High-resolution phosphorus nuclear magnetic resonance spectroscopy was used to monitor noninvasively the local pH changes that occur in vivo throughout fracture repair in rats. During the healing of a fractured shaft of tibia, the pH of the fracture hematoma changed from 7.2 on day two to 7.5 on day 20, i.e. alkaline with respect to the pH of normal extracellular fluid. This did not occur in a hematoma created by the direct injection of blood. Deposition of radioopaque callus occurred mainly during the alkaline phase. Abnormalities in the control of local pH may be important in the etiology of delayed union, and future forms of local therapy may be usefully directed toward influencing this parameter.
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