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Making a Plan for the Perfect Fit: Customizing Knee Implants

To read the full article from VENUE Magazine, click here.

Often when patients visit Beacon Orthopaedics and Sports Medicine for the first time, they are confused or at the very least a little overwhelmed by the many buzzwords they’ve heard regarding knee replacement surgery. They may have heard the terms “robotics,” “computer-assisted,” and “patient-specific” but don’t have a good understanding of what those words mean. As a result, these patients usually enter the office and say something like, “My buddy had his knee done here and was happy with the result, so I’d like to do the same thing he did.”

While the positive referral is great, the “I’ll have what he’s having” mentality doesn’t really work when it comes to determining the best type of knee implant for yourself.

Michael Lawson Swank, M.D., a seasoned orthopedic surgeon with Beacon, has been performing knee replacements for 28 years and computer assisted replacements for over 20 years. He likens the procedure to hanging a picture where you can either do so by eyeballing it or taking precise measurements.

“While it usually works pretty well just eyeballing it, there is less trial and error when you use measurements, stud finders and levels,” says Swank. The same is true when using imaging or some kind of customization in surgery since customization or robotics is like measuring ahead of time.

“Instead of just eyeballing the X-rays and going five degrees or whatever it may be, we measure the patient’s anatomy to know the actual center of the hip, the knee and the ankle to get the correct alignment,” says Swank.

By taking these measurements ahead of time, they are armed with much more information, and this is key because although these are routine procedures, not everyone is built in a routine way. Our bones and bodies are all shaped differently so surgeons have to adjust implants for the patient’s specific anatomy.

“The more experience you have, the better you can overcome that, but if you want to make them as good as you can, it makes sense to gather that information prior to surgery.”

This gathering of information might involve getting a CAT scan or MRI or putting tracers on the bones. It may be a combination of comparing imaging with the information gathered in the bone. Alternatively, the surgeon could get a CAT scan ahead of time and then make a mold like a dentist makes for a crown. They then put that mold on top of the bones to tell them where to cut.

Beyond all this planning, there are also a variety of implants both traditional “off the shelf” ones and custom ones that fit to a patient’s specific bone.

“In knees, we can even use a CT scan to make an implant specifically designed for the patient,” says Swank.

To use the picture-hanging analogy, what makes computer-assisted or navigated surgery different is that surgeons are actually trying to place the picture in the spot where they know it belongs based on the things they can’t see at the time of surgery.

“It’s like we’re trying to hang it on the studs when we can’t see the studs,” says Swank.

The key to improving the entire process, with decreased variability, is to go into surgery with a proper plan.

Think of purchasing a suit. You can either buy one off the rack that will fit decently or you can tailor it for a perfect fit that will not only look better but also feel better. Customizing an off-the-shelf implant is like tailoring a suit from off the rack. To make a fully customized implant is like designing a suit from scratch.

While many surgeons use just one implant, Swank utilizes a variety depending on the patient’s needs.

Swank determines a patient’s need for a custom implant based on their size, shape, profession, activity level, and bone deformity.

The more unusual the shape of the bone, the more likely he is to use a fully customized implant. The same is true for a patient whose age or activity level requires an implant with a proven track record. Furthermore, if Swank is seeing a construction worker, plumber, roofer or carpet layer, someone who puts a lot of wear and tear on their knee, he will use an implant that can spare their ACL.

The fit is so important because if it doesn’t feel right, mobility becomes an issue.

“With knee replacements, patients tend to complain that it feels too tight or too big and just doesn’t feel like the right size,” says Swank. “One of the ways you eliminate those issues is by actually sizing the implant for them.”

Think about getting a dental filling. The dentist can do the procedure, followed by a visual inspection, and all looks good on his end. But until he asks you to bite down to see how everything feels, there is no way to know if everything is just right. Depending on your response, however, the dentist can make slight corrections and you are on your way with a happy mouth. Unfortunately, the same can’t be done during knee implant surgery because your surgeon can’t ask you to walk around in the middle of the operation to check if something feels funny.

“With knee replacements, we want the implant to fit so seamlessly that you forget you had a joint replacement, but you will have a hard time forgetting that if you feel a little off,” says Swank, who can adjust things to one millimeter. “The goal is to get it as close to that as we can because there is a real difference in function.”

The bottom line is that if you don’t think about it if you take your movement for granted, that means it feels normal, and that’s the end goal.

“The idea is to make a plan, execute that plan, then confirm that we executed that plan,” says Swank.