This article is more than 5 years old. Information may no longer be current.
Cementless tibial components make a comeback, but expect slow acceptance
New designs, materials and expanded indications make cementless components a good option.
Click Here to Manage Email Alerts
About 20 years ago, researchers introduced cementless tibial knee components to eliminate third-body wear and to provide long-term durability and fixation.
The popularity of the innovation did not last long, however. High failure rates for some new implants, combined with a dearth of evidence showing any benefits for cementless over cemented implants, caused interest to taper off.
|
Image: Hofmann A. |
Image: Whiteside LA. |
Now only 17% of orthopedic surgeons still use cementless tibial knee components, according to A. Seth Greenwald, DPhil (Oxon), of Lutheran Hospital in Cleveland and an Orthopedics Today editorial board member.
They tend to be the true believers. “There were those surgeons that hooked on to a successful cementless component and they continued to use it over the last 20 years, and they have been ‘disciples’ of cementless fixation,” Aaron A. Hofmann, MD, of Salt Lake City, told Orthopedics Today.
Recently the voices of those disciples became louder. Fueling the resurgence: new materials, better instruments, a better understanding of knee kinematics, expanded indications for total knee arthroplasty (TKA) and improved component designs. The upshot is, in effect, a reintroduction of cementless tibial components.
“It’s about time to get on with it in the knee,” says Leo A. Whiteside, MD, an orthopedist in St. Louis. “Direct bone-ingrowth fixation of implants is effective, tried-and-true technology,” he told Orthopedics Today.
|
Image: Stryker. |
In the 1980s, surgeons recognized a need for cementless components in the knee. “It was clear that bone cement was breaking down and components were becoming loose, and so the idea of biological fixation, which we showed worked in the hip, [was] tried in the knee,” John P. Collier, PhD, of Dartmouth College in Hanover, N.H., told Orthopedics Today.
But while cementless fixation worked well for femoral and patellar components, surgeons were not achieving such good fixation with cementless tibial components. They found early instability and incomplete porous coating that caused wear debris in the prosthesis-bone interface, David S. Hungerford, MD, of Baltimore, told Orthopedics Today.
“The cementless interface is the least stable when it’s implanted and becomes more stable over time as the bone grows into the interface,” he said. “If the mechanical environment is suboptimal so that micromotion is introduced, then … the bone ingrowth phase will occur and you will have a soft tissue interface.”
Cementless components were also more sensitive to minor degrees of malalignment and could experience early aseptic loosening, as compared to cemented components, which achieved peak fixation immediately after implantation, Hungerford said.
Fast time to market
So why did cementless tibial components fail the first time around? Some surgeons point the finger at an untimely rush to the market. “Unfortunately, … TKA was accompanied by massive marketing frenzy, and very little effective and precise engineering was done,” Whiteside said.
Central to those early shortcomings: Fixation of a flat plate on the tibia. “A stem and peripheral pegs, as well as a rigid tray are necessary to fix a flat plate on the cut tibial surface,” Whiteside said. “For some reason, the big companies introduced poorly fixed tibial trays.”
“There were two things that really moved us away from cementless components,” Collier said. “The first was osteolysis on the tibial side, the second was creep of the polyethylene on patellas, and so [there was] separation of the poly component from the metal backing.”
Surgeons turned to using screws and pegs for fixation with the flat tibial components then available. However, when they used screws, backside motion between the polyethylene and tibial trays caused debris that moved through the screw holes and that caused osteolysis.
Whiteside and Hofmann both said that manufacturers introduced poor locking mechanisms for fixation of the polyethylene component, which also caused osteolysis. In addition, Whiteside said, some manufacturers used poorly fused material and gamma-irradiation for polyethylene sterilization. The latter was later found to deteriorate the polyethelene prematurely (a problem later addressed by highly cross-linked versions).
Screws and other variables, such as modularity, may have also tainted the popularity of cementless tibial components.
Tried and true components
Some cementless designs, however, did not cause the osteolysis and polyethylene wear problems. The Ortholoc (Wright Medical Technology), the LCS Complete Rotating Platform Knee (DePuy Orthopaedics) and the Natural-Knee System (Zimmer Inc.) were initially successful and proved durable over the last 20 to 25 years, Hofmann said.
|
|
Images: Collier JP. |
“If you could get good fixation of the tibial component without using screws, it turned out that you didn’t have the osteolysis problem,” Collier said. “If you had a patellar bearing that had a good stress distribution so that you didn’t have the polyethylene creep and pull off the metal backing, you had a satisfactory patellar component.”
Hofmann added that these designs proved that osteointegration lasts with cementless tibial components. “Clearly once you have it in place, it doesn’t go away,” he said. “In fact, it just gets stronger and stronger with time.”
Why the reintroduction?
Expanded TKA indications are one reason that cementless designs are getting a second look. Cemented tibial components tend to loosen in heavier and more active TKA patients and bone-ingrowth fixation with cementless components is more stable.
“Virtually every study of survivorship of cemented total knee shows high failure of the bone-cement interface in heavy, active patients,” Whiteside said. At 10-year follow-up, Hofmann and his colleagues did not find any loosening in patients younger than 50 years old who were treated with cementless components.
New cementless designs now offer better stability, fixation, instrumentation and kinematics than the designs from 20 years ago. “The stability and fixation of the components has dramatically improved over the last 20 years,” Hofmann said. “Components have become better designed … and as we’ve understood the kinematics of the knee the designs of the surface anatomy of the replacement parts have become more anatomic.”
With more understanding of how the knee works, new cementless tibial component designs put less stress on the interface. “Certainly if you have more constrained components, like a hinge, that’s going to put more stress at the interface, and the biologic that happens doesn’t occur immediately,” he said.
New designs meet standards
For cementless implants to be accepted this time around, though, manufacturers and surgeons must adhere to the fixation principles of the bone to the implant and the polyethylene component to the metal tray, Whiteside said.
Collier said that most new designs have a single component tibial bearing that at least initially connects the polyethylene and porous-coated tray. He added: “In some cases there’s no metal tray, there’s simply polyethylene and porous coating. The goal there is to get good fixation and not to have generation of debris at that interface.”
The surgeons agreed that the higher costs for cementless tibial implants is justified and partly offset by savings in operating room time, cement and preparation and delivery.
New developments play a role
New instrumentation and hydroxyapatite (HA) applications are also helping cementless tibial components make a comeback.
Instrumentation, such as slotted cutting guides, is key to the components’ success. In addition to better saw blades and cutting instruments, computer-assisted surgery offers another way for surgeons to check techniques and ensure a perfect cut of the tibia, Hofmann said.
New materials, such as trabecular metal, also aim to improve fixation with cementless tibial components.
|
|
Images: Collier JP. |
In development for the past 20 years, HA coating improves osteointegration without any apparent risks. “Many surgeons will find [HA] attractive for use on the tibia in TKA where they feel insecure with osteointegration technique,” Whiteside said.
Hofmann prefers not to use HA coating for his cementless TKAs, because it could become a third body that causes wear and lysis, and his studies found an insignificant 6% to 7% improvement with the HA coating.
|
Image: Hofmann A. |
Companies now are also recognizing room for improvement and introducing products to improve the HA-coating application. One example: Stryker’s Peri-Apatite. This biologic coating applies HA to the implants while fully covering the three-dimensional ingrowth surface and allowing greater ingrowth. Using plasma spray to apply HA coating only covers the line-of-sight and that could leave parts of the ingrowth surface uncovered, according to a Stryker product manager.
Kirby Hitt, MD, of Scott & White Memorial Hospital in Temple, Texas, recently started using Peri-Apatite for selected TKAs with cementless tibial components, and is seeing results similar to those of cemented tibial components.
“We never had problems getting the implant to fix real well,” he told Orthopedics Today. “It was some of the designs and the backside wear and some of these other issues that led us to think maybe it was the fixation, but it never was. So I think going back to a fixation interface that’s a little cleaner like Peri-Apatite … makes sense to me.”
Resistance from cement users
Despite the benefits of cementless tibial implants, 83% of the orthopedic population continues to use cement – and the migration from cemented to cementless may be slow, Hungerford said.
“The average orthopedic surgeon who is achieving good results with a cemented interface needs to be cautious about making a change from something that’s very successful,” he said. “I think he needs to be shown proof that these new designs and new interfaces actually are producing a very high percentage of demonstrated bone ingrowth and stability.
“It’s not that cemented tibial components are failing in large numbers and we have an urgent situation for which we need a solution.”
Hofmann does not think cementless tibial components will ever reach 100% usage, nor should they.
Rather, surgeons should be selective with their patient population. Patients with poor bone quality may not achieve initial stability with a cementless implant, and older patients with a short lifetime use will perform just as well with the less expensive cemented tibial implants.
“It really is that there’s a place for both techniques,” Hofmann said. “As people get more educated … as they become more comfortable with cementless, we’ll see a much higher usage of cementless components.”