Smart implants show promise, but doctors still await clinical evidence
Implantable sensor devices such as smart knees are gradually entering the market, but doctors generally believe that data interpretation and clinical decision support are not yet mature. Zimmer Biomet's Persona IQ has received FDA clearance and is now on sale, but experts point out that converting raw data into diagnostic recommendations still takes time. Industry competition is intensifying, with multiple companies pursuing sensor technology through acquisitions or in-house development, but clinical evidence and cost-effectiveness remain key challenges.
If the knee joint could "speak," who would listen? This is a question orthopedic surgeons and rehabilitation physicians have to consider when faced with a new knee replacement system—one that contains built-in sensors and processors capable of sending joint performance data from deep within the patient's body.
Such devices are becoming part of a growing array of remote monitoring tools, which also include continuous glucose monitors and wearable devices for arrhythmia monitoring. Faced with a flood of data, medical technology companies are still exploring how to make this information genuinely useful to doctors.
"This field is still in its very early stages," said Jay Pandit, a cardiologist and director of digital medicine at the Scripps Research Translational Institute in San Diego. He noted that doctors simply do not have time to review the massive amounts of raw data from wearable devices—and, soon, implantable ones. Pandit added that the data is far from user-friendly, often requiring doctors to arrange for dedicated analysts to review the information on third-party websites. And since most doctors have only 7 to 10 minutes to meet with patients, review medical records, and develop care plans, analyzing large volumes of raw data is not feasible.
Pandit mentioned that enthusiasm for remote patient monitoring devices has grown since the pandemic, but there are currently no unified management guidelines for the data these devices generate.
That hasn't dampened the plans of smart knee manufacturers, however.
"The talking knee is now a reality," Indiana-based Zimmer Biomet announced at last year's meeting of the American Academy of Orthopaedic Surgeons. Just days after receiving de novo clearance from the U.S. Food and Drug Administration (FDA), the company showcased its new knee implant extension featuring embedded sensors.
Now, the smart knee product Persona IQ, developed by Zimmer in collaboration with California-based Canary Medical—a company that manufactures sensors for medical devices—has gone on sale. The product measures a patient's range of motion, step count, stride length, and walking distance, but doctors are not yet sure how to use this data to help patients.
"Moving from 'I have patient data' to 'I can make a diagnosis for the patient' or 'I can tell the patient what they need to do differently' takes time," said Matthew Hepinstall, associate professor of orthopedic surgery at NYU Grossman School of Medicine and co-director of the Center for Computer-Assisted and Robotic Surgery.
In the future, sensors will be able to detect implant problems, help patients adjust their gait, or provide data that predicts patient outcomes. Meanwhile, competitors are developing systems that use wearable sensors to track patient recovery, and they hint that they also have plans for implantable sensors.
Bill Hunter, founder and CEO of Canary, said in an interview that medical technology companies have already launched numerous sensor-equipped devices in other areas. "Getting devices to provide real feedback from inside the body to clinicians makes sense across most major medical devices. I believe you'll see it emerge in various different ways."
Canary Medical designed a hollow stem extension containing a battery, accelerometer, gyroscope, and pedometer to track activity data.Image credit: Courtesy of Canary Medical
What can the data tell us?
Hepinstall said Zimmer's primary challenge is convincing doctors to use the Persona IQ device instead of traditional knee implants. "I'm waiting for wearable sensors to provide enough data and accumulate enough experience to understand how to act on that data before I consider implanting it in my patients," he said. He added that the size of the sensor means surgeons must remove more bone when implanting the smart knee.
Still, Hepinstall said: "Someone has to put these devices in people so we can learn what they can do. Remotely monitoring patients in some way is an important priority." He added that when new types of data emerge, learning how to interpret and apply that information takes time. "Anytime you get new information you didn't have before, it's not necessarily easy at first to figure out how to use it effectively."
The data collected by these smart implants is similar to what is tracked by wearable devices worn on the outside of the knee and connected to smartwatches. Doctors point out that the main differences are cost and compliance—according to a 2016 Gartner survey, about 30% of people stop using wearable devices.
Fred Cushner, chief medical officer at Canary, said that obtaining data on a patient's stride length, gait, and speed can help establish recovery curves to predict how well a patient adapts to the implant. He added that this data could also help doctors understand how to reduce post-replacement pain and how to best position the replacement joint. Cushner was involved in the sensor's development. "You have to do research, but once surgeons start implanting smart knees and the data starts flowing in, everyone tends to believe we can answer some of these unknown questions." Cushner is also an associate professor and orthopedic surgeon at the Hospital for Special Surgery in New York.
He noted that the smart knee is only FDA-cleared for tracking patient activity and is not approved to support clinical decision-making. Data from inside the patient's body could also help scientists design better knees, said Peter Sculco, another associate professor of orthopedic surgery at the Hospital for Special Surgery. "That's an incredible treasure trove of research," said Sculco, who consults for Zimmer but was not involved in the device's development. What excites him about the smart knee? "Being able to compare and contrast the different ways we implant knee replacements—their alignment, balance, the designs we use, the types of plastic we use—and then look at this gait-level data in some way and say, okay, maybe this is a better way to do a knee replacement."
Zimmer confirmed it has plans for more research on the Persona IQ device but did not disclose specifics.
Starting with the knee
As surgeries shift to ambulatory surgery centers and implants are increasingly viewed as commodities, joint replacement manufacturers face rising commercial pressures. "These areas face pricing pressure every year," said Ryan Zimmerman, an analyst at institutional brokerage BTIG. "For companies looking to differentiate, adding smart implant components makes a lot of sense."
Knees are Zimmer's largest revenue source; the company reported knee sales grew 8% in the first quarter of this year and 11% year-over-year in 2021. On a May earnings call, the company declined to comment on whether Persona IQ would materially impact knee business growth this year or next. "I won't talk about the number of hospitals onboarded, but it's significant," Zimmer Chief Operating Officer Ivan Tornos told investors. "The patient pipeline is also significant—beyond our expectations."
Canary Medical's Cushner added that the knee and its implants are also a good place to start using sensors. As Canary develops smaller versions of its sensors, they provide scientists with more "space." In Zimmer's knee, the sensor is attached to a stem that is drilled into the patient's tibia.
2021 Knee Revenue
| Company | 2021 Knee Revenue |
|---|---|
| Zimmer Biomet | $2.65 billion |
| Stryker | $1.85 billion |
| Johnson & Johnson | $1.33 billion |
| Smith & Nephew | $876 million |
Source: Annual earnings reports
The cyborg revolution
Liane Teplitsky, president of global robotics, technology, and data solutions at Zimmer, said the smart knee is part of Zimmer's broader strategy to enhance its products through its own robotics and technology. She said the sensor works much like a pacemaker. "Information automatically downloads to a base station in the patient's home and then uploads to the cloud." Surgeons can use HoloLens smart glasses (made by Microsoft) to guide instrument assembly, and when implanting the knee during surgery, Zimmer's surgical robot provides assistance and collects data.
The smart knee connects to an iPhone app called Mymobility, which pulls kinematic data from the implant as well as data from the patient's Apple Watch to track post-operative exercises. "Everything we're now thinking about bringing to market will generate data or collect data," Teplitsky said. Eventually, Zimmer will use sensors in more implants, including cementless knees and shoulders. Canary Medical has filed sensor patents for heart valves, spinal implants, and stent grafts.
Zimmer is also using data from the Mymobility app to power a feature called WalkAI, designed to predict which patients may experience slow gait within 90 days after hip or knee surgery. The company would need FDA clearance to use this data to make care recommendations. "You can go from predictive capability to recommending capability," Teplitsky said. "That's still in the future. We can't make any claims today, but that's ultimately the goal."
A view of the physician dashboard for Zimmer Biomet's Mymobility system.Image credit: Courtesy of Zimmer Biomet
Other companies target sensors
Zimmer's competitors have not yet launched their own smart knee implants, but they are betting on the need for data, primarily through wearable devices. Stryker, the second-largest knee manufacturer by revenue, acquired OrthoSensor last year; its technology is integrated into knee implants to help surgeons balance the knee during surgery. Both Zimmer and Smith & Nephew, the fourth-largest knee manufacturer, have used OrthoSensor's technology in their knee replacement systems.
Stryker also uses OrthoSensor's wearable sensors, which attach above and below the patient's knee to track range of motion, gait, and other information before and after surgery. "It's all about information that the surgeon can use for every unique patient. Its applications certainly include capturing short-term baseline information pre-operatively and monitoring up to 90 days post-operatively to truly see progress," said Don Payerle, president of Stryker's joint replacement division.
Richard Newitter, an analyst at financial services firm Truist, said Stryker will likely also begin adding sensors to its implant products. Shagun Singh, an analyst at RBC Capital Markets, said Johnson & Johnson is also developing smart implants. "They've said they have over 50% share in the trauma market, so they want to enter that market first," Singh said.
Looking ahead
Truist's Newitter said the technology may still be in its infancy, but sensors that allow patients and doctors to monitor health and improve outcomes have become "an important area of focus and development" in the medical device industry. "It's no longer just about the implant itself—it's about building a complete digital ecosystem around the entire care process of the surgery," Newitter said.
Of course, sensors come at a cost. RBC's Singh noted that Zimmer prices its sensor-equipped implant at $1,000 more than the version without sensors. Newitter said it may take several more years to accumulate enough data to prove that sensors improve health outcomes and reduce costs for insurers. "We're interested in whether it will take off like robotics did," said BTIG's Zimmerman. If it does, "you should see many other companies follow suit," Zimmerman added.