The Oxford Partial Knee System from Biomet, a fully mobile-bearing partial knee replacement system, recently celebrated its 35th anniversary. The system is cleared by the FDA and has shown a 91 percent success rate in independent studies. Keith Berend, MD, of Joint Implant Surgeons in Columbus, Ohio, discusses the factors that contribute to Oxford's longevity and where partial knee replacements are headed in the future.
Q: What is unique about the Oxford knee that has allowed it to stick around for so long?
Dr. Keith Berend: One of the most important things that differentiates the Oxford group is during the development process, the designers strived to look at accurate research and outcomes for partial knee replacement; that has really driven the continued use of the procedure. The appropriate indication for performing the partial knee replacement has been defined as anterior medial osteoarthritis, which is about half of the patients we see in our office. Understanding the extended indications is one of the first things that has made Oxford different and led to its success.
Q: How has the research and development of the procedure impacted the implant and instrumentation design over the years?
KB: The implant is a fully congruent spherical femoral component that has the highest possible surface area and contact, which means there is low polyethylene wear. After a while, the Phase II instrumentation came out, which helped us more accurately balance the knee and prepare the surface of the knee within one millimeter or one degree of alignment. In the mid 1990s, the Oxford group introduced Phase III: a minimally invasive muscle sparing insertion procedure; this procedure prospered with the popularity of minimally invasive surgery in the past decade.
The Phase III procedure allowed us to implant with the same precision and accuracy of the earlier instruments. Surgeons at the Oxford implanted the first 1,000 patients with the Phase III device and followed those patients for five years. The surgeons reported a 96 percent success rate with the new minimally invasive instrumentation, which is especially great because the procedures were performed while the surgeons were still overcoming the learning curve.
Q: Where will this technology go from here?
KB: The implant that has been used to date is a spherical design with a single peg. This month, a double peg component was released to increase surface area and function in a more high-flex style so high flexion is almost always obtained. This increases fixation because you have an extra peg, which is a stepping stone to a cementless procedure. The biggest thing to hit the Oxford stage is the microplasty instruments, which are also being launched this month. They allow for even more accurate performance in terms of tibial resection, sizing and preventing impingement of the bearing onto bone or cartilage.
In the not-so distant future, we're going to see more patient-specific cutting guides and smart instruments like Signature guides. We've started using some of this technology with the Oxford and it's been incredibly accurate. Another study has come out to assess patient-specific cutting guides, finding they create a 45 percent better economic model for the hospital than using a robot for guidance. It's really fascinating; as this technology becomes more widely available in the partial knee, there is going to be an up-tick in procedures performed because of the cost-benefit.
Q: Where trends do you see for knee replacement surgery developing over the next few years?
KB: I think we're going to see a gross need for more partial and total knee replacements as baby boomers age. The aging population and obesity rates will increase, which is likely to drive up the number of patients who need surgery. However, to compare a partial to a total knee replacement isn't accurate; there isn't a minimally invasive surgery for total knee replacements. For the appropriate patients, we push toward better function and range of motion with partial knee replacements because patients are able to go back to work faster and return the activities they wouldn't be able to do with a total knee replacement. The needs of the patients will drive the physician interest in doing partial knee replacement.
Q: Partial knee replacements are sometimes described as a "band-aid" for the patient until they reach the point where they need a total knee replacement — how does new technology combat that notion?
KB: There have been studies presented at the American Association of Hip and Knee Surgeons meeting comparing the safety of the unicompartmental knee replacement to a total knee replacement. In one multi-center study, we found that the risk of a complication or re-operation was more than 11 percent with total knee replacements, but only 4 percent with partial knee replacement. The partial knee replacement procedure is also a minimally invasive surgery, which has several benefits for the patients who are appropriately indicated — it's important to understand the right indications. A lot of surgeons think we shouldn't do partial knee replacements because we'll just have to do the surgery all over again, but our data shows that isn't true. Long-term studies demonstrate a better than 91 percent implant survivorship at 20 years, that rivals total knee. Our own experience shows a 97 percent success at seven years in the first 1,000 consecutive Oxford partial knees we implanted.
Related Articles on Knee Surgery:
8 Points on Knee Arthroscopy in Surgery Centers
10 Points on Personalized Knee Replacements
Robotics in Orthopedic Surgery: 6 Points on the Present and Future
Q: What is unique about the Oxford knee that has allowed it to stick around for so long?
Dr. Keith Berend: One of the most important things that differentiates the Oxford group is during the development process, the designers strived to look at accurate research and outcomes for partial knee replacement; that has really driven the continued use of the procedure. The appropriate indication for performing the partial knee replacement has been defined as anterior medial osteoarthritis, which is about half of the patients we see in our office. Understanding the extended indications is one of the first things that has made Oxford different and led to its success.
Q: How has the research and development of the procedure impacted the implant and instrumentation design over the years?
KB: The implant is a fully congruent spherical femoral component that has the highest possible surface area and contact, which means there is low polyethylene wear. After a while, the Phase II instrumentation came out, which helped us more accurately balance the knee and prepare the surface of the knee within one millimeter or one degree of alignment. In the mid 1990s, the Oxford group introduced Phase III: a minimally invasive muscle sparing insertion procedure; this procedure prospered with the popularity of minimally invasive surgery in the past decade.
The Phase III procedure allowed us to implant with the same precision and accuracy of the earlier instruments. Surgeons at the Oxford implanted the first 1,000 patients with the Phase III device and followed those patients for five years. The surgeons reported a 96 percent success rate with the new minimally invasive instrumentation, which is especially great because the procedures were performed while the surgeons were still overcoming the learning curve.
Q: Where will this technology go from here?
KB: The implant that has been used to date is a spherical design with a single peg. This month, a double peg component was released to increase surface area and function in a more high-flex style so high flexion is almost always obtained. This increases fixation because you have an extra peg, which is a stepping stone to a cementless procedure. The biggest thing to hit the Oxford stage is the microplasty instruments, which are also being launched this month. They allow for even more accurate performance in terms of tibial resection, sizing and preventing impingement of the bearing onto bone or cartilage.
In the not-so distant future, we're going to see more patient-specific cutting guides and smart instruments like Signature guides. We've started using some of this technology with the Oxford and it's been incredibly accurate. Another study has come out to assess patient-specific cutting guides, finding they create a 45 percent better economic model for the hospital than using a robot for guidance. It's really fascinating; as this technology becomes more widely available in the partial knee, there is going to be an up-tick in procedures performed because of the cost-benefit.
Q: Where trends do you see for knee replacement surgery developing over the next few years?
KB: I think we're going to see a gross need for more partial and total knee replacements as baby boomers age. The aging population and obesity rates will increase, which is likely to drive up the number of patients who need surgery. However, to compare a partial to a total knee replacement isn't accurate; there isn't a minimally invasive surgery for total knee replacements. For the appropriate patients, we push toward better function and range of motion with partial knee replacements because patients are able to go back to work faster and return the activities they wouldn't be able to do with a total knee replacement. The needs of the patients will drive the physician interest in doing partial knee replacement.
Q: Partial knee replacements are sometimes described as a "band-aid" for the patient until they reach the point where they need a total knee replacement — how does new technology combat that notion?
KB: There have been studies presented at the American Association of Hip and Knee Surgeons meeting comparing the safety of the unicompartmental knee replacement to a total knee replacement. In one multi-center study, we found that the risk of a complication or re-operation was more than 11 percent with total knee replacements, but only 4 percent with partial knee replacement. The partial knee replacement procedure is also a minimally invasive surgery, which has several benefits for the patients who are appropriately indicated — it's important to understand the right indications. A lot of surgeons think we shouldn't do partial knee replacements because we'll just have to do the surgery all over again, but our data shows that isn't true. Long-term studies demonstrate a better than 91 percent implant survivorship at 20 years, that rivals total knee. Our own experience shows a 97 percent success at seven years in the first 1,000 consecutive Oxford partial knees we implanted.
Related Articles on Knee Surgery:
8 Points on Knee Arthroscopy in Surgery Centers
10 Points on Personalized Knee Replacements
Robotics in Orthopedic Surgery: 6 Points on the Present and Future