Today, we are going to discuss a Conformis iView for a patients right custom knee replacement. The first page of the iView shows us all of the tibial images that we need. The very first image that we are provided with details the proper location for the T1 tibial cutting jig.
The surgeon will reference this image both preoperatively and intraoperatively. Preoperatively, we are looking for the location of the osteophytes and how they sit on the jig. The osteophytes serve as valuable reference points to ensure that the jig is seated in the proper location.
As the surgeon proceeds with the procedure and he puts this jig on the bone, if he finds that the jig is sitting in multiple places, and there is a question as to which location is best, he can reference this image to ensure that the jig is in the best location for the patient.
The next image is going to show us the patient’s native tibial slope, as well as the slope of the saw blade while making the tibial cut. So in this instance, the patient has a three-degree slope and the slope of the saw blade is going to be zero degrees, so it’s going to be a straight cut.
So if we’re cutting, making a straight cut on a patient with a three-degree slope, then we can expect a smaller amount of bone to be resected from the back of the knee compared to the amount of bone resected from the front of the knee. The next image is going to show what the resected bone will look like, as well as the cut values of the resected bone.
After the surgeon makes his cut, he can take the cut bone to the back table and measure it at the five points that Conformis has provided thicknesses for to confirm that the numbers match. If there is a mismatch between the cut bone and the amount of bone Conformis recommended being removed, the surgeon at this point can go back and make adjustments.
Finally, on this image we want to pay special attention to the LL cuts. LL stands for lowest point lateral. If this number is greater than or equal to seven millimeters, it is often recommended that the surgeon consider making a minus two cut, or taking two millimeters less bone in order to help ensure that we use the thinnest possible polys and help maintain the patient’s native joint line.
The next image is the tibial tray placements. This is going to show us how the patient’s final tibial implant is going to sit on the bone. The surgeon will reference this image to make sure that the implant is placed at the proper location, with the proper rotation, without sacrificing the coverage of the implant.
There should be no overhang of the implant off the bone, and there should not be any significant under coverage. Since this implant is customized to the patient’s unique geometry, the implant should sit near perfect on the bone without any malrotation.
The final image on the tibial side of the implant is the poly section. This section is going to tell us the thickness of each patient’s polys, as well as their native distal femoral offset. In this instance, the offset is 1.6 millimeters.
This means that the polys need to be 1.6 millimeters thicker on the lateral side than on the medial side. So if you have a 6.1 medial poly like you do in this instance, then your lateral poly thickness is going to be a 7.7 millimeters. The surgeon will be given four poly options and he or she may choose the thickness that they feel balances the patient’s ligaments best.
The second page of the Conformis iView contains the femoral images. The very first image is going to show us the placements for the distal femoral cutting block. The surgeon will use this image to ensure that the jigs are pinned in the correct locations before making his cuts.
Once the proper location has been confirmed and the jigs pinned in place, the surgeon will make his distal femoral cuts. He will then take this resected bone to his back table and measure the thicknesses to ensure that the cut bone values matches the cut values that Conformis provided. If there are any discrepancies, the surgeon can make adjustments at this point.
The next image is going to show us the angle of the distal femoral cut, as well as the anterior cut. The next image shows us the placements of the F4, otherwise known as the 3-in-1 block. The important thing to note here is that the medial side of this jig will match with the medial side of the patient’s bone.
So the medial profile of the jig will match the medial profile of the patient’s bone. Once these conditions are met, the jig can be secured in place with pins, and then the surgeon can make his anterior and posterior cuts. After these cuts are made, the resected bone can be taken to the back table to be measured, to ensure that the proper amount of bone has been removed. If there are any discrepancies, the surgeon can make adjustments at this time.
The final set of images is going to show us how the final implant will look inside the patient’s body. The images provided will be with the knee straight, from both the front and the back. One image will show us how the knee will look while the patient’s knee is bent, or flexed, from the front. And then we will also be given one image of how the knee should look from the side.
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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