Dr. Troy Miles
What Are Hip Implants Made Of?
One of the most frequent questions I’m asked by patients in the course of a clinic day is what hip implants are made of. It makes sense that people would want to ask this question before having hip replacement surgery. After all, the chances are the hip implant we put in during surgery will stay with the patient for the rest of his or her life.
While the answer to this question is relatively straightforward—hip implants are made from titanium, polyethylene, and one of three materials for the ball—there is a little more to it once you go beyond the surface.
Taking a step back, there are essentially four parts of a hip replacement.
The Stem. This is the part that goes into the thigh bone or the femur.
The Cup. The cup fits in the socket of your pelvis.
The Liner. This fits inside the cup, which fits in the socket of your pelvis.
The Ball. The ball fits on the end of the stem.
In essentially all hip implants, the stem and the cup are both made out of titanium. This material is chosen not only because it has a great track record in terms of endurance, and it lasts a long time, but also because the strength properties and flexibility of the metal matches most closely to the same properties of our bone.
The liner of a hip implant is made out of a specialized plastic called polyethylene. This is the same material that has been used in hip implants for more than 50 years. In the last 15 years, however, there have been some significant advances in the way these materials are processed and created. In that same time period, the expected longevity of hip replacement implants has nearly doubled. With current estimates, we can expect hip implants to last up to 30 years or longer.
The area of the hip implant with the most variability, or the component that has the most variability, is the ball. This can come in one of three different materials that have very specific indications for use and theoretical benefits, in terms of implant wear and longevity. The first, and most common, material for the ball to be made from is cobalt chrome or a metal head. This is the traditional material used for hip replacements, and it has a great track record.
In just the last 15 years, there has been an increased focus on making implants last as long as possible, and there are now additional materials being used for the heads or balls on a hip implant. These include ceramic and oxidized zirconium. Ceramic heads are a much harder surface, and they are much more resistant to scratches, providing the theoretical benefit of a smoother interaction with the polyethylene liner. The theoretical risk with ceramic is that it is more brittle, and it is more prone to fracturing or breaking. Oxidized zirconium is an engineered metal alloy, which has a surface with the properties of a ceramic. This gives it the benefit of a ceramic ball, with a decreased risk of breaking, as it is a metal.
Regardless of what type of hip replacement implant we use in a particular case, the current research shows that all three types of head materials perform similarly and have essentially the same expectations in terms of longevity.
If you’d like to learn more about the options for hip replacement implants, I encourage you to contact my office at Shasta Orthopaedics in Redding, California, and schedule an appointment.