New Knee Tech

Orthopedic surgeons bring advanced tools to the OR.

After Craig Hageman heard a webinar by Dr. James Kohler, he knew this was the surgeon his knees needed.

Kohler, a McFarland Clinic orthopedic surgeon, performs total knee replacement the traditional way as well as with advanced robotic technology recently acquired by Mary Greeley. (Kohler practices at the medical center and the Ames Surgery Center, but all robotic surgeries are done at Mary Greeley.)

The robotic device is called the ROSA system. Kohler uses pre-operative X-rays detailing a patient’s measurements to create a 3D image of that person’s knee. Based on this 3D image, the device creates a custom blueprint for optimal alignment, joint stability, and mobility. The software helps the surgeon determine the ideal positioning of the implant, ensuring the best possible fit in the surrounding soft tissue and customizing alignment and balance through a complete range of motion.

After the surgical site is exposed during the procedure, optical trackers and a mini camera are attached to the patient. Real-time images are sent to a computer monitor, so the computer always knows exactly where the knee joint is in space. ROSA acts like a GPS system, adjusting for the tiniest movement.

The computer images provide Kohler with a continuous flow of data that aids in each step of the procedure. While Kohler cuts the bone and places the implant, the device’s robotic arm helps ensure precision of the cut and placement.

Manual knee replacement relies on a lot of external guides and jigs, notes Kohler. There are clamps around the ankles, and the hip’s location is based on various external landmarks derived from population averages.

“With robotic knee replacement, we're able to register a lot of different data points in the knee, but also at the ankle and at the hip, to really get a good plan of what the limb alignment is on a computer screen with a lot more detail than what we get with traditional, manual instruments. It gives us a lot more patient-specific information about their alignment that we use to determine how to execute the knee replacement,” he says.

Bad Knees

Hageman, who is in his 70s, describes the deterioration of his knees as “the culmination of lots of things: sports injuries from high school, age, and the onset of osteoarthritis.” He had trouble with mobility, standing from a sitting position, getting in and out of his car, and going upstairs.

“Just about every daily task was difficult. I’d grit my teeth and get through it every day,” he says. “My quality of life was at a point where I kept thinking what it would be like a year from now without surgery.”

After hearing the webinar on treatment options for arthritis of the knee and hip in June 2025, Hageman got a referral through his primary care physician and was able to schedule an appointment with Kohler within a week. (The webinar was offered through Mary Greeley’s Prime Time Alive program. A recording of the presentation is available at: mgmc.org/kohlerwebinar)

“I have an interest in the medical field and cutting-edge technology, so hearing about advancements and improvements captures my attention,” says Hageman.

Hageman played football and baseball as an Ames High School student and was a runner and fast-pitch softball player as an adult. Dr. Kohler also is an Ames High graduate and student athlete, so there was a quick connection for the two men.

Hageman was familiar with robotic surgery, having had a radical prostatectomy in 2013 performed by Dr. Damon Dyche, a McFarland Clinic urologist, with the da Vinci surgical robot at Mary Greeley.

The da Vinci robot, which many people are familiar with, is used for minimally invasive surgery and involves a surgeon manipulating surgical instruments from a console near the patient. The ROSA device operates differently. It is no less invasive than a traditional knee replacement surgery, and Kohler is at the patient’s side during the entire procedure.

“The saw is always in my hand. There's never a point where a robot is autonomously doing anything to the patient,” he says. “It's really used to help navigate and achieve a precise cut and implant position, and all those things that we strive for.”

Robot Benefits

There is greater awareness of robotic surgery, and it isn’t unusual for a patient to bring it up with Kohler.

“I let the patient make that decision," he says. Some patients have had family members or experience, or even if it's as simple as having read something online, if they have some kind of notion or thought about robotic knee replacement, I think, rather than trying to steer away from that, we have it available, we use it, people do really well with it. It’s still a new tool in our hospital, but its utilization is growing as we continue to expand its use for more patients.”

Traditional and robotic knee surgeries can both have great outcomes, says Kohler. There are situations “when robotic is definitely the right answer, such as when there's deformity or there is hardware in place that makes use of manual instruments challenging. Having a platform available to use when those patients arise is critical but also having it available to supplement manual knee replacements—being able to comfortably do both is really important for me.”

The key benefit, ultimately, is the patient-specific, real-time information Kohler has while he is performing a procedure.

“We get feedback from the screen and from the information generated by what we're doing. So, every cut we make in the bone, it's showing us how much bone we resected. Did we re-sect the amount that we wanted to?” he explains. “And then when we use temporary trial implants to really dial in the size and position of the implants, on the screen I'm able to see what changes in the limb we have made. If it was 10 degrees varus (bow-legged) and we put in our trials and we've dropped that number closer to zero, that tells me we've done a good job restoring the leg to being straight.”

The same applies with people who have contracture, or rigid tightening of muscles, tendons, or tissues, he says.

“For people that have really bad, stiff knees that maybe don't bend well or don't get straight, we can objectively measure how many degrees short of straight they are. And then with our trials and with our final implants, we're able to objectively know that we got this leg to zero degrees, which is perfectly straight, and it bends to 135 degrees, which is really good motion with a knee replacement."

Hageman notes that due to the condition of his knees, his legs were bowing. Surgery has made them “incredibly straighter,” he says.

Meanwhile, his recovery has gone well, and he’s developed a strong commitment to physical therapy.

“I didn’t go into surgery with blinders on,” he said. “I knew recovery was significant and I was encouraged by friends and family to do physical therapy. I’m now a true believer that physical therapy goes hand in hand with recovery.” ■

Smarter Knee Surgery

Dr. Michael Stefl wears an Arvis headset, which helps him accurately align cuts and place knee implants.

With his headgear on, you might think Dr. Michael Stefl is preparing for a virtual reality game.

In reality, the McFarland Clinic orthopedic surgeon is using one of the most advanced tools available for total knee replacements at Mary Greeley: augmented reality surgery.

The device, called Arvis, is a wearable augmented reality system that provides real time guidance during joint replacement procedures.

“It’s a great tool to make us more efficient and achieve reproducible outcomes,” Stefl says.

Once the surgical site is exposed, trackers attached to the patient send data directly to Stefl’s headset. The system’s screens appear in his natural line of sight, so he simultaneously sees both the patient and the digital overlays.

“Since you’re getting an expanded picture of the patient’s anatomy, the surgeon has more flexibility to adapt and fine-tune,” Stefl explains. “I’m still making all the decisions, but the perspective you’re getting helps you make those decisions quickly and effectively for the benefit of the patient.”

A tracked stylus allows Stefl to register key anatomical landmarks such as the knee center or femoral axis. This creates a detailed, individualized 3D map of the patient’s anatomy, which the system uses to guide bone cuts and implant positioning. The headset’s tracking cameras monitor the stylus and other instruments to ensure accuracy and alignment throughout the procedure.

This quick, precise mapping helps streamline the workflow and can shorten surgical time, especially in cases involving deformities or previous surgeries where anatomy may be more complex.

Stefl currently uses the system for total knee replacements, but he anticipates incorporating it into hip replacement surgery in the future as the technology continues to evolve.