Currently looking at a Conformis eye view for a right knee. The first page of the eye view is going to show us various reference points for the tibia. On this page the first image is of the tibial cutting jig. What we’re looking for here is to see how the jig should sit on the bone.
This is something we’ll examine before the procedure, as well as during the procedure, to ensure that the jig is sitting in the right place and that our cuts are as accurate as possible. What helps the seating of this jig oftentimes are osteophytes. So as we examine this image, we’re going to see where the osteophytes on the bone are because we know those are going to be reference points to ensure that the jig is sitting in the proper location.
The next image on the tibial page of the eye view is going to show what the patient’s tibial slope is versus the angle of the slope that we are cutting the bone. So in this instance, the patient’s native slope is 13 degrees and we are cutting at zero degrees. So what’s going to happen is, because 13 degrees is a pretty high slope and we’re cutting at zero, the front or anterior portion of the patient’s cut bone is going to be a lot thicker than the posterior section of the patient’s cut bone.
On the next image we’re looking at the patient’s resection values for the cut bone. After the surgeon makes a cut, he will take this bone to the back table and measure the cut thicknesses at these five points that Conformis provides to see that if the amount of bone that has been removed matches the amount of bone that Conformis recommended be removed. If there are any discrepancies, the adjustments will be made at the time of surgery.
Also on this image, we are going to pay special attention to the LL cut value. LL stands for lowest point lateral. If this number is greater than or equal to 8.5 millimeters, it is not uncommon for the surgeon to do a minus two cuts, meaning take two millimeters less bone, in order to help ensure that we are preserving as much bone as possible all while increasing the odds that we use the finished poly provided.
The next image on the tibial eye view is going to show us the location of the final tibial tray. During the surgery, the surgeon will reference this image to ensure that the implant is seated in the correct location and to ensure that there’s no malrotation of the final implant.
Since the Conformis knee is customized, the implant should match the profile of the patient’s tibia perfectly, or near perfect, helping to reduce any risk of malrotation.
Also on this image, we’re going to take note of the stem drill and keel size. This says it’s 12 millimeters so we will ensure that the 12 millimeter drill and keel are set up before the procedure to ensure a smooth, uninterrupted flow of the surgery.
The final image on the tibial page on the eye view is labeled a medial and lateral offset. So what you’re going to be given here first is the patient’s distal femoral offset. This is going to be different for every patient. In this instance, the lateral side is 1.9 millimeters thicker than the medial side.
So what that means on every patient you’ll be given four polys, the medial sides will always be 6.1, 8.1, 10.1 and 14.1 millimeters. The lateral side is going to be the thickness of the medial side plus the patient’s distal femoral offset, which again, in this instance is 1.9 millimeters. So if the medial side is 6.1 millimeters then the lateral side will be 8 millimeters. And the reason we do this is to ensure that the patient’s knee comes out straight or otherwise known as the neutral mechanical alignment.
The second page of the eye view is going to show the femoral images. The very first image is going to show the positioning of the distal femoral cutting jigs. What we’re looking for here, similar to the tibia, are the locations of the osteophytes that the jig is going to be referencing. We will look at this before the procedure and intraoperatively. Every once in a while, what you might find is that the jig sits pretty well in multiple locations so by utilizing this picture, you can see exactly where the jig should sit to help ensure proper placement and the correct cut values.
The next image is going to show us the thicknesses of the distal femoral cut. So after the surgeon makes his cut, he will take the resected bone to the back table and measure it to make sure that the values are proper. If there are any discrepancies between the actual cut bone and the amount that was supposed to be resected, the surgeon can, at this point, go back and make the necessary adjustments to ensure the proper amount of bone has been resected. The next image is going to show the angle of the distal femoral cut as well as the anterior femoral cut.
The fourth image on the femoral page of the eye view is going to show the three in one block, otherwise known as the F4 block. The important thing here for the surgeon to note is that the medial profile of the F4 shake should line up perfectly with the medial profile of the patient’s bone. This will help ensure proper placement of the jig, as well as achieving the desired cut values.
Conformis will provide the resection thicknesses of the anterior and posterior cuts. After the surgeon makes these cuts, he can take the resected bone to the back table to measure the cut thicknesses, to ensure that the proper amount of bone has been resected. And just as before, if there are any discrepancies, he can go back and make any adjustments that need to be made.
The final section of the femoral page of the eye view is going to show how the implants will look when they are placed in the bone. The first image will show you the back of the knee while the leg is straight. The second image will show you the front of the knee while the knee is bent. The third image will show you how the implants will look from the side while the knee is bent. And the final image will show you the front of the knee while the knee is straight.
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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