Metal-on-metal hip replacements have been used in the United States for several years with studies showing good patient outcomes. However, concerns about the design have recently been raised after the DePuy ASR hip replacement recall occurred in July. For now, there seems to be a trend away from using metal-on-metal hip implants, but industry experts believe this trend won't last. Here are five reasons why metal-on-metal hip replacements will continue to remain in the spotlight.
1. Patients can develop soft tissue reactions to wear debris. One of the problems with using metal-on-metal hip replacements is knowing which patients are appropriate recipients. Most early concerns centered on implanting patients who had metal sensitivities despite the fact that with a metal-on-metal prosthesis, the cobalt and chromium levels in the patient's blood increase and then level off, says David Markel, MD, of St. John Providence Hospital. The implants had an association with soft tissue breakdown and pseudo-tumors as well as unexplained loosening. "Even though subspecialty surgeons were reporting these findings and that some patients were having problems, it wasn't enough to make a dramatic change in the market," says Dr. Markel.
2. The popularity of metal-on-metal could wane. DePuy Orthopaedics voluntarily recalled the ASR hip implant on July 17 citing the number of patients who required revision surgery. Since then, law firms around the country have filed suit against the company. The recall has caused concern among physicians and patients about the metal-on-metal design that could, at least temporarily, affect the sale and use of metal-on-metal hip implants. To combat the negative press towards metal-on-metal, some companies, such as Wright Medical Group, have issued releases detailing the studies that show the effectiveness of their implant's design.
"With DePuy's recall, there was a major domino effect," says Dr. Markel. "Just because one design went bad, it doesn't mean they all will.” However, the recall will most likely leave a long-term mark on the procedure. He says most surgeons will begin narrowing the indications for using metal-on-metal hip implants. "I suspect what is going to happen is that much like other popular things, the popularity of metal-on-metal hip implants is going to wane and that the metal-on-metal will find the appropriate niche," says Dr. Markel. "Many of the procedures we do grow rapidly and then settle down as we see which portion of the market they are good for."
3. Alternatives to metal-on-metal also have difficulties. There are proven alternatives to metal-on-metal hip replacements, such as ceramic-on-ceramic replacements. The ceramic-on-ceramic replacements perform well against wear, says Dr. Markel, but there are historic concerns with the implant fracturing and chipping. "There are also limitations relative to the materials as to how large the head can get," says Dr. Markel. The larger heads used for metal-on-metal replacements are advantageous because they provide increased stability and potential motion.
The other alternative to metal-on-metal is either ceramic or metal head against polyethylene liner. These are the most widely used materials. Recent modifications to the polyethylene material design, such as cross linking and use of free scavengers like vitamin E, have made use of polyethylene with large heads more viable. "We're just starting to see the early mid-term data and the wear characteristics are very good," says Dr.. Markel. "Several centers have been following patients closely and have seen that the wear patterns are great." There remain size limitations: as the size of the head increases there is a concomitant decrease in the thickness of the plastic. In comparison, metal-on-metal implants have a significantly larger head size for the similar cup diameter.
4. New technologies are available. Stryker has released a product in March, the ADM X3 Mobile Bearing Acetabular System, that has a cup similar to that of a metal-on-metal implant but pairs it with a large outer plastic ball with a smaller inner ball. "It's an interesting rediscovery of a French mobile bearing hip," says Dr. Markel. "At this point, the lab data has been very good relative to range of motion, stability and wear resistance." The company doesn't have the U.S. clinical reports of patient outcomes yet. The surgeries Dr. Markel has performed seem to have good outcomes. However, there is not enough data to say these implants are better than others. It is a very good alternative especially when you are treating a patient that presents a concern about stability, you can still give them a bigger head without having the problems associated with metal-on-metal implants," Dr. Markel says. Studies have shown that ADM with X3 have a 94 percent reduction in wear compared to metal-on-metal implants. The system's dual points of articulation help accommodate multi-directional movement, which provides a greater range of motion than fixed implant designs, based on laboratory testing.
5. AAOS supports appropriate use of metal-on-metal. The American Academy of Orthopaedic Surgeons supports the use of metal-on-metal hip replacements with caution instead of recommending against it, as the guideline for vertebroplasty does. The organization's news release on the subject states that the decision to have the surgery should be made after a discussion between the patient and the surgeon detailing the risks associated with the implant and other treatment options.
David Markel, MD, is a consultant for Stryker Orthopaedics.
Learn more about Stryker's ADM X3 Mobile Bearing Acetabular System.
Read more coverage orthopedic implants and procedures:
- Stryker's David Veino: In Support of Vertebroplasty
- Stryker's Oren Gelman Discusses Trends Toward the Single-Radius Knee Implant Design
1. Patients can develop soft tissue reactions to wear debris. One of the problems with using metal-on-metal hip replacements is knowing which patients are appropriate recipients. Most early concerns centered on implanting patients who had metal sensitivities despite the fact that with a metal-on-metal prosthesis, the cobalt and chromium levels in the patient's blood increase and then level off, says David Markel, MD, of St. John Providence Hospital. The implants had an association with soft tissue breakdown and pseudo-tumors as well as unexplained loosening. "Even though subspecialty surgeons were reporting these findings and that some patients were having problems, it wasn't enough to make a dramatic change in the market," says Dr. Markel.
2. The popularity of metal-on-metal could wane. DePuy Orthopaedics voluntarily recalled the ASR hip implant on July 17 citing the number of patients who required revision surgery. Since then, law firms around the country have filed suit against the company. The recall has caused concern among physicians and patients about the metal-on-metal design that could, at least temporarily, affect the sale and use of metal-on-metal hip implants. To combat the negative press towards metal-on-metal, some companies, such as Wright Medical Group, have issued releases detailing the studies that show the effectiveness of their implant's design.
"With DePuy's recall, there was a major domino effect," says Dr. Markel. "Just because one design went bad, it doesn't mean they all will.” However, the recall will most likely leave a long-term mark on the procedure. He says most surgeons will begin narrowing the indications for using metal-on-metal hip implants. "I suspect what is going to happen is that much like other popular things, the popularity of metal-on-metal hip implants is going to wane and that the metal-on-metal will find the appropriate niche," says Dr. Markel. "Many of the procedures we do grow rapidly and then settle down as we see which portion of the market they are good for."
3. Alternatives to metal-on-metal also have difficulties. There are proven alternatives to metal-on-metal hip replacements, such as ceramic-on-ceramic replacements. The ceramic-on-ceramic replacements perform well against wear, says Dr. Markel, but there are historic concerns with the implant fracturing and chipping. "There are also limitations relative to the materials as to how large the head can get," says Dr. Markel. The larger heads used for metal-on-metal replacements are advantageous because they provide increased stability and potential motion.
The other alternative to metal-on-metal is either ceramic or metal head against polyethylene liner. These are the most widely used materials. Recent modifications to the polyethylene material design, such as cross linking and use of free scavengers like vitamin E, have made use of polyethylene with large heads more viable. "We're just starting to see the early mid-term data and the wear characteristics are very good," says Dr.. Markel. "Several centers have been following patients closely and have seen that the wear patterns are great." There remain size limitations: as the size of the head increases there is a concomitant decrease in the thickness of the plastic. In comparison, metal-on-metal implants have a significantly larger head size for the similar cup diameter.
4. New technologies are available. Stryker has released a product in March, the ADM X3 Mobile Bearing Acetabular System, that has a cup similar to that of a metal-on-metal implant but pairs it with a large outer plastic ball with a smaller inner ball. "It's an interesting rediscovery of a French mobile bearing hip," says Dr. Markel. "At this point, the lab data has been very good relative to range of motion, stability and wear resistance." The company doesn't have the U.S. clinical reports of patient outcomes yet. The surgeries Dr. Markel has performed seem to have good outcomes. However, there is not enough data to say these implants are better than others. It is a very good alternative especially when you are treating a patient that presents a concern about stability, you can still give them a bigger head without having the problems associated with metal-on-metal implants," Dr. Markel says. Studies have shown that ADM with X3 have a 94 percent reduction in wear compared to metal-on-metal implants. The system's dual points of articulation help accommodate multi-directional movement, which provides a greater range of motion than fixed implant designs, based on laboratory testing.
5. AAOS supports appropriate use of metal-on-metal. The American Academy of Orthopaedic Surgeons supports the use of metal-on-metal hip replacements with caution instead of recommending against it, as the guideline for vertebroplasty does. The organization's news release on the subject states that the decision to have the surgery should be made after a discussion between the patient and the surgeon detailing the risks associated with the implant and other treatment options.
David Markel, MD, is a consultant for Stryker Orthopaedics.
Learn more about Stryker's ADM X3 Mobile Bearing Acetabular System.
Read more coverage orthopedic implants and procedures:
- Stryker's David Veino: In Support of Vertebroplasty
- Stryker's Oren Gelman Discusses Trends Toward the Single-Radius Knee Implant Design