Dr. Waldman: We know that about one in five patients are fairly unhappy with their knee replacement, even when the x-rays look perfect and the surgeon feels that it came out very well. One of the reasons that happens is probably because off-the shelf implants don’t fit perfectly. They either overhang, meaning they rub on the soft tissues, or they’re too small and the bone sticks out. And, the closer we can get those parts to fitting their knee, we think the happier the patient’s going to be and the more natural it’s going to feel.
How does ConforMIS compare to off-the-shelf implants when trying to maintain the joint line?
Dr. Waldman: Maintaining the joint line is one of the most important things. With offthe-shelf implants, we use a number of jigs and alignment guides to try to estimate where that joint line should be. But even in that case, we’re still approximating what that surface should look like. The bearing surfaces are often fairly flat and fairly straight across the knee, which is not the case in normal anatomy. The lateral side is higher than the medial side. The curves are different on either side. The bearing surfaces are different widths and different heights, and we can’t replicate that out with an off-theshelf implant. With the ConforMIS knee, the computer can calculate out exactly where those bearing surfaces should be, the correct radius of curvature and the correct difference between the medial and lateral side. One of the really interesting things that we see when we get the actual implant is that there is a step-off between that medial and lateral side, which mirrors the patient’s real anatomy. And in some patients, it’s actually straight across, and in other patients it’s as much as 4 or 5 millimeters difference, and it’s different on every patient.
How does ConforMIS compare to off-the-shelf implants when trying to achieve correct rotational alignment of the femoral and tibial components?
Dr. Waldman: One of the crucial steps in knee replacement is to rotate the femoral component. So, we have to externally rotate it to make sure that the kneecap works correctly and that the knee rotates as you bend it. That’s always an approximation with an off-the-shelf knee replacement. We usually just pick one number, say three degrees, and replicate that in all patients. If we try not to use three degrees, we’re using various approximations to try to pick some other number. What the ConforMIS CT scan does is it pre-calculates that number. One of the compromises we always need to make with an off-the-shelf implant is how it fits the tibia. The ConforMIS implant, by matching the patient, covers that bone completely and we found that there’s very little exposed bone on the proximal tibia, which can not only bleed, but is required to support that implant. So, the advantage of covering the whole tibia and having the correct rotation compared to the angle, I believe, it’s crucial.
What is your experience balancing the soft tissue using ConforMIS implants?
Dr. Waldman: One of the questions that surgeons asked me about the ConforMIS knee is how do you do the soft tissue balancing. And what we found is that there actually isn’t much soft tissue balancing to perform. The implants themselves fit so well that the soft tissues often align themselves. They’re back at the correct length. They’re back in the correct alignment. And by putting them right where they should be, we don’t have to do a lot of the balancing that we used to have to do. Second advantage is that because it’s a patient-specific implant, it can be designed to take much less bone out.
You were an early adopter of the ConforMIS technology. What have you noticed with respect to patients’ recovery time using these implants?
Dr. Waldman: It’s very exciting to be one of the first surgeons to be able to use this technology. It’s really benefitted my patients. When patients come back to see us in the office, I’m finding that they are at a much more advanced stage earlier in their recovery time, so patients often see me two weeks to four weeks after the surgery and they often seem as if they’d had the surgery six weeks to 10 weeks ago, because their motion is better, they’re recovering more quickly, they need less narcotics, less pain medication. And in general, they’re just much happier after the surgery.
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