Thermally induced bone necrosis in rabbits. Relation to implant failure in humans.

The exposure of bone to high temperatures has become quite common, especially with the increasing use of polymethylmethacrylate (PMMA) bone cement. With particular regard to total hip arthroplasty, many authors have commented on the temperature problem induced by the curing PMMA cement mass. Polymerization temperatures at the bone-cement interface have been measured and range between 40 degrees and 110 degrees, depending on the thickness of the cement line. Thermal bone damage is implicated as a significant cause of early loosening of implanted joint prostheses. The authors designed a fluid probe to deliver heated isotonic fluid directly over exposed cortical bone on a rabbit's proximal tibia. Scald temperatures ranged from 45 degrees-90 degrees for a standard exposure time of one minute. Bone tissue samples taken at intervals of one, two, and three weeks postoperatively were used to establish the thermal-damage threshold for living bone and assess regeneration potential. Controls were included to observe the reaction of bone to the surgical procedure. Bone necrosis was consistently seen in histologic sections at scald temperatures greater than or equal to 70 degrees. Although an inflammatory reaction replaced by a fibrous tissue scar was seen at the site of surgically damaged periosteum, no control animals showed evidence of either bone or marrow necrosis. These results led the authors to suggest that joint replacement systems in human bone, using PMMA bone cement, be designed to limit intraoperative temperature maximums to a level less than 70 degrees. By preventing excessive bone necrosis at the bone-cement interface, early loosening and subsequent implant failure may be significantly reduced.