By Jane Ehrhardt
“We’re getting data on things we’ve never been able to measure before,” said Scott Appell, MD, the joint replacement surgeon who performed Birmingham’s first smart total knee replacement (TKR) in Birmingham at Surgical Institute of Alabama.
The world’s first smart knee implant, the Persona IQ, is embedded with sensors and a telemetry system to allow for remote patient monitoring. Produced by Zimmer Biomet, the device automatically measures step count, average walking speed, stride length, and tibial range of motion.
“How much a patient is doing and what kind of progress they’re making on a daily basis is significant,” Appell said. The device collects measurements throughout the day, producing a wellspring of data for surgeons versus reliance on observed data during physical therapy for a few hours a week.
Starting the second day after surgery, the device begins sending the readings. Using Bluetooth, it transmits the data to its home base, which is about the size of a modem stationed in the patient’s home. That securely routes the information to a HIPAA-compliant, cloud-based platform. It does not collect patient locations. The patient’s orthopedic surgeon can then securely access its objective, real-time data. Patients can view everything via a phone app, as well.
The device also sends alerts. “Most of the early alerts so far among my 15 implants are about an abnormally low range of motion,” said Appell, who practices at Grandview Medical Center. “Generally, the cause points to swelling or pain impeding their therapy. We can intervene then to help get the pain level and swelling down so they can get better motion, which is imperative in the early stages of recovery.
“Viewing their own daily metrics has stimulated patients to be more involved in their recovery. We’re a society of instant information, and this is instantaneous. People are fascinated with it. When some of my patients received an alert about their cadence or motion being suboptimal, they said it made them work harder to catch up and keep within the data norms. That early mobilization and early rehabilitation leads to better results, and that’s what this implant allows us to do.”
Early interventions can also help quickly reset the motor pattern that dictates a patient’s gait. “Our brain has a motor pattern it uses for the least painful, most efficient way to walk,” Appell said. “That gait becomes the default setting.”
So as the damaged knee becomes painful, that healthy default setting warps into a limping gait. Post-surgical recovery then requires the patient to consciously reactivate the healthy motor pattern to reestablish their normal gait.
The sensor’s consistent measurements based on actual movement can play an integral role in that recovery. “If we reestablish that default early on—and consistently—then that normal gait happens much sooner,” Appell said. “Intervening early allows you to get back to your normal walking a lot sooner, and that’s where the most benefit is.”
Another advantage to the flow of data straight to the patient’s orthopedic surgeon can mean fewer office visits. “Now you do not have to come to the office to check motion, so visits may not be required for simple things,” Appell said. That can be quite a boon, since most of the 1,500,000 knee-replacement patients each year are not able to drive for about a month. It also spares patients from missing work, finding child care, or having to travel longer stretches to reach their surgeon’s office.
The data flow does not continue forever, though. Daily transmissions last through the first year. The next year, it only sends the metrics for 36 consecutive days every quarter, which drops to annually during the next 10 years or until the battery wears out. That timeline totals slightly over two years’ worth of data.
Appell sees that data becoming even more useful once artificial intelligence becomes part of the assessments. “In 10 years, I think it will look completely different with the millions of data points that can be analyzed in milliseconds with AI,” he said. With the right algorithms, information could be generated about weight-bearing, pain, decay, and positioning, which could advance not just the devices themselves, but the guidance for successfully implanting them for greater patient satisfaction.
“The most unexpected thing about the smart knee replacement has been the verification through fact-based numbers,” Appell said. “Before surgery, the impeded walk and the painful limps are obvious. The view after the implant is a game-changer. To me, it’s how people start walking better almost immediately, and that improvement in the first two weeks post-surgery. I could always see that difference, but now we have numbers. And numbers make everyone more comfortable.”