Stress-Protection After External Fixation on the Intact Rabbit Tibia

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Abstract
Bone loss due to the stress-protecting effect of a metal plate on intact bone is a well-known phenomenon. To determine if a similar effect is caused by external fixation, external mini-fixation was applied on the intact rabbit tibial diaphysis of 1 leg. The other tibia served as control. The animals were sacrificed after 6 or 12 wk, and both tibiae biomechanically tested in 3-point bending. Bone mineral content was measured by photon absorptiometry. No significant changes in bone strength, stiffness or mineral content were found after 6 wk. Strength and stiffness were significantly reduced after 12 wk. Median strength and stiffness at that time were 87 and 88%, respectively, in relation to control bones. Mineral content in the bone segment which had been stabilized by external fixation was significantly reduced after 12 wk (median 90% of values for control bones). No significant change in content occurred at a level in the tibial diaphysis distal to the external fixation device. The stress-protecting effect caused by external mini-fixation on the rabbit tibia occurs later, and is less pronounced, than that caused by metal plates.