Jess H. Lonner, MD, said robotics could be helpful for unicompartmental knee arthroplasty, as it could simplify the procedure by reducing the number of instruments and eliminating surgical steps.


Published 6/1/2019
Kaitlyn D’Onofrio

Robotic Technology in Unicompartmental Knee Arthroplasty: Early Results Appear Promising

During the AAOS 2019 Annual Meeting, Jess H. Lonner, MD, professor of orthopaedic surgery at the Rothman Orthopaedic Institute and Sidney Kimmel Medical College at Thomas Jefferson University, discussed outcomes associated with robot-assisted unicompartmental knee arthroplasty (UKA) compared to conventional surgery.

“I think there’s a different role for robotics in different procedures,” Dr. Lonner said. UKAs have a 90 percent to 94 percent survivorship at 10–15 years when performed by high-volume surgeons, according to the literature. “In the hands of excellent surgeons, … the results are very good,” he said.

Unfortunately, when looking at international registry and U.S. insurance databases, “[UKAs] will fail at a higher rate than total knee arthroplasties,” Dr. Lonner added. UKAs could fail for a number of reasons, including:

  • pathology/disease
  • patient selection
  • component design
  • polyethylene quality
  • surgeon experience/volume
  • accuracy of implantation
  • soft-tissue balance

Inaccuracy is a significant problem in UKAs. “Even just a few degrees of malalignment” could lead to premature failure, he said.

“Unfortunately, with conventional techniques, even in the hands of expert surgeons, there are a lot of outliers. [About 50 percent] of us are maligning our tibial and femoral components beyond two degrees of the plan,” Dr. Lonner said. “While it doesn’t sound like a lot, and while it’s certainly not a lot of error for total knee replacements, this could be problematic for our unicompartmental knee replacements.”

Robotics could be helpful for UKA, as it could simplify the procedure by reducing the number of instruments and eliminating surgical steps. Robotics is enhancing the accuracy of bone preparation and helping to align the components and achieve soft-tissue balance.

“You hope that with those improvements, we could improve clinical functional results and durability compared to conventional techniques,” Dr. Lonner said. “Indeed, we are starting to see data to support these expectations.”

A number of robotic devices are currently available, with increasing access each year. “At the current time in the United States, there are only two robotic systems approved by the [Food and Drug Administration] for UKAs,” he shared. One is image-free and the other is CT-based. Dr. Lonner also added that 15 percent to 20 percent of UKAs performed in the United States are done with robotic assistance.

Dr. Lonner then shared the results of a 2009 study he coauthored comparing his first 31 robotic UKAs (using the CT-based system) to a matched group of 27 previous, conventional UKAs. “These were cases during the ramp-up stage, where I was very much in the learning curve,” Dr. Lonner recalled.

Jess H. Lonner, MD, said robotics could be helpful for unicompartmental knee arthroplasty, as it could simplify the procedure by reducing the number of instruments and eliminating surgical steps.

“With the manual techniques, we had 2.5 times greater variability in component positioning, and we had significantly more error in tibial component positioning, whether we were looking at coronal alignment or tibial slope,” he said. “We were almost able to eliminate errors in positioning with the robotic technology.”

Since that study, others have been published comparing robotic-assisted and conventional UKAs. “Again, both with CT-based and image-free robotic systems, compared to manual techniques, there’s a significant reduction in error of component positioning, translation, slope, [and] varus/valgus—all of the important parameters that you want to look at,” Dr. Lonner said (Table 1).

In terms of function and survivorship, Dr. Lonner shared the results of a 2018 randomized, controlled trial by Blyth et al., comparing two-year clinical outcomes in 70 robotic and 69 conventional UKAs. All procedures were performed by high-volume UKA surgeons.

The researchers found no significant differences in complications, adverse events, Knee Society Score, Oxford Knee Score (OKS), Forgotten Joint Score (FJA), or visual analog scale (VAS) score. The only exception in functional outcomes was among patients with high preoperative activity levels. Among those patients, the robotic-assisted UKA cohort had significantly better OKS, VAS, and FJS outcomes. After two years, there were two revisions (3 percent) in the manual group and none in the robotic group.

One of the obvious downsides of robotic technology is cost, Dr. Lonner said, including “upfront capital cost and the per-case maintenance and disposal costs, service costs, [and more].” Some robotic UKAs require preoperative CT scan, which is another expense and is often denied by insurance companies. It is also time-consuming and inconvenient for patients and puts them at risk for radiation exposure.

“Certainly, the newer, image-free systems have reduced the exposure to radiation, but with many of the systems that are in use in our hospitals, one CT scan emits the equivalent amount of radiation as 10 chest X-rays,” he said.

There is also a learning curve, although Dr. Lonner said it is “fairly quick” with current systems.

Dr. Lonner concluded that the currently available data on robotic-assisted UKAs are promising, showing positive safety and functional outcomes. However, longer-term follow-up will be necessary to definitively decide whether robotic technology is the future of UKAs.

“We need to look at these patients at longer-term follow-up, and we’ll be able to report back again in the next five to 10 years to prove one way or another whether this technology is beneficial,” Dr. Lonner concluded.

Kaitlyn D’Onofrio is the associate editor for AAOS Now. She can be reached at