Knee Arthritis: Partial Knee Replacement

Knee Arthritis: Partial Knee Replacement

This surgical demonstration on a right cadaver knee shows a partial knee replacement on the inside of the knee, or medial compartment, for a patient who only has arthritis in that area of the knee. The surgeon removes the damaged cartilage and replaces it with metal surfaces on the thigh bone and shinbone, and a plastic piece in between.

Here is a closer look at a right knee with the incision over the medial compartment to get access inside the joint. The first step is to remove the damaged layer of cartilage on the top of the shinbone. This guide helps the surgeon make the cut at the correct angle. When the surgeon makes the cut with the saw, a small amount of bone is removed as well, making sure a clean surface of bone remains for the new metal implant.

With the knee still bent, the surgeon checks the size of the gap between the 2 bones. Next, the surgeon straightens the knee and checks the gap again. These measurements determine which cutting guides are used next. In this case, a cutting guide that removes 9mm of bone will be used. The guide is put in place and the next bone cut is made. The knee is then bent up again and the next 9mm guide is used.

One final cutting guide is used. These come in different sizes as well and it is matched to the size of the patient. This patient's thigh bone is a size 5. Once in place, 2 holes are drilled through the guide first and then the final cut is made. As a quick recap, the top of the shinbone only got 1 flat bone cut. On the thigh bone, there were 3 bone cuts and 2 holes drilled.

Next, the surgeon places a guide on the top of the shinbone, flat against the bone cut. A triangular hole is punched first and then 2 additional holes are drilled. All of these cuts and holes are made for the new metal surfaces to fit nice and tight. During the surgery on a live patient, a special bone cement is used to make sure the metal surfaces stay in place on the bone.

The metal tray is pressed and tapped into place on the shinbone. Bone cement would also be placed on the back of the metal surface for the thigh bone, then pressed and tapped into place. The final plastic piece is placed between the 2 metal surfaces. The surgeon then moves the knee to make sure everything is working properly, then closes the incision with sutures or staples.

Here is what the partial knee replacement looks like on an x-ray.