A Knee Replacement That Talks To Your Doctor? It’s Just The Beginning.

By Peter Loftus

As a ‘smart knee’ that transmits data rolls out, medical specialists and engineers predict sensors will be added to artificial hips, shoulders and spinal implants.

In coming years, your new artificial joints will tell the doctor how they’re doing.

Already, a “smart knee” from medical-device maker Zimmer Biomet Holdings Inc., introduced in 2021, comes with built-in sensors developed by Canary Medical Inc. that can wirelessly transmit a slew of data about how the replacement knee is working.

The details about your gait are sent daily to your orthopedic doctor, who can track your step counts, range of motion and other metrics in the months and years after surgery. Doctors tracking the information can reassure patients who are hitting recovery milestones. Or, if the performance measures fall short, a doctor may intervene to avoid having a patient stuck with an underperforming artificial knee, such as ordering a change in the patient’s physical-therapy regimen.

That’s just the beginning, say doctors and medical-device engineers. They predict sensors will be added to artificial hips, shoulders, and spinal implants. And they envision uses beyond orthopedics, such as tracking whether a brain aneurysm is about to burst, and whether implanted hearing aids or vision devices need to be fine-tuned.

“Using sensors to get data from a patient, you can have thousands of data points to analyze and figure out exatly what’s going on with a patient,” says Edward Harvey, a trauma surgeon and professor of medicine at McGill University in Montreal. Dr. Harvey runs a lab that develops implanted sensors, including one to temporarily assess muscle damage in trauma patients.

Zimmer’s orthopedics rivals are also getting into the market. Johnson & Johnson is developing a sensor-equipped version of its surgical trauma plates, which are implanted devices used to stabilize bone fractures while they’re healing. The “smart plate” could potentially tell a surgeon whether a fracture site is healing, a J&J spokeswoman said.

Some types of implanted medical devices, such as pacemakers and other cardiac devices, have had data-transmission capabilities for years. They can track battery life and features of the device itself, as well as signs of new heart problems in the patient, like heart-rhythm disorders.

But orthopedic implants typically haven’t had such smart features. An artificial knee is implanted in people who have knee pain caused by osteoarthritis, when cartilage thins out and bones converging at the knee grind against each other. Most artificial knees are made of plastic and metal, and are attached to the ends of the thigh, shin and kneecap bones. About one million total knee replacements are performed in the U.S. each year.

Patients undergo physical therapy in the weeks following knee replacements, and are encouraged to gradually become more active to rebuild strength around the new knee.

Doctors usually monitor progress with in-person checkups, patient self-reporting and, if necessary, imaging procedures to gauge how a new joint is functioning. Sometimes that can omit useful information, like whether a patient is taking fewer steps each day than they’re supposed to. Or, patients may simply report incorrect information to the doctor.

“We’ve never had the ability to objectively know how a patient’s truly doing after their surgery,” says Dr. Yair Kissin, an orthopedic surgeon and sports medicine specialist at Hackensack University Medical Center in Hackensack, N.J.

Zimmer, based in Warsaw, Ind., one of the biggest makers of traditional artificial joints, developed its smart knee, Persona IQ, in collaboration with Canary Medical, of Carlsbad, Calif. The sensor device extends about two inches from the end of the tibia portion of the artificial knee. It contains electronics, accelerometers and gyroscopes to track the movement of the knee, and is powered by a battery that can last 10 years or more. The sensors are encased in a cylinder-shaped device that is more than two inches long. When the battery runs out, the artificial knee can function as a standard implant, without data capability.

The sensors transmit data about walking speed, stride length and other metrics via radio waves to a home-base station, a box the size of a small notebook that can be kept on a nightstand. The box connects to a computer.

The information is sent automatically to physicians via an online dashboard, as well as to patients who can track it with an app on their phones. Cadence is displayed as average steps per minute, walking speed is shown as meters per second, and functional range of motion is shown in degrees.

The smart knee generates objective data that doesn’t rely on patients’ memories, says Liane Teplitsky, president of global robotics and technology and data solutions at Zimmer Biomet. And the data transmission requires very little action by the patient because the sensors automatically send data to the base station when nearby.

People who may be exposed to radiation therapy, particularly on their lower limbs, shouldn’t get the smart knee because the radiation can shorten battery life or cause failure of other components, the company says. And height can be a factor in determining good candidates for the smart knee, as the tibia must be long enough to accommodate the sensor extension.

Raymond Schmitt received Persona IQ implants when he got both of his knees replaced last year, three months apart. The 62-year-old from Washington Township, N.J., who recently retired as a letter carrier for the U.S. Postal Service, was experiencing pain in both knees for several years before deciding to get them replaced.

Dr. Kissin of Hackensack University Medical Center recommended Mr. Schmitt receive the new smart knees. He agreed, saying “as long as the knee is put in properly, I don’t care if it’s got a transmitter or not.”

Mr. Schmitt sometimes tracks the data on his phone, but not too often because he knows Dr. Kissin also receives it and would tell him if there was a problem. He said Dr. Kissin has told him during follow-up visits that his metrics are on track.

Dr. Kissin said he noticed that daily step counts and walking distance suddenly declined for one of his patients a few months after surgery. Dr. Kissin called the patient, who said he was just taking a break from his recovery and having a relaxing weekend at home. Dr. Kissin said being able to access the data remotely could spare patients from having to make in-person follow-up visits.

The sensors don’t improve the performance of the artificial knee. Zimmer and Canary caution that the mobility information also isn’t intended to replace clinical decision-making. The data instead are intended as an adjunct to more established ways of gauging knee performance, like seeing how far a patient can bend or extend the leg.

But it is possible that further studies could demonstrate clinical benefits. If, for example, data from the knee signal that a patient can’t bend or extend the new knee as far as expected, a doctor could order a more aggressive physical-therapy regimen. That could help avert a buildup of scar tissue down the line that requires more intensive and costly interventions, says Canary Medical Chief Executive Bill Hunter.

Canary is exploring ways to use machine learning to analyze data and spot signs of trouble. “We can start to give the physicians some sort of early-warning system as to whether or not there’s a problem,” Dr. Hunter says.

It’s possible that the data could inform new algorithms that detect infections, loosening or stiffness of the joint, says Zimmer’s Ms. Teplitsky. Orthopedic surgeons say the ability for a smart knee to detect loosening and infections would be the most useful features of future versions, according to a survey by analysts at Stifel investment bank.

Canary is working on different versions of its sensor device that would fit into artificial hips and shoulders, in partnership with Zimmer, Dr. Hunter says.

“Most every major medical device should provide some sort of feedback to the clinician,” Dr. Hunter says. “Ten years from now, we’ll think it’s crazy that major medical devices didn’t provide any type of feedback to the doctor.”

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