Nuclear magnetic resonance studies of experimentally induced delayed fracture union.

Delayed fracture union was produced in the rat tibia with parenteral administration of prednisolone. Phosphorus nuclear magnetic resonance spectroscopy was used to monitor the local pH changes that occurred at the fracture site throughout repair. During the fracture healing in control animals, the pH of the fracture site changed from 7.2 on Day 2 to 7.5 on Day 20 following fracture, i.e., alkaline with respect to the pH of normal extracellular fluid. Deposition of radioopaque callus occurred mainly during the alkaline phase. In the steroid-treated rats the rate and extent of pH change were significantly less and the fracture site became alkaline five to ten days later than in the control animals. Because radiopaque callus deposition still occurred predominantly in the alkaline phase, union was also delayed by about the same interval of time. The rat prednisolone model differs significantly from the human condition of delayed union. Clinical investigations are indicated to ascertain whether abnormalities of fracture site pH occur in delayed union in humans.