Temperature Increases Inside Some Knee ReplacementsKnee joint replacements heat up under certain conditions. In this study Dr. J. W. Pritchett from the University of Washington (Seattle) explores how much the joint warms up compared to healthy joints. He also looks at what causes the increased joint temperature. Too much heat can cause cell death, knee pain, and implant loosening.
People with healthy knees and patients with arthritic knees and joint implants had the temperature inside their knees measured. Some patient had both knees replaced with different types of implants. Eight different prostheses were used in all. Sensors placed just under the skin measured the temperature of the synovial fluid after walking and cycling.
Dr. Pritchett reports only a one-degree increase in temperature in the normal knee after walking. Arthritic knees and some implants had a two- to three-degree increase. The rotating hinge knee replacement had the greatest increase in temperature (seven to nine degrees). This study also showed that ceramic and metal materials carry the heat away from the bone better than polyethylene (plastic). Titanium implants hold the heat more than prostheses made of cobalt-chromium.
It's not clear how much heat or how long it takes before the heat causes a problem. Doctors are concerned because increased heat can cause scarring and bone loss. The result can be knee pain and joint loosening. Long-term studies of increases in joint temperature with different implants are needed to learn more about this problem.
James W. Pritchett, MD. Heat Generated by Knee Prostheses. In Clinical Orthopaedics and Related Research. January 2006. No. 442. Pp. 195-198.
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