Abstract
The simultaneous measurement of tracer resorption and apposition in a rat fracture model was accomplished with 99mTc labeled methylene diphosphonate ( 99mTc-MDP) and 125I labeled phenylphosphonic acid ( 125I-øPA), respectively. Loss of 125I-øPA from the fracture site showed a biexponential release pattern; I = 31% ( t 1 2b = 2.0 d ) and II = 69% ( t 1 2b = 55.4 d ). 99mTc MDP temporal apposition at the fracture site followed the law of allometric growth ( y = bx k ) with k = 7.75, 10 days post injury. The 125I-øPA loss differed significantly ( P < 0.001) when compared to normal bone which exhibits a monoexponential release with a t 1 2b = 962 days. In the rat tibia fracture model investigated, bone apposition significantly ( P < 0.001) dominates over bone resorption as a function of time. This overwhelming difference partially accounts for the healing process. The apposition-resorption comparison may be a useful index for following the course of skeletal pathology for a variety of model systems.
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