New Way to Prevent and Treat Pain After Knee Replacement

Many people in need of a knee replacement hold off much longer than they should. The reason? They've heard horror stories about how painful the knee will be after surgery. They are told that it's a different kind of pain -- much worse in some ways than the arthritic pain. But in time, the pain will work its way out and they will be able to move pain free once again.

In fact, this bad reputation of postoperative pain after total knee replacement has a large measure of truth. There are many physiologic, biologic, and patient-related reasons for this increased pain. In this article, orthopedic surgeons explain the pain mechanisms and describe a new approach to pain management for this problem.

Why is the pain so much worse after knee joint replacement? First of all, the surgery sets up an alarm in the nervous system that signals to the brain that there is a problem. But the signals that get started amplify and prolong the initial pain until it becomes severe and chronic.

At the same time, the tissues are injured as the surgeon cuts through the skin and removes the old joint. The body responds with an inflammatory cycle that releases many chemicals and substances that have the effect of lowering the pain threshold. That means it takes very little to set off the pain signals and a lot to turn them off. Not only are the cells of the injured tissue reacting, but so are all the pain receptors in the surrounding tissue that hasn't even been touched.

Not everyone has the same pain responses so there must be individual factors at work, too. Some people just perceive greater pain than others when given the same stimulus. This could be a matter of coping skills, the presence of psychologic depression, or the lack of certain enzymes needed to benefit from pain medications.

Studies show that patient-controlled narcotic pain medications work much better than nurse-administered methods. Instead of waiting for the nurse to bring the next dose of pain medication, the patient can decide when it is needed. Staying on top of the pain is a key part of successful pain management. Delaying medication too long can make the pain cycle much worse.

The new pain management protocol proposed by the authors has two parts. The first is called preemptive analgesia. This refers to the fact that it is easier to prevent pain than to try and get rid of it once it starts. Getting control of pain signals in the disrupted soft tissues before those adjacent nerve cells can start firing is important.

The second part is called multimodal analgesia. This refers to the use of a variety of different medications to achieve pain control. Using low doses of several drugs helps turn off the multiple pathways pain messages are relayed to the brain. The best approach is to combine both approaches (preemptive analgesia and multimodal analgesia).

The program begins two days before surgery when patients are started on an antiinflammatory medication. One hour before surgery, a narcotic (e.g., oxycodone) is given. Then during the surgery, the knee is injected with an antiinflammatory and narcotic.

Pain controlling medications and antiinflammatories are continued after surgery. The patient is sent home with pain relievers, sleep aids, and antiinflammatories. Other medications such as Tylenol, gabapentin, clonidine, and ketamine are also used as needed.

Sometimes medications are combined together and injected as one. This is referred to as a drug cocktail. The authors of this article are actively researching various combinations of medications in these cocktails. They are trying to find the most effective combination and just the right dosages of each individual drug. The mixture is injected into all four quarters of the knee (front, each side, back).

Pain levels, pain intensity, and pain duration are used to measure results. Other measures used to assess outcomes include amount of narcotic needed, any sleep disturbance reported, knee range-of-motion, and nausea/vomiting present.

They are finding that the approach reported here is giving superior pain control and much improved functional outcomes. All of this takes some change and cooperation among the many surgical partners. The surgeons, pharmacists, anesthesiologists, nurses, Physical Therapists, and patient/family must work together to create as pain free of a surgical response possible. Communication and collaboration are the key but as the authors put it so well, "the result is worth the effort."

Reference: David F. Dalury, MD, et al. Current and Innovative Pain Management Techniques in Total Knee Arthroplasty. In The Journal of Bone and Joint Surgery. October 19, 2011. Vol. 93-A. No. 20. Pp. 1938-1943.

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