Friday, February 23, 1996
Total knee replacements are among the most successful procedures. However, many complications can necessitate revision. Preventing failure of primary total knee joint replacements (TKR) and handling these problems when they do occur were the topics of a Thursday symposium on "Surgical Challenges in Revision Total Knee Replacement."
John N. Insall, MD, New York, N.Y., discussed the mechanisms of TKR failure and elaborated on techniques to prevent failure. Dr. Insall pointed out that failure can be prevented through careful selection of patients, careful selection of prosthetics and excellent surgical techniques. One such technique is the quadricep "snip" for releasing the tight knee without leaving an extension lag. "If you find, after a standard approach, that you are having a problem everting the patella, the snip is a continuation across into the fibers of the vastus separatus," Dr. Insall said. "This very effectively decompresses the extensor mechanism. ItÕs a simple, quick maneuver and it does not leave an extension lag."
Another TKR complication is tissue buildup between the patella and femoral head. Such buildups result from tracking problems, which are avoidable. "Preparation of the patella is often done as an afterthought, and is not done properly as a result," he said. "I believe it is best done by reaming, because in the end it is quicker and more accurate, and you know what bone you've left behind. When you've finished, you need to flex the joint and look at patella tracking to make sure it stays in contact on the medial side." Dr. Insall noted that many physicians focus on bone cuts and neglect the soft tissues, which have a greater impact on healing and can create complications requiring revision. "I think they are the absolute key to reproduceable, successful total knee replacement," Dr. Insall said. "What you put in the knee is important; the bone cuts really don't matter. The soft tissue, that';s what you really need to pay attention to."
When revision is necessary, perhaps the greatest challenge lies in accessing the site. Leo A. Whiteside, MD, St. Louis, Mo., said moving the quadriceps mechanism out of the way is the most difficult challenge.
"You have to get the quad mechanism out of the way, which is not controversial, but how you do that is controversial, although there has been more consensus lately," he said. "My approach to exposure has generally been to use a tubercle osteotomy below the patella because that's a lower tension area."
Dr. Whiteside briefly discussed V-Y plasty, in which the quadricep is resected above the patella down to the joint line. This procedure probably devascularizes the tissue, and Dr. Whiteside does not advocate this procedure or transecting the quadriceps tendon, because although it provides excellent exposure it averages a 4-degree extension lag.
Dr. Whiteside recommends tibial tubercle osteotomy (TTO) as a more straightforward way to access the knee. "I tend to go below the knee because it is a low tension area and provides a nice piece of bone to sew it back to," he said. "This provides excellent anterior exposure of the knee and leaves the main quad tendon intact. I believe that muscle should be left in place. Three wires and the lateral soft tissue attachments hold it down and provide excellent vascular supply to this osteoperiosteal flap."
A slight angulation of the wires, 30 to 45 degrees, helps hold down the flap. Dr. Whiteside recommends an 8-cm section of bone but said he now uses 4- to 5-cm sections because of the risk of tibial fractures with the longer sections.
Another use for this technique is when replacing a long-stem prosthesis in the femur. Removing old cement can be difficult, and sliding the old prosthesis out of the femur is impossible because the stem has blind-ended slots that will not allow the stem to slide out of the cement. "You have excellent medial and lateral colums and can still seed the new implant well into a repaired femur and treat this knee almost as though you hadn't removed an old implant," he said.
||1996 Academy News Index|
Last modified 27/September/1996