Is there clear evidence that robotic-assisted TKA is more advantageous than standard TKA?

Issue: April 2017

Click here to read the Cover Story, "Robotic-assisted systems may lead to more accurate knee arthroplasty procedures."

Better clinical, functional outcomes

Total knee arthroplasty (TKA) is one of the most clinically successful and cost-effective procedures in medicine, with excellent long-term outcomes. Experiences over the last 20 years from performing mechanical alignment with computer-assisted surgery including navigation, patient-specific instrumentation and standard instrumentation have shown the relationship between reducing malalignment (defined as a hip-knee-ankle angle outside the acceptable range of 180° ± 3°) and improving patient-reported outcomes and implant survival is surprisingly weak and of dubious clinical significance. Hence, although a robotic-assisted technique may improve the ability to hit a preplanned alignment target, one that targets the mechanical axis seems unlikely to outperform standard TKA. More recent studies, however, have shown better clinical and functional outcome scores after mechanical alignment when the limb was left in mild varus and with kinematically aligned TKA in which the target is to restore the native joint lines of the knee. Robotic assistance, which can achieve these objectives in a consistent and repeatable manner, may prove to be superior to standard procedures which have high variability.

Stephen M. Howell, MD — Stephen M. Howell

Robot-assisted surgery has some disadvantages, including the additional surgical time, cost and the lack of versatility intraoperatively when the robotic procedure is abandoned and converted to the use of standard instruments. However, robotic devices other than those currently on the market may emerge which are capable of addressing these limitations. An example of this could be an image-guided, handheld device that accurately drills pins to position cutting guides and thus positions the components in 6° of freedom. Attaching the distal femoral cutting guide to two pins placed on the anterior femur sets flexion-extension, varus-valgus and proximal-distal orientations of the femoral component. Attaching the standard four-in-one chamfer guide to two pins placed on the distal femoral resection sets anterior-posterior, internal-external and medial-lateral orientations of the femoral component. Attaching the standard tibial cutting guide to two pins placed on the anterior tibia sets flexion-extension (slope), varus-valgus and proximal-distal orientations of the tibial component. Attaching the standard tibial rotation guide to two pins properly placed on the proximal femoral resection sets anterior-posterior, internal-external and medial-lateral orientations of the tibial component. Hence, the surgeon can choose his or her preferred alignment method, plan the component positions on a 3-D model made from a preoperative CT scan, have the system determine and guide the placement of the eight pins and use standard instruments and a hand-held saw to execute the plan in a timely and cost-efficient manner. Therefore, a device of this nature, when used in combination with effective alignment techniques, may demonstrate significant advantages over standard TKA procedures.

The widespread adoption of robotic-assisted TKA and hand-held navigation technologies are likely to require non-industry funded, randomized controlled trials. Those technologies that either improve patient-reported outcomes, extend implant survival, reduce surgical time and turn-over or lower costs compared to standard TKA are likely to succeed. Industry should share with hospital systems inventory and instrument costs savings from knowing implant sizes preoperatively.

Stephen M. Howell, MD, is an orthopedic surgeon in Sacramento, Calif.
Disclosure: Howell reports he is a consultant for Zimmer Biomet and THINK Surgical.

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Robotics may reduce inventory, improve work flow

Whether robotic assistance is an important surgical adjunct in knee arthroplasty “depends on what the definition of ‘is’ is,” to paraphrase the 42nd U.S. President. To be clear, I have been a strong advocate for robotic technology for unicompartmental knee arthroplasty (UKA) since before I started using robotics clinically in 2008. Nonetheless, while some data are available to show robotics may be beneficial, we need to continue to track longer-term outcomes to corroborate the published short-term studies and establish whether some or all the measures we are currently using to highlight the value of robotics truly impact function and implant durability.

Yes, in both UKA and TKA, compared to conventional techniques, robotic technology has been shown to optimize the precision of bone preparation and component alignment, reducing outliers and increasing the percentage of components aligned within 2° or 3° of the target. Additionally, in an analysis of thousands of UKAs, robotic preparation is more likely to minimize the polyethylene insert sizes compared to conventional techniques due to more quantified and conservative bone resection. This may eventually prove to enhance durability, since placing the tibial insert on stronger bone has been shown to be biomechanically advantageous. Additionally, using smaller tibial inserts makes ultimate revision to TKA easier and minimizes the need for augments and stems. Finally, soft tissue balance can be quantified through a range of motion in UKA and TKA using the various robotic technologies available. Undoubtedly, accurate soft tissue balance is an important determinant of kinematic performance of the knee after arthroplasty and impacts durability, even in limbs that may seem “malaligned.” Poorly balanced knees are a common reason for early revision and premature failure in both UKA and TKA, so there is tremendous value in having a reliable method to balance soft tissues.

In all fairness, there remains healthy debate about whether the improved accuracy of bone preparation and implant precision makes a clinical difference or has an impact on functional outcomes or longer-term durability. In other words, we do not know for sure whether the precision we desire as robotics advocates is a reasonable surrogate for improved outcomes in knee arthroplasty. Conventional wisdom has been challenged by recent studies that have called into question whether such precision of component or limb alignment in TKA is as critical as we have believed for the past 25 years, as long as the soft tissues are balanced. Regardless of one’s philosophy toward residual limb or component alignment in TKA, having a means to more precisely and predictably achieve some desired alignment and objectively balance the soft tissues is valuable in TKA.

Additionally, while studies of fixed-bearing UKA have found component or limb malposition or malalignment can predispose to failure in UKA, others have refuted the need for extreme precision in UKA, at least when using a mobile-bearing system. On the other hand, several recent studies are demonstrating improved functional outcomes of TKA and UKA with robotic precision compared to conventional techniques and one series has shown improvements in satisfaction and short-term durability with robotics in the hands of several high volume UKA surgeons vs. to published registry data. In an unpublished study, we saw improved durability at a minimum of 2 years after UKA performed by novice users with a robotic sculpting tool compared to large international registries and U.S. payer databases of conventionally performed UKAs. Semi-autonomous robots for UKA have been shown to have a short learning curve that enables even inexperienced surgeons or novice users to perform UKA with precision that seems to challenge inexperienced UKA surgeons using conventional techniques. Given the higher rate of failures of UKA in the hands of low-volume surgeons, an enabling technology such as robotics may prove to be of value.

Furthermore, even if we do not eventually prove an impact on durability or functional outcomes with “optimized” alignment, robotics may prove beneficial if we can show equivalence of outcomes, particularly if by using a robotic tool we can reduce inventory, eliminate instruments and surgical trays, improve work flow and surgical efficiency and show net cost neutrality, or even cut costs. We are beginning to approach the latter goal with newer enabling technologies. Indeed, cost considerations cannot be ignored. In an era of value-driven health care, we are being evaluated by patients, payers, hospitals and regulatory bodies not only based on the optimization of results and avoidance of complications, but also on the cost of care we provide. Mirroring the common trends of innovation in general, newer robotic technologies have recently substantially come down in price. Early-generation systems often required more than 90 cases be performed annually to break even on the investment. Now robotic technology can be profitable in ASCs, which can achieve return on investment after as few as 20 cases per year.

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Finally, we must be able to show these robotic systems are safe and do not put our patients at greater risk for technology-related complications. Several studies by talented surgeons using autonomous robotic technologies have shown an unnecessarily high rate of soft tissue complications, in some cases resulting in the abandonment of robotic programs. On the other hand, our analysis of more than 1,000 consecutive UKAs performed with two semi-autonomous (surgeon-controlled) systems found no soft tissue complications related to the use of robot control. Finally, a distinction should be made between image-based and image-free robotic technologies. One study found that CT used for preoperative mapping with an image-based robotic system exposes patients to a previously unappreciated level of radiation and additional costs can be avoided with alternative methods of preoperative mapping or image-free systems that do not require CT scans.

In conclusion, studies are showing improved accuracy of bone preparation and implant alignment, as well as quantification of soft tissue balance, with robotics in UKA and TKA. Those of us regularly using robotics in UKA believe strongly that precision of component alignment and soft tissue balance are key determinants of longer-term success or failure, and emerging data are beginning to show this to be the case. Data regarding TKA are more scant, owing in part to limited and only recently expanding use of robotics in TKA. Ongoing studies looking at functional outcomes, durability, safety and cost will be needed to prove our efforts in further advancing robot technology are well founded.

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Jess H. Lonner, MD, is an orthopedic surgeon at Rothman Institute in Philadelphia.
Disclosure: Lonner reports he is a consultant for and receives royalties from Zimmer Biomet and Smith & Nephew.