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Update For Surgeons on Revision of Knee Joint Replacements

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A knee replacement has become so common any more we tend to forget that it is still major surgery and a fairly complex one at that. With so many aging adults in America, the number of total knee replacements has increased dramatically. And along with that has come the need for revision surgery. Such a second surgery may be done when the implant fails or the patient has knee pain that doesn't go away with exercise.

In this article, surgeons from the American Academy of Orthopaedic Surgeons offer a mini-instructional course on revision surgery for total knee arthroplasty (TKA). Arthroplasty is another name for joint replacement. The title of the article says it all: Revision total knee arthroplasty: What the surgeon needs to know.

As you might imagine, the surgeon can't just go into the operating room and take the old implant out without some serious planning and preparation ahead of time. First, the patient must be examined. Maybe the knee pain isn't really coming from the joint replacement. Knees can hurt when there is a problem up above in the spine, pelvis, or hip and even from down below (ankle).

Of course, there could be a real problem with the implant such as fracture, loosening, or sinking of the device. Infection is always a possibility as is malalignment of the implant and/or of the knee joint.

X-rays, MRIs, CT scans, bone scans and other imaging studies are used to help determine what's going on. But even before that, it's quick and easy (and much less expensive) to do some blood work and/or take a small sample of the fluid from the joint to look for infection.

Sometimes infections can be cleared up with antibiotics but if not, removing the implant may be necessary. If revision surgery is called for (regardless of the reason), the surgeon must go back to the medical records and find out what type of implant was used. The patient's alignment and muscle control must be examined to look for uneven pull on the joint or other problem areas related to bone and soft tissues. These must be corrected during the revision procedure.

Next, the surgeon must decide what surgical technique would be best for each patient. What kind of incision is needed for the intended procedure? A larger incision is required when the surgeon has to clean out the entire joint from infection and get a good look at the condition of the bone. Should the incision be straight or curved? Is more than one incision needed? Can the incision from the first surgery be re-used for the revision surgery?

The authors provide an in-depth examination of these questions and their answers. Specific surgical techniques are discussed in detail with drawings offered and photographs provided that were taken during revision surgery.

Instructions are also covered regarding removal of the implant. Once again, the surgeon doesn't just crack open the knee, remove the implant, and that's it! Each step of the revision procedure has good, better, and best ways to approach it.

Remember, the implant was put into the joint with the intent to stay. It doesn't just pop out. Special surgical tools such as high-speed drills, surgical hammers, and small oscillating saws are used to separate the implant from the bone. Sometimes it's impossible to keep from removing additional bone and that can affect both the revision and the patient's leg length.

The next step is to reconstruct the joint. Taking the implant out is only part of the process. Now the bone is reshaped, bone grafts may be added, bone defects filled in with cement, and a new implant put into place.

Selecting the right implant for the revision requires an additional set of decisions based on analysis of patient factors such as age, condition of the bone, diagnosis, activity level, and so on.

The advantages and disadvantages of each component of the new implant are discussed for the surgeon's consideration. When we say each component, we are referring to both sides of the joint implant: the tibial side (lower half of the joint at the top of the lower leg) and the femoral side (upper half on the thigh side of the knee). Revision surgery may need to remove and replace both component parts.

And there's actually a third piece: the patella or kneecap. It might be possible (and it's actually preferable) to keep the patellar component whenever possible. But if it's cracked, worn, imbalanced, or loose, then it must be removed and replaced as well. And a new patellar component will be chosen that will work well with the new implant.

Throughout the revision process, the surgeon is evaluating joint angles, alignment, muscle balance, leg length, and the need to fill in or augment where there has been an excess loss of bone. The goal is to make sure the joint line (where the two halves of the joint meet) is at the same level on both knees.

Once the implant is inserted, the postoperative process begins. The patient must watch for any signs of infection. Whether infection develops after the first procedure or after the revision procedure, the treatment approach is the same.

First, tests are done to identify what type of organism is growing. The most appropriate antibiotic to combat the infection is selected. If that doesn't work, then surgery is done to clean out the infection (a procedure called debridement) and possibly replacement of the liner that's part of the implant.

After debridement, tntravenous antibiotics are given for six weeks but patients are warned that the success rate is fairly low. That's why revision surgeries are done in the first place. If the revision surgery was required because of infection, then the procedure is slightly different. The implant is removed but the new implant isn't put in until the infection is cleared up completely. A temporary spacer is put in the joint instead and the operation becomes a two-part or staged procedure.

In summary, this review article is as close as it comes to learning everything you ever wanted to know but were afraid to ask about revision total knee arthroplasty. Patients will appreciate how much thought and effort goes into such a procedure. Surgeons will be reminded as well of all the considerations, factors, and hidden variables that must be uncovered and analyzed in the course of the pre-operative planning through to the postoperative phase.

Reference: David J. Jacofsky, MD, et al. Revision Total Knee Arthroplasty: What the Practicing Orthopaedic Surgeon Needs to Know. In The Journal of Bone & Joint Surgery. May 2010. Vol. 92-A. No. 5. Pp. 1282-1292.