Surgeons advise healthy skepticism for cementless TKA
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Although total knee arthroplasty has been commonly performed with cemented fixation, research has shown an increase in cementless fixation during the years.
The American Joint Replacement Registry showed cementless fixation was used in more than 14% of primary TKAs in 2020, while the Swedish Knee Arthroplasty Registry and National Joint Registry reported an increase in the use of cementless fixation of 8% and 4.2%, respectively.
Source: Kari Levine
“[Cementless fixation] started back in the 1980s and has evolved significantly over the past several decades because of highly porous materials [and] crosslinked polyethylene so that the results are outstanding compared to the first-generation cementless implants,” Arthur L. Malkani, MD, chief of adult reconstruction and clinical professor in the department of orthopedic surgery at the University of Louisville, told Healio | Orthopedics Today.
Primarily performed in relatively sedentary older patients, the indications for TKA have expanded to include patients aged 65 years and younger. While cemented TKA may provide long-term survivorship in older patients, Geoffrey Westrich, MD, professor of clinical orthopedic surgery at Hospital for Special Surgery, said younger patients had higher revision rates with cemented TKA possibly due to increased activity levels. Previously published research using radiostereometric analysis also has shown that patients who underwent TKA with cemented fixation had stability at 1-year follow-up but implant migration at 10-year follow-up, which is an indication of potential loosening, according to Westrich. He said this differed from patients who underwent TKA with cementless fixation.
“At 1 year, there may be a bit of settling in [with cementless fixation], but [the implants] are rock solid at year 10,” Westrich said.
Evolution of cementless implants
The improvement in durability of cementless TKA implants has to do with the “evolution of porous coating,” according to C. Anderson “Andy” Engh, MD, of the Anderson Orthopedic Clinic.
“We see better porous coating in the form of its 3-dimensional shape, its friction, its similarity to bone in texture and porosity, and then we have the additional additive of a hydroxyapatite-type of coating,” Engh said. “Those were things that were not available in the 80s and 90s – better porosity, better roughness. I do not think we understood back then the value of the addition of keel, spikes or pegs that help with the rotation of an implant.”
In addition to porous titanium and hydroxyapatite coating, which are bioactive materials that enhance osteogenesis and ingrowth, Graham S. Goh, MD, of the department of orthopedic surgery at Boston University Medical Center, said inclusion of a tibial locking mechanism improved stability by reducing the risk of osteolysis found with earlier designs.
“[Previous designs] used screws through the implant and that creates holes, which give an avenue for migration of wear particles, inflammation and osteolysis,” Goh told Healio |Orthopedics Today. “Then the stability between the implant and the bone, because of all the wear particles and inflammation, gets compromised.”
Surgical advantages of cementless TKA include no tourniquet use and about 10 to 15 minutes less time spent in the OR, according to sources.
“Because we do not need to mix cement and we do not need to wait for cement to harden, there is less time on the operating room table and that is always a good thing,” Westrich said. “When we try to make the surgery not take as long, it is less time exposed to anesthesia and potentially less blood loss. And we also know, the longer you are in the operating room, the higher the risk of multiple complications. So, trying to make the surgery more expeditious is always beneficial.”
Patients need good biologic potential
Although cementless TKA may be advantageous for younger patients, sources who spoke with Healio | Orthopedics Today said it may not be amenable for all patients.
“The patients ideal for cementless TKA, in general, are those who have good biologic potential,” Goh said. “This mainly includes younger patients. Historically, it has been aimed at patients aged 60 [years] or younger.”
While poor bone quality may be the main exclusion criterion for cementless TKA for some surgeons, Brett R. Levine, MD, MS, professor of orthopedics at Rush University Medical Center, said it is important to look closely at the indications, which are expanding.
“For me, the indications for doing a cementless knee include a young patient, someone who is 55 [years old] and will need the replacement to last 20 to 30 years. Additionally, patients that desire a physically active lifestyle and those with good bone quality are candidates for cementless TKA. There has been a recent push toward using cementless technology for morbidly obese patients, although this should be determined on a case-by-case basis,” Levine told Healio | Orthopedics Today.
Rate of loosening
Despite the decreased risk of loosening associated with cementless fixation, Goh said the risk of loosening can still occur in the early postoperative period in patients who are younger, more active or who have a high BMI due to increased stress on the component.
“Bony ingrowth usually takes place at least 6 to 12 weeks,” Goh said. “So, the main concern with these newer implants is still the initial stability of fixation before biologic fixation takes place. That is always going to be the disadvantage until we figure out how to enhance and accelerate the osseointegration process.”
Higher levels of early postoperative pain after cementless TKA may be a reason for early revision rates, according to Engh. Although registries have shown higher revision rates with cementless TKA at 1 year or 3 years before leveling off, Engh said registry data do not separate out the reasons for revision.
“In general, young patients have higher revision rates, and we are putting cementless implants in younger patients because we think they have better bone. So, we do not know whether the higher revision rate early on is related to the cementless implant or their age because we are not separating out loosening,” Engh told Healio | Orthopedics Today. “By the same token, men have a higher revision rate than women. And so, when we talk about putting cementless implants in younger males, we have a higher revision rate in younger males because of loosening and infection.”
Surgical considerations
Once biologic fixation occurs, the polyethylene then becomes “the weakest link” of the replacement, according to Levine. However, Levine said as long as the metal remains well-fixed to the bone, replacement of the polyethylene is easy.
“The plastic change surgery is easier than redoing a total knee replacement,” he said. “The procedure is typically a lower level of difficulty, and the recovery is quicker and easier for the patient.”
Levine said another surgical aspect that surgeons should be aware of is that the bone cuts must be more accurate with cementless TKA to achieve adequate fixation. Many surgeons couple robotics with cementless TKA to create smoother bone cuts or create a bone slurry to fill in any imperfections, he said.
“You need to be more careful with cementless TKA and consider techniques, such as cooling the saw blade when you are making your cuts because if you burn the bone, then the bone may not be viable for ingrowth into the implant,” Levine said.
Hybrid fixation
One aspect of cementless implants that has improved is the tibia component, which historically was subject to loosening, according to Westrich.
“We cut a flat surface for the tibia ... and when you put an implant on a flat surface, if you have compressive load on one side, say the medial side, you are going to get a tensile load on the opposite side,” Westrich told Healio | Orthopedics Today. “It is compression on one side but lifting off on the other. If that happens repetitively and there is enough micromotion, you are not going to get any bone ingrowth.”
Westrich said there has been advanced engineering with the tibia component involving 3D printing of titanium that allow for porous ingrowth surfaces that mimic bone and provides initial rigid fixation combined with newer peg and keel designs. Prior to these improvements, Westrich said some surgeons would perform hybrid fixation, which involved cementing the tibia but not the femur because the femur could achieve good fixation. However, as the tibia component improved, he added some companies struggled with identifying non-nickel containing coatings for the femur, which has led to surgeons to cement the femur but not the tibia.
“They are only [cementing] because they do not have the cementless product available,” Westrich said. “The second it is available, they would use it.”
Although published research has shown outcomes of a hybrid implant are similar to those with cemented and cementless implants, sources who spoke with Healio | Orthopedics Today said hybrid fixation is unnecessary.
“I am not a fan of hybrid TKA procedures; certainly, if you are a cementless knee surgeon and you do not like the bone on the tibia, you could do a cementless femur and a cemented tibia. But you are still living with the limitations of how long that cemented implant will last, which was the whole purpose of doing a cementless TKA to begin with,” Levine said.
Future research
As surgeons continue to perform cementless TKA, sources who spoke with Healio | Orthopedics Today said it is important to continue collecting outcomes data through randomized controlled trials.
“Non-biased, non-designer randomized controlled trials comparing cemented to cementless TKA implants in appropriate indicated patients would be a good study with long-term follow-up,” Levine said.
Westrich said studies out to 10, 15 and 20 years comparing cementless knee implants with contemporary cemented knee implants are also going to be needed.
“Those are the kinds of studies that are going to ultimately prove that the longevity of cementless technology is going to be better than cemented knee,” Westrich said. “Then doing those studies in high-risk groups, like high BMI patients and younger, more active patients, are the studies that we are going to need to prove our point.” These higher-risk patients have been studied in the short-term and the results of cementless knee replacements are positive in these patients, but longer follow-up studies are needed, Westrich said.
As future research is conducted, Goh said better definitions need to be established for study cohorts, as well as stricter inclusion criteria.
“What I have seen in other areas of research, not specifically in cementless total knee, are to use ... functional or patient-reported outcome scores that define activity levels preoperatively. I think that would be helpful,” Goh said. “Then having that strict inclusion criteria would give us greater insights on how these modern cementless implants function and how durable they are in active patients.”
Engh said researchers should start identifying the reasons for revision in studies on outcomes for cementless TKA. Because cementless TKA is being indicated for patients who are younger and overweight, Engh said research needs to clarify whether the revision is due to loosening of the implant or other factors, such as infection.
“We will get that data out of the registry when there are enough cementless implants put in that they can start looking at the reason for revision of cementless implants,” Engh said.
Consider risks, benefits
For orthopedic surgeons interested in performing cementless TKA, Engh said it is important to first identify why they are looking to add the procedure to their armamentarium.
“If you are concerned about the speed of your surgery, I probably would not be looking at cementless implants,” Engh said. “If you are concerned about patients with good bone quality, which we generalize to younger males, or patients with high BMI, then that is a reason to look into it and to try it.”
Goh added surgeons also need to consider the risks and benefits of cementless TKA, which include the possibility of early migrations of the implant and the potential requirements of revision surgery in patients who are highly active.
“The literature right now on activity levels is not robust,” Goh said. “Using an age cut off is helpful, but we are not fully certain whether this correlates with activity levels, and the verdict is not out on whether this increased activity and stress on the cementless implant-bone interface is going to be durable in a high-functioning individual.”
Become educated
According to Levine, surgeons who have never performed a cementless TKA should take several courses taught by surgeons experienced in the procedure prior to implementing it in their practice to “get through the nuances of putting in cementless knees.”
“It is a slightly different technique than doing cemented,” Levine said. “It is less forgiving and so knowing the tricks and pearls to avoid the complications, mostly aseptic loosening, would be important.”
When first starting to perform cementless TKA, Westrich said surgeons should perform the surgery on patients with good bone quality who are not considered a difficult case, as well as become familiar with the equipment and how to use the implant.
“Surgeons should try to look at the landscape and figure out which companies have the best track record with cementless knees,” Westrich said. “I would recommend using something that has been on the market for a while that we know is tried-and-true and that does not have failures. I would avoid jumping on the bandwagon of something that is brand new that does not have any good literature on it.”
Monitor patients regularly
Malkani also said surgeons should perform the procedure on a few select patients, monitor them and gradually increase their usage in their patient population as they gain further experience.
“They should monitor these patients’ clinical progress closely,” Malkani said. “That helps provide feedback on how well your technique is and how the patient is doing.”
From a technical standpoint, surgeons should plan the procedure preoperatively and use component sizes that will provide the maximum rim contact at the proximal tibia with the tibial baseplate, according to Malkani.
Although adoption of cementless TKA has been slow due to the high failure rate associated with the first-generation implants, Malkani said the number of cementless TKA procedures being performed will continue to increase and may follow a similar path as cementless total hip arthroplasty in North America as more surgeons become comfortable with the procedure.
“It is good to have healthy skepticism and do it in a prudent fashion,” Malkani said. “For someone who is doing 100% cemented knees, I would not encourage them to do 100% cementless all of a sudden. Be selective in your patient indications, use good surgical technique, choose the right implants and you should have good clinical results.”
- References:
- Chen C, et al. J Orthop Surg Res. 2019;doi:10.1186/s13018-019-1293-8.
- Mont MA, et al. Ann Transl Med. 2017;doi:10.21037/atm.2017.08.20.
- Schwabe MT, et al. J Clin Med. 2022;doi:10.3390/jcm11226608.
- Siddiqi A, et al. Arthroplast Today. 2022;doi:10.1016/j.artd.2022.01.020.
- Uivaraseanu B, et al. Exp Ther Med. 2022;doi:10.3892/etm.2021.10980.
- Wang K, et al. Medicine (Baltimore). 2020;doi:10.1097/MD.0000000000018750.
- For more information:
- C. Anderson “Andy” Engh, MD, of the Anderson Orthopedic Clinic, can be reached at andy@andersonclinic.com.
- Graham S. Goh, MD, of Boston University Medical Center, can be reached at graham.goh@bmc.org.
- Brett R. Levine, MD, MS, of Rush University Medical Center, can be reached at brettlevinemd@gmail.com.
- Arthur L. Malkani, MD, of University of Louisville, can be reached at arthur.malkani@louisville.edu.
- Geoffrey Westrich, MD, of Hospital for Special Surgery, can be reached at carnevalen@hss.edu.
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