Today I will be talking about the ConforMIS iview for this custom knee replacement. The current iview I am looking at is from a right knee. The iview consists of two pages. The first page is the tibial side of the procedure. The second page is for the femoral side of the procedure.
On the first page, the first tibial image that we are provided shows us the location of the very first jig, which is the tibial cutting jig. While the surgeon is operating, he will reference this image to ensure that his tibial jig is in the correct location.
The next image that we are going to look at is the patient’s native slope compared to the slope that we will be making a resection, compared to the slope angle that we will be making our resection at. In this instance, the patient’s native slope is seven degrees and the slope of the tibial cut will be a straight cut, zero degrees.
So what we can expect from that then is to have a higher value or thicker bone cut from the front and as the cut proceeds posteriorly to the back, the cut value will get thinner and thinner. And that is because of the patient’s native seven degrees slope versus a zero degree cut value.
The next image is going to show us the cut values at five, or cut thicknesses at five different reference points along the tibia. After the surgeon makes his cuts, he can take this resected bone to his back table and measure the thicknesses at these five locations to make sure that the amount of bone that has been resected matches the amount of bony resection ConforMIS had recommended.
If there are any discrepancies, the surgeon can make adjustments at this point. One other piece of information we are going to look at on this image is the LL value. LL stands for lowest point on the lateral plateau. If this number is greater than or equal to seven millimeters, it is not uncommon for the surgeon to take two millimeters less bone, meaning a slightly thinner cut.
This will be based on how tight or loose the knee feels. The next image is going to show us the placements of the final tibial implant. This image is important because we want to ensure that the tibial implant is put in at the correct rotation, as well as ensuring that there is no significant under coverage or overhanging of the implant to the bone.
Also in this image, you will be told what the stem drill and keel size is. There are three options. Either 10 millimeters, 12 millimeters or 14 millimeters. In this one, the patients stem drill and keel size is 14 millimeters. Usually, always, if a patient’s keel size is 14 millimeters, then we know this is going to be a very large knee, which tend to be a little more difficult to work with.
We can expect harder bone and spending a little extra time fine tuning our cuts to make sure that they match the values provided by ConforMIS. The last image on the tibial page of the iview is going to show us what the patient’s distal femoral offset value is.
And in this instance, the lateral side of the patient’s distal femur, excuse me, on this particular patient, the patient’s distal femoral offset is going to be 1.6 millimeters. This means that the lateral side of the poly needs to be 1.6 millimeters thicker than the medial side of the poly in order to achieve a neutral mechanical alignment.
In other words, this is the required poly’s thicknesses in order to ensure a straight knee. Each knee will come with four polys on the medial side, it will always be 6.1 millimeters, 8.1 millimeters, 10.1 millimeters and 14.1 millimeters. And the lateral side will be the same thickness as the medial side plus the patient’s distal femoral offset, which again, in this case is 1.6 millimeters. So a 6.1 millimeter medial poly will have a 7.7 millimeter thickness on the lateral side. That’s 6.1 plus 1.6 millimeters.
The next page of the iview will provide valuable information on the femoral side of the procedure. The very first image is going to show us the proper placement of the distal femoral cutting block. The surgeon will frequently reference this image to ensure that the jig is placed in the proper location of the bone. The next image is going to show us the cut values for the distal femoral implant.
After the surgeon makes his resection, he can take the cut bone to his back table and measure the thickness of the cut bone compared to the resection values that ConforMIS provided. If there is any discrepancy between how much bone has been removed compared to how much ConforMIS said should be removed, the surgeon can go back to this jig and make the adjustments necessary in order to ensure a adequate cut value.
The next image is going to show the angle of the distal femoral cut, which is in this instance five degrees, as well as the soon to be made anterior cut, which for this patient is 10 degrees. The next image shows the F4 block otherwise known as the three in one cutting guide.
It is important to know that the medial profile of this cutting block or ijig should match the medial profile of the patient’s medial femoral cut bone, excuse me. It is important to note that the medial side of this F4 cutting jig should match the medial profile of the patient’s femoral bone. This helps ensure proper placement of the jig.
Once the proper position has been found, the jig can be pinned into place and the surgeon can then make his anterior and posterior cuts. After these cuts have been made, the surgeon can take the cut bone to his back table to measure the cut values and compare the amount of bone removed compared to the amount of bone ConforMIS recommended be removed. If the initial cuts did not remove enough bone, the surgeon can go back and make adjustments to ensure that the cut values…
After the surgeon has made his anterior and posterior femoral condylar cuts, the surgeon can then take this resected bone to his back table and measure the cut thicknesses. If the amount of bone that has been resected does not match the amount of bone ConforMIS recommended be resected, then the surgeon can go back to this jig and make the necessary adjustments in order to ensure the proper amount of bone has been removed.
The final set of images on this iview show how the final implant is going to look after the procedure has been completed. The images provided will show the appearance of the knee while the leg is straight from both the front and the back. We will also get a view of the front of the knee while the knee is bent or flexed at 90 degrees. We will also get a view of the side of the knee as it is flexed to 90 degrees.
I am fellowship trained in joint replacement surgery, metabolic bone disorders, sports medicine and trauma. I specialize in total hip and knee replacements, and I have personally written most of the content on this page.
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