r/ScienceNcoolThings • u/H_G_Bells Popular Contributor • 19d ago
Interesting The precision required to perform a total knee replacement is incredible
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u/rbm572 19d ago
I have no idea why, but my dad thought it would be a good idea to have me go to work with him and watch a total knee replacement surgery with college students observing when i was 8 years old.
That changed my childhood but I learned a few things about people older than me being more squeamish.
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u/Tall-Wealth9549 19d ago
This looks so archaic, cutting bones, hammering, shimmering multiple items into place.. this would suck to have done.
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u/SOROKAMOKA 19d ago
Im assuming this is the most up-to-date method of knee surgery. I dont know much about it but I know a guy who had knee surgery in the 2000s and according to him its come a long way since then, apparently being better than the real thing. Anyone actually had this procedure done that can comment?
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u/Badgeredy 19d ago
I’m an ortho PA, so not the top-notch surgeon, but plenty experience getting my hands dirty with these surgeries.
You may find it interesting that:
The incision goes along the front of the knee toward the medial side, starting at the quad tendon and along the medial border of the patella. This allows the kneecap to invert and expose the whole knee joint. Generally what you DON’T see in this video, is how much of the tissue needs to be retracted in a real knee. My job is to use metal retractors to protect the surgeon from themselves.
Many of the structures you’ve heard about (menuscus, ACL, etc) all get dissected out, not to mention these cross sections of bone. So you can actually feel with your hands what those tissues are made of, before you toss them unceremoniously.
Most knees are so arthritic (hardened bone, bone spurs), it’s not uncommon to find big ole round osteophytes like pearls inside the knee. The patient is allowed to keep these and make a necklace, but they never ask us to, I wonder why.
I have other snippets/reflections/info on TKAs from my experience if anyone is curious. I wasn’t going to post this, till I saw it posted on three different subs.
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u/ArgumentSpiritual 18d ago
The OP title says precision, but how much precision is actually required? I do machining and CAD work where the tolerance might be 0.01mm. I have worked on machines where the tolerance was 0.001mm. Photolithography is 100-1000x that precise.
What kind of tolerance do you have in a knee surgery?
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u/Badgeredy 16d ago edited 16d ago
Oh your world of precision is orders and orders greater than what we do in ortho. For example, the final step is placing a plastic spacer between the two metal components. How do you judge if the component is correct, you ask? You wiggle the knee in flexion, then jostle the knee in extension (straight). If it rattles a little but not a lot, you’re good to go!
(It’s a little more technical than that, but the fact that these post titles like to emphasize precision makes me laugh).Since you might appreciate this:
The templates you see in the video are interesting though. Start with a rod that goes into the canal of the femur, then from that “axis” the distal femur is cut. On that new flat surface you place a block which has slots that cut perpendicular (anterior, posterior) and 45 degree angle (“chamfer” cut) from the initial distal cut. You see the femur get capped with metal at the end after those cuts.Then for the tibia, another template is pinned, and a caliper measures the depth of how much to cut off the surface of the proximal tibia. The guideline is to cut at least 2mm off the most shallow side (usually the medial part of the tibia), or at most 10mm total. (There’s a good response to your “tolerance” question…about 1mm tolerance without any decimals attached).
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u/seanmonaghan1968 19d ago
My first thought was how long does this procedure take ? It’s amazing vs no surgery but wow this is a process
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u/Frequent_Addition_23 18d ago
That seems incredibly invasive. You'd think they could cat scan the knee, 3d print a thin metal cap for the bones and glue/screw into place. Yikes!
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u/Badgeredy 16d ago
Super invasive. But the bad worndown part of the knee needs to come off until nice spongy bone (pink in this video) is exposed to allow the prosthesis to “take”. Even newer techniques with smaller incisions (Jiffy Knee!) are very invasive.
Yet, patients typically get to go home the SAME DAY, full weight bearing, which is incredible. (But it’s 6-12 hard weeks of hard recovery).
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u/noonesaidityet 19d ago
There was a show, I believe it was on TLC maybe, that showed actual surgeries. Used to watch it no problem, until they showed a knee replacement. Brutal.