Knee replacement surgery types and suggested videos

[Josephine]

People often get confused with the myriad of different terms all coming under the general title of Knee Replacement. I will to my best to explain them here.

They include
PARTIAL (also known as HEMIARTHROPLASTY, UNICOMPARTMENTAL, PATELLOFEMORAL or UNICONDYLAR)

TOTAL REPLACEMENT
~~ CRUCIATE RETAINING
~~ CRUCIATE SACRIFICING
PATELLAR RESURFACING


OTHER TOPICS
MINIMALLY INVASIVE
QUADS TENDON CUT OR 'SNIP'
MOBILE/FIXED BEARING; THE DIFFERENCE
VIDEOS

 

[Josephine]

Partial is a resurfacing of one femoral condyle and the accompanying tibial condyle. In the case of a patellofemoral knee replacement, one femoral condyle and the patella are replaced or resurfaced.

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This is the manufacturer's broken link removed: https://www.biomet.nl/resource/5980/Oxford-Knee-Optec.pdf which is given to the surgeons:
diagrams explain the procedure step by step, more detailed but not as scary as a video.

In a patellofemoral resurfacing, there is metal on the femur and possibly plastic on the patella. Like so

The surgeon may use computer assisted technology to resect (cut) the bone in preparation for the resurfacing.

 

[Josephine]

Total replacement is putting a cap on the entire femur and tibia

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There are two types of this implant: cruciate sparing and the cruciate sacrificing. This is to do with the two strong ligaments that cross over inside the joint and prevent the femur from sliding off the top of the tibia when the knee is flexed. They also control the bones when some rotational movements are made such as in sports like skiing and football.​

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Cruciate sparing
This preserves the cruciate ligaments if they are in good condition. The implants have a notch to accommodate them
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Cruciate sacrificing
When the cruciates are in poor condition or even ruptured, a prosthesis is used which has a peg on the plastic insert and a notch on the femoral component to take over their functions of keeping the joint stable.
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Patellar resurfacing with a button
Sometimes the articular surface of the knee cap is arthritic as well and needs to be resurfaced.
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[Josephine]

Minimally Invasive is the term used when very small incisions are made to carry out the surgery. MIS in hips is keyhole surgery but in knees what most surgeons actually practice nowadays is minimal incision surgery. This simply means that they have realised they can perform the operation just as well through a 6" incision as they can through a 12" incision! Of course, the incision has to be big enough the get the cutting guides and the implants in. These images show an MIS Total Knee Replacement!

What's also included in this definition is the "quad sparing" technique meaning a reduced incision (4" */-, with NO actual muscle cut during the procedure and the patient can therefore expect a relatively easier and less painful experience. However, it should be noted that for the vast majority of surgeons, this is routine and has been for many years. So much so, that few of them no longer define it as MIS surgery and regard it as the standard procedure and therefore hardly worthy of defining. Taking it as read, so to speak.
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But what it means for you, the patient, is that the great muscle the quadriceps, it not interfered with at all. As you can see above, that big white strap of tissue just beneath the surgeon's fingers, is totally intact and the surgeon has just freed it from the adjacent structures so it can be lifted up and aside so he can access the joint.

For those with strong stomachs, this is a real video of an MIS total knee which explains it in much better and greater detail!

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But it has to be said that the size of the leg is an important factor. Small, skinny legs lend themselves much more to this approach than a big leg with a generous layer of fat!

However, partial replacements do sometimes get done with a TRUE MIS as they obviously have much smaller tools and implants.

7" TKR scar 3" PKR scar​

 

[Josephine]

Quads Cut
In order to understand this procedure, it's important to first understand the anatomy and the standard incision.

The quads is the major muscle from the thigh which is attached to the patellar. The structure joining them is the quads tendon. Below the patella it becomes the patellar tendon which is attached to the front and top of the tibia.

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The 'standard' incision commonly used in the skin is the midline incision but deeper inside the knee, it changes to the medial parapatellar approach where the natural cleavage between the patellar ligament and the quads is simply opened up by blunt dissection. This is about as traumatic as it gets!

The so-called "quad snip" is actually just an extension of the parapatellar incision only extended by about 2-3". In the early days (1960-80') it was considered necessary but since then it has fallen out of favour as surgeons realised that it had a very negative effect on the patient's recovery.

The only ligaments that that are really touched are the cruciates if they should be poor quality but that's done as part of the bone removal and a specially designed TKR implant is used to take over their function.

Blunt Dissection
The usual practice in during surgery is to go in between the natural planes of muscles and other structures. This is known as blunt dissection meaning scalpels or scissors are not used to cut through tissues but that they are teased apart with instruments or even fingers. When scissors are used, the closed tips are used to explore those natural planes which are then prised apart by the simple act of opening the scissor points.

There, you never knew that scissors were used not to cut, did you?!



May 23, 2012 - Some Additional Information from our member, Orthodoc:

Most surgeons have adopted some form of the techniques of MIS TKA into their surgery. The instruments and guides are better and smaller than in years past. Overall, the incisions are smaller than they were 10 years ago. However, the marketing of MIS created a need to make the incisions smaller and smaller. In some circumstances this has actually lead to malpositioning of the knee components. Studies have shown slightly quicker recovery times with true MIS, but sometimes at the expense of the final outcome.

As for the terms used in the exposure in knee replacements, take a look at the diagram above. The midvastus and subvastus approach are labelled. These approaches were created as part of the original descriptions of MIS techniques. The blue line is the more traditional approach into the quad tendon, which is still used by a large proportion of surgeons. The red line is the "quad snip." The addition of a quad snip is rarely used as an approach for a primary TKA, but still has its place in the role of revision TKA.

 

[Josephine]

What is the difference between mobile and fixed bearings?

It's just a technicality really.

The mobile bearing is like the DePuy rotating platform where spacer isn't fixed to the tibial component but can rotate around a central pin. You can see the securing pin and the shiny flat platform the plastic spacer moves on both marked. In a fixed bearing the spacer clicks into place in the tibial component, you can see the indent in the bottom metal item where the plastic clicks into place.

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mobile bearing .......................... fixed bearing​

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The theory is that it results in less wear but that really is only a theory.

People often get the impression that this must mean there is more rotation in the mobile bearings than in the fixed bearings. Those who are keen to get back to skiing and such and state that they want a rotating platform because of this. But truth is, the rotation in both fixed and mobile bearings is almost exactly the same!