorporate the benefits of a smooth surface with the benefits of a hard material, making it an ideal option for both hips and knees. While traditional implants last about 15 years, those made of these newer materials potentially can last up to 20 or 25 years. Another benefit of these new materials is that people who are allergic to metals can still use them.
Traditionally, replacement parts for finger joints have been made from silicone, in order to allow the flexibility required of fingers. However, this type of replacement has tended to slip somewhat because it does not fit tightly into the bones of the fingers. Researchers are working on new types of finger implants that are more like those used for knees and hips. These implants, like those for knees and hips, are made of metal and plastic materials that fit into the bones and more closely resemble a regular human joint. Researchers are still testing and perfecting finger replacements made of metal and plastic.
Cement Vs. Cementless Implants
In hip and knee joint replacement surgery, there are two types of replacements to consider: cemented and cementless, or a hybrid (combination) of cemented and cementless. The difference between the two types is how they are held in place.
The cemented version, as the name implies, uses a special kind of bone cement that helps hold the components of the artificial joint in place With cementless joints, the components that fit inside the bone are made of a porous material that allow the natural bone to grow into it.
Each type of implant has advantages and disadvantages. The cemented version may be better for older, less active people. That’s because sometime portions of the cement can break away, allowing the implant to loosen a bit. However, bone cement and surgical techniques have improved over the years so that cemented implants can work for younger and more active patients as well. Cementless versions may last longer, in some cases, because there is no cement to loosen. However, these implants aren’t a viable option for everyone. You need to have bones that are in good shape so they can grown into the prosthesis. (Cemented implants are generally a good choice for people with osteoporosis , a disease marked by porous, brittle bones.) Plus the recovery takes a bit longer with cementless joints because the bone requires time to grow.
In addition, one version may work better than another depending on which joint is being replaced. Some surgeons also use a combination of the two methods of fixation. For example, some research has shown that cemented implants are more successful for knee replacements than the cementless version. In hip replacements, the cementless approach can work better for the acetabular portion (the upper part of your leg), while cement may be needed for the femoral component (the lower part of your leg). The combination is common in hip replacement surgery. In addition, there are new, minimally invasive knee and hip procedures that may be used in some situations. They require less cutting and less recovery time.
How do you determine the kind of implant that is best for you? You’ll need to talk with you doctor about the advantages and disadvantages of each one. Many factors, such as your age, weight, bone strength, the joint being replaced and even the shape of your bones should be considered. Your doctor can help you decide which implant will work best for your body and lifestyle. Be honest with your doctor about your fears and concerns.
