Dr. Wolfgang Fitz: Advancing Orthopedic Biotechnology and Partial Knee Replacements
November 17, 2008
By: Loren Kalm for Knee1
Dr. Fitz is an associate orthopedic surgeon at Brigham and Women's, Falkner and New England Baptist Hospitals in Boston as well as an Instructor at Harvard Medical School. Since his arrival at the Brigham he has worked on patented innovations including the use of nanotechnology to improve the performance of bone cement and on implant design. He was one of the design surgeons for the surgical technique and instrumentation for minimally invasive total knee replacement. Additionally, he has worked on instrumentation and technique of computer assisted joint replacement technology to improve outcomes in arthroplasty. Currently he is a member of the Scientific Advisory Board for Conformis Inc., working on personalized mini-invasive knee uni-, bi-compartmental and total knee replacements. Dr. Fitz won the National Orthopaedic Fellowship Foundation Award in 1999 and was selected a John Insall Traveling Fellow in 2002 by the American Knee Society.
Knee1: What are some of the risk factors for developing knee osteoarthritis?
Dr. Fitz: There are primary and secondary risk factors. Primary risk factors include age over 50, obesity, genetic disposition, female gender and abnormal bone density. Secondary risk factors include: previous sport injuries to the knee and repetitive stress injuries such as kneeling, squatting e.g. in certain professions such as carpet laying. High impact sports such as long-distance running or playing tennis are also risk factors, along with some rarer metabolic or congenital disorders or repeated episodes of gout or septic arthritis. Studies also show that certain disorders such as low intake of Vitamin C or D, poor physical fitness, or either bow or knock knees accelerate the progression of osteoarthritis.
Knee1: What are some of the indications that a patient is in need of a knee replacement surgery rather than an alternate route.
Dr. Fitz: In general, knee replacement surgery is elective surgery, and if surgery goes well, activities of day living will improve. If pain and limitations occur, which limit daily activities, patients may consider knee surgery if alternate treatments have failed.
Knee1: What are the limitations of knee replacement surgery? Will patients be able to perform the same activities that would be able to do if they had elected not to have surgery?
Dr. Fitz: The goal of successful knee replacement surgery is to have patients be able to return to the same activities they were able to do before surgery without pain.
Knee1: You were instrumental in developing computer assisted surgery (CAS) as a technique for proper alignment in knee replacement surgery. What are the benefits of this technology, and is its use becoming the standard of care for knee replacement procedures?
Dr. Fitz: Studies show that several factors are important for good long-term results after knee replacement surgery. One of these factors is an appropriate positioning of the tibial component along the mechanical axis of the shin-bone. Computer assisted surgery is a helpful tool to avoid outliers, but it adds cost, surgical time and morbidity, such as the rare possibility of a fracture. Other factors such as patient selection and soft tissue balancing are equally important. High volume surgeons using long leg films and pre-operative planning align their components reasonably well. Soft tissue tensioning is even more important and computer assisted surgery may help the advanced, computer savvy surgeon.
I prefer using a special tool measuring the tension of the soft tissue envelope to ensure appropriate soft-tissue balancing. Applying a certain tension of the ligaments in every patient, results in a stable balanced knee replacement and patients feel immediately that their knee is stable after surgery. They can move it, and are able to bear weight much sooner. Unstable knees, which have too much laxity and are very often painful, result in longer and more complicated rehabilitation. The additional benefit of using a knee tensiometer is that the femoral component is positioned slightly more externally rotated to reduce or even eliminate tracking problems of the knee cap. This is even more important with smaller incisions since it is very difficult to rely on anatomic landmarks to determine the rotation of the femoral component. Generally, computer assisted surgery in knee replacement has been performed less frequently in the last year in the US and Europe. Currently manufacturers are working on simpler tools for surgeons.
Knee1: What should patients know about the procedural differences between minimally invasive knee replacements and standard techniques?
Dr. Fitz: First, we have to differentiate between a partial or unicompartmental knee arthroplasty (UKA), or total knee arthroplasty (TKA). I feel that partial knee replacements are less invasive than total knee replacements. UKAs require less bone resection, preserve more soft tissue and preserve the anterior cruciate ligament. We estimate that somewhere between 25% to 35% of patients considering knee replacement surgery are candidates for partial knee replacements, but the total numbers of partial replacements done in the US was only 8% in 2007. The function of the knee after a UKA feels more normal and the range of motion is better than that of a total knee replacement. Even the peri-operative morbidity of thrombosis, embolism and infection is less. In regard to procedural differences between a standard and a minimally invasive or better small approach for total knee replacement, the difference lies more in the total amount of soft tissue trauma caused during surgery. It is not the length of the skin incision that matters. Some surgeons feel that flipping the patella may add trauma. The amount of damage cutting into the quadriceps tendon has failed to correlate with quicker recovery. Some surgeons feel that going less than 2 cm proximal into the quad tendon may accelerate recovery. However, several studies have failed to prove this hypothesis and have shown that the benefit of less tissue trauma during total knee replacements is very marginal.
It is important to obtain good visualization during surgery by being able to visualize anatomic landmarks to place the components in good positions, and to avoid intra-operative errors that may jeopardize short- and long-term outcome. In the last several years we have changed multiple variables that may contribute to a quicker and easier recovery. We modified patient’s expectations, changed our peri-operative pain management from PCA’s and epidurals to better oral pain medications infiltration of local anesthetic during surgery and modified rehabilitation protocols to shorten recovery. Just changing peri-operative pain management alone, can reduce the length of a hospital stay, and facilitate patient to achieve certain benchmarks such as walking with a cane or being independent on stairs much sooner. I am a strong supporter to partial knee replacements as they are a less invasive solution. I believe that the only way to increase the total numbers of UKAs in the US is to better educate residents and fellows and to teach practicing surgeons how to do partial knee replacements. If a surgeon is not comfortable performing partial knee replacement it will not be an option for the patient and a total knee replacement will be performed.
Knee1: As a result of the advances in partial knee replacements, have knee replacements become applicable to a wider range of conditions, or are they simply a last-resort for patients?
Dr. Fitz: I don’t think the total numbers of knee replacements have increased. Most patients in the need of surgery have friends or neighbors telling them how painful surgery is, and how long recovery would take after a traditional total knee replacement. Very few patients have experienced newer methods, or were exposed to the possibility of receiving a partial knee replacement. With more patients undergoing these newer procedures and different peri-operative pain protocols more patients will experience a more pleasant and less painful recovery. This may influence their decision making process.
Knee1: Currently you are helping to develop personalized knee implants. Have you begun to see any advantages for patient specific implants in comparison to a general knee replacement?
Dr. Fitz: We don’t know how beneficial this new technology is. It has to be carefully studied. We do believe that better fitting implants reconstruct the knee joint more anatomically and restore joint function more normally, therefore having the potential to improve short and long-term outcome. Patients may have the potential to receive a knee replacement that feels more normal. We have seen that most patients undergoing these personalized implants have a quick recovery, early range of motion, and the ability to walk with a cane within a few days.
Knee1: When is it appropriate to use bone cements in knee replacements?
Dr. Fitz: In general all partial replacements are cemented in the US. There are some non-cemented UKAs on the market in Europe, but their long-term follow-up results are inferior to cemented versions and are less frequently performed. Long-term results of some non-cemented femoral components in TKR are encouraging, but the norm are cemented components. One of the major disadvantages of non-cemented components is the loss of bone stock if the joint replacement fails. Cemented components have the advantage of using small oscillating blades to separate the cement-implant interface, and in my experience the total amount of bone loss is less as compared to non-cemented components.
Knee1: How has your research on the orthopedic applications of nanotechnology improved the efficacy of bone cements?
Dr. Fitz: Unfortunately it has not yet improved the quality of commercially available bone cements. Although, we have demonstrated an improvement of fatigue properties compared to commercially available bone cement, no orthopedic company has licensed our technology. We hope that orthopedic companies will show interest in this technology in the future.
Knee1: What is the trend are going to affect the development and acceptance of knee technology? Which new technologies are likely to be adapted and which procedures are unlikely to become the norm in the future?
Dr. Fitz: This will be more and more influenced by the cost and the evolution of our health care system. The cost of total knee replacement surgery varies in the US between $30,000 and $35,000. Other countries are able to offer the same surgery for much less. Future technologies have to be cost-effective, and with more patients in the need for this surgery, we may have to decrease our overall cost since knee osteoarthritis is an epidemic. More patients want to receive the most sophisticated implant with all the bells and whistles. We may reach a point where our health care providers may pay only a base price for the implant or implant related products. We, as knee surgeons, should also clarify to patients the real improvements in knee replacement surgery as opposed to the marketing aspects of this surgery. Partial knee replacement, as an alternative to total knee replacement, should be available to all patients who have a good indication for this procedure. To do this, we have to change the curriculum of our residency programs, teach surgeons who currently don’t offer this procedure and educate our patients about this option. We also have to promote and support research of partial knee replacement.
Computer assisted surgery, even though it reduces the amount of malpositioned components, will probably not become standard of care. The industry is currently looking into other technologies such as pre-navigated custom molded cutting blocks, which have the potential to shorten surgical time and reduce morbidity such as stress fractures seen after TKA. All major orthopedic companies are currently developing these blocks, which should be available soon after clinical studies prove their values. Robotic assisted surgery is currently performed in some centers to improve the surgical technique of UKAs. This is an interesting technology but the initial capital investment is enormous and may limit its widespread use. Personalized UKAs and personalized bicompartimental (? TKA) are currently being introduced to the market and have the potential to solve major disadvantages of current existing knee systems. Traditional knee systems require bone cuts to fit the implants rather than the implants fit the bones. These personalized implants replace the femoral cartilage and preserve femoral bone. This results not only in restoring the jointline, but in reconstructing the anatomic surfaces and joint kinematics of the knee. Future studies will have to prove the short-term and long-term benefits of this technology. Single-use, pre-navigated cutting blocks and instrumentation have the potential to shorten surgical time, reduce the complexity of surgery, and reduce costs for the hospital. Bicompartmental knee replacements offer a treatment option for patients with femoro-patellar (knee cap) osteoarthritis in combination with osteoarthritis of the medial or lateral tibiofemoral joint, by preserving the anterior cruciate ligament. There is an off-the-shelf ? implant for medial osteoarthritis available with similar bone cuts, and bone loss as compared to a total knee replacement. There is also a personalized implant for medial and lateral OA available preserving the femoral bone stock using a resurfacing technology. Today most of these patients get total knee replacements.
One of the biggest challenges over the next 5 years will be the development of new total knee replacements simulating more normal knee function. Currently, most total knee systems cannot reproduce normal knee kinematics. The knee does not function like a hinge. The motion is much more complex and is a combination of flexion and rotation of shin and thigh bone. When the knee bends backwards the shin bone rotates inwards allowing the medial condyle to stay more or less in the center of its articular tibial surface, while the lateral condyle rolls and glides backwards to allow better flexion. Current systems do not mimic this kinematic pattern, which may be the cause for limited motion after TKA. Rotating platform knees also don’t follow the normal kinematic pattern, since the pivot point is positioned in the center of the tibia and not on the medial side. High-flex knee systems don’t solve this problem, but may add higher loosening rates of the femoral component and result in removing more bone off the posterior condyles. Even though some designs are on the market claiming the prosthetic knee will function more like a normal knee, the surgical technique first has to evolve towards restoring a ligament tensioning more similar to a normal knee.
Last updated: 17-Nov-08