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Background: The objectives of this study were to determine whether intramedullary reaming increases bone temperature in vivo to a level that is high enough to produce bone necrosis and to determine the influence of the size and the condition of the reamers on the temperature increase.Methods: Bone temperature variations were recorded in vivo during intramedullary tibial reaming in fourteen minipigs. The left tibiae were progressively reamed from 6 to 9 mm. The right tibiae were reamed with only 8 and 9-mm reamers. The variables studied were the initial and final temperature and the increase in the temperature. Two weeks after reaming, the tibiae were removed and studied histologically.Results: Intramedullary reaming produced an average increase (and standard deviation) in bone temperature of 6.9°C ± 4.1°C. The peak temperatures ranged from 34.9°C to 49.4°C. The average maximum bone temperature was 38.1°C ± 2.8°C when the reaming was done progressively from 6 to 9 mm and 41.1°C ± 4.4°C when the reaming was done only with the 8 and 9-mm reamers. The mean increase in the temperature in the second group of animals (8.2°C ± 4.3°C) was greater than that in the first group (5.4°C ± 3.5°C). Reaming with sharper reamers in the first seven animals resulted in a smaller mean increase in temperature than did reaming with less sharp reamers in the last seven animals (4.6°C compared with 9.2°C; p = 0.001). Histological examination of the tibiae showed periosteal proliferation and an altered disposition of the osteons at the inner cortex with occasional necrotic bone fragments in the medullary canal.Conclusions: Intramedullary reaming in the minipig increased bone temperature. When the reamer initially used was larger than the diameter of the medullary canal and when the reamers were blunted by repeated use, the maximum temperature reached by the bone was higher. This increase in temperature with use of typical medullary reaming techniques did not exceed the limits that would produce bone necrosis.Clinical Relevance: Use of appropriately sized reamers in good condition reduces the increase in bone temperature that occurs during intramedullary reaming.