Patients with High-Flex Knee Can Do SquatCan a better knee joint replacement be designed? The author of this report thinks so. There is a problem getting full flexion after total knee replacement (TKR). A new implant design tries to address this issue. The high-flex knee implant gives better bend, but more bone must be taken off to do it. This is a problem if the patient needs another operation on the same knee later.
The high-flex design has been on the market for about five years. It's the first knee to allow flexion up to 155 degrees. Other knee implants give patients 110 to 125 degrees of flexion. Daily activities such as walking, climbing stairs, and getting on and off the toilet require about 110 degrees.
Patients who want to kneel for long periods of time, sit cross-legged, or squat need more flexion. The high-flex design makes it possible. This is important for some religious groups and for some jobs. There are problems with this much flexion. The kneecap gets off track more easily. The result is more pain and excess wear. The kneecap can even break or come loose.
Many studies show that the patient's knee motion before a TKR determines the outcome of the surgery. Good motion means a good result after TKR. The patient with poor flexion isn't likely to get full flexion after the implant is put in. The author suggests that the high-flex implant should only be used with patients who have full motion going into surgery. He concludes that a better design is needed that gives full motion to all patients without forfeiting so much bone during surgery. He also envisions an implant that reduces knee pain and instability when the knee is fully bent.
Chitranjan S. Ranawat, MD. Design May Be Counterproductive for Optimizing Flexion after TKR. In Clinical Orthopaedics and Related Research. November 2003. Vol. 416. Pp. 174-176.
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