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Knee Replacements: What's involved in the operation?

So you've decided you're getting a knee replacement and were just wanted to know what's involved in the operation? Is it a walk in the park? Is it particularly hard? In this blog I'll go through the basic surgical steps involved in replacing a knee. It's all glorified carpentry really!

Step 1: Anesthetics

Usually the operation is done either under general anesthetic or spinal anesthetic. General anesthetic refers to when you are fully asleep. Spinal anesthetic refers to when a needle is placed in your back to numb your legs. With spinal anesthetic you are usually also given some sedation so even though you are technically awake, you don't hear or remember much. Your anesthetist will talk to you about the risks and benefits of each and which may be more suitable for you. In general, if I was having my knee replaced, I'd definitively opt for the spinal anesthetic. Purely because it's a lot more gentle on the body. A knee replacement can be painful, so having that pain come about gently over a few hours (as occurs when a spinal anesthetic slowly wears off) seems a lot more preferable to having all that pain come at once (as can occur when you wake up from a general anesthetic). Also there is a lot less nausea involved with spinal anesthetic.

Step 2: Prepping and Draping

Once anaesthetized we move onto prepping and draping. This involves washing your leg in an antiseptic. We either use a bright pink antiseptic or a dark brown one which often surprises patients when they wake up. The antiseptic kills all the bugs on your skin, of which there are many. The one thing we worry about the most in joint replacement surgery is infection! It can be devastating. Hence we're very careful in making sure everything is covered in antiseptic and that no one touches anything they shouldn't with their dirty little mittens! Once the antiseptic is on, then we drape the leg. This involves getting sterile drapes (often disposable ones these days) and shutting out everything apart from what we need to see, which is basically everything except the knee. Once this is done we all change our gloves, just in case our old gloves were dirty and the operation begins.

Step 3: Incision

The incision for a knee replacement is pretty standard. It's either straight down the middle over the knee cap or slightly to the outer edge of the knee cap. It's usually done with a sharp knife. The knife is changed after going through the skin, as the skin can be considered dirty and we don't want a knife that's touched your skin to also go into the joint. After the skin is cut, we carefully dissect down to the knee joint and enter it. The knee is pretty superficial so this bit doesn't take very long.

Step 4: Inside the knee

Once inside the knee, the first thing we do is get exposure. To do this we release some of the soft tissues around the knee including your ACL and a little bit of your medial collateral ligament so we get good access to the bones.

Step 5: Bone cuts

This is probably the most important part of the operation. Here is where we cut out the arthritic joint using a saw. To know exactly where to cut we use a lot of different systems which I'll go through in another blog. But the basic idea is to make 6 cuts to allow the new knee replacement to go in.

Step 6: Trial components

Once our saw cuts are made then we trial the knee replacement, kind of like try before you buy. We put in what we think is a good "fit" and put your knee through its range of motion. The things we are looking for are stability and tracking. We have to make sure that generally your knee is not too tight, and not too loose and that your kneecap runs right in the middle of the component. It is at this point that we fine tune the soft tissues and bone cuts and prosthesis sizes to make sure we get it as close to perfect as we can

Step 7: Preparation for final components

Then we wash and dry the bones in preparation for the final components. We open up the final components and make sure everything is ready to go and we change our gloves to once again ensure everything is clean

Step 8: Final components

Usually cement is used to implant the components. We put cement on the components and the bone and at that point we have about 8 minutes to put everything in. So it gets a little hectic. We quickly put in the components, making sure we get rid of any excess cement and and making sure the components are in the right place. Once all in, then we breath a sigh of relief and wait for the cement to dry.

Step 9: Final testing and closure

Now we go through the rigmarole of testing the components again and making sure everything is working well. And once happy we close the wound in layers, basically reversing everything we did at the start of the operation. Then we cover the wound up with a waterproof dressing and bandage the whole thing up and then pat ourselves on the back for another job well done!

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