10 Points on Personalized Knee Replacements

Laura Dyrda -  
The partial and total knee replacement industry has been evolving for the past several decades, with the newest trends toward personalized knee replacements. Studies show that there is no "one-size fits all" knee replacement, and if the surgeon uses an implant that is even slightly too big or too small, the surgery can have a poor outcome, says Gregory Martin, MD, an orthopedic surgeon with Performance Orthopedics of The Palm Beaches in Boynton Beach, Fla.

"While everyone knows that fit can be an issue, and poor fit has been shown in clinical research to have poor outcomes, there aren't a lot of solutions for that right now," says Jong Lee, senior vice president of marketing at ConforMIS. "If you get the right fit in one dimension, you don't in another and you have to live with it." ConforMIS is the first and currently only company in the United States producing personalized knee replacement implants for each individual patient. The kits include implants, instrumentation and cutting guides designed specifically to each patient's anatomy.

"The patient gets a CT scan of the knee and the data is sent to Massachusetts where a model of the knee is made and then the implant and instrumentation is created based on the patient's specific knee anatomy," says Dr. Martin.


1. You only operate on the affected part of the knee.
While partial knee replacements are available, traditionally, the vast majority of piatnes needing a knee replacement got a total knee replacement. This often means the surgery affects the ACL and PCL, says Mr. Lee. However, the personalized knee replacement allows the surgeon to choose a unicompartmental or bicompartmental knee resurfacing implant that preserves the femoral geometry. "The personalized process allows us to look at the patient and the part of the knee that is affected, and then make the implant for the part of the knee that is affected while leaving the rest of the anatomy intact," says Dr. Martin.

2. It's a less invasive procedure.
Using the personalized knee implants is a less invasive procedure than total knee replacement, which means there is dramatically less blood loss, says Dr. Martin. This is advantageous because it allows the patients to become active sooner after surgery and promotes a quicker rehabilitation process.

3. The implant feels like a natural knee.
One of Dr. Martin's patients needed knee surgery in both knees. He performed a total knee replacement in one knee and used the ConforMIS personalized knee replacement in the second knee. The patient reported that the ConforMIS knee felt more natural. "In the end, restoring the anatomy and keeping as much of the anatomy as possible intact makes the knee feel natural," says Dr. Martin.

Performing the procedure

4. Training with personalized knee replacements.
Knee surgeons who are trained to perform total and partial knee replacements can watch web casts, take cadaver courses and visit with surgeons who already perform the procedure to learn the technique appropriately. "It is pretty straight forward and easy to learn," says Dr. Martin. "However, the surgeon should walk into the operation room being able to perform the procedure successfully. They can even do a CT scan for a cadaver knee during the training, which shows surgeons how to implant it in the way it would be in a real OR with a real patient."

There is a network of surgeons across the country available to mentor surgeons who are learning about the procedure. "We highly encourage any surgeon about to do surgery to train in a cadaver workshop and observe another surgeon before performing themselves," says Mr. Lee.

5. How the procedure is performed.
There is a difference between performing total knee replacements with a standard implant and the personalized knee replacement with an individually created implant. "With the standard implant, you are shaping the patient's bone to accommodate an off-the-shelf implant," says Dr. Martin. "There's more bone trauma and soft tissue that needs to be released and balanced. ConforMIS crease implants to fit the patient's anatomy and restore the part of the body that has been lost." The navigation for the procedure is done prior to surgery after the three-dimensional CT scan is taken.

In addition to the instrumentation and implant, the kits include a cutting guide personalized for the patient's knee. Usually, the surgeon starts with a standard cutting guide and then takes the measurements of the individual patient to make sure the implant is put in the right place. "We take away the need for that kind of intraoperative decision making," says Mr. Lee. "We make a guide that is used just for that patient. The surgeon can locate where they need to make the cut right away. Also, because the implant is molded and shaped for the knee, the surgeon needs to make fewer measurements."

6. The whole kit is mailed to the hospital or surgery center.
ConforMIS creates the implant, surgical equipment and cutting guide individually for each patient and then ships the product in a sterilized box to the hospital or surgery center. The equipment doesn't need to be sterilized again before use and is disposable. "It benefits the hospital because it doesn't have sterilization and storage process," says Dr. Martin. "There isn't any difficulty with trays at the last minute. This removes a lot of those concerns and anxiety."

Mr. Lee says the company promotes efficiency for the surgeon and hospital. "When you walk into a total knee replacement, there are usually 8-10 trays of instrumentation that are carted into the room and made ready for surgery," says Mr. Lee. "This all needs sterilization, packaging and storage at the hospital. We ship the kits to the hospital just in time for the surgery. It's really efficient and it makes things a lot easier for the staff and the hospital."

Creating the technology

7. The materials used are similar to other implants.
The personalized knee implants are made from materials that are similar to most implants on the market, such as cobalt. "We use an ultra high molecular polyethylene, which are standard in knee replacement implants for companies," says Mr. Lee.

8. How the implants are designed. Once the company receives the CT scan, the virtual version of the knee is created and the jigs and implant are designed based on the patient's anatomy, says Mr. Lee. "We have invested in an automated design process," says Mr. Lee. "This process speeds the creation of the implant and minimizes the amount of work it takes to produce the implant." The company uses direct digital manufacturing this technology. Using direct digital manufacturing doesn't make sense if the company is creating 10,000 of the same implants in an assembly line. However, it works well for producing one-off items, says Mr. Lee.

The future of knee implants

9. Change is patient-driven.
Patients are savvier about the new types of technologies and procedures because there is more consumer-driven information about these procedures available online and in print publications. "Patients realize that the size of the implant is an issue," says Dr. Martin. When patients decide they want a specific type of procedure, they are able to seek out the closest surgeon who can safely perform that procedure instead of using the surgeon referred to them.

10. More personalization will come.
While total knee replacements are regarded as a viable option, studies show that 20 percent of patients aren't satisfied with their outcomes. Some companies are pushing forward with offering personalized cutting guides, but the implants aren't personalized for the patient's anatomy. There has also been extensive research on gender-specific knee implants, but ConforMIS believes they miss the point. "Gender knees are still based on the notion of using averages, in this case average differences between genders, to design an implant," says Mr. Lee. "But if the idea is that as an industry, we are trying to create implants that are more anatomic, personalization is really the only way to offer that solution."

Learn more about ConforMIS.

Read other coverage on knee surgery:

- Beyond Traditional Surgery: Options for Knee Surgery With Better Outcomes

- AAOS: Internet-Based Rehab Viable After Knee Surgery

- 11 Biggest Sports Medicine Trends for 2011

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