99Technetium bone scanning in experimental osteomyelitis

A rabbit model of experimental osteomyelitis was used in an attempt to clarify the natural history of bone infection associated with positive scintigraphic and negative radiological findings. In this model a pathogenic strain of Staphylococcus aureus is injected in the proximal metaphysis of the tibia of a rabbit, 15 minutes following the injection of a sclerosing agent. Scintigraphies were performed at 3, 5, 12, and 19 days following this procedure; 99m-Technetium phosphate compounds were used indifferently. On days 5, 12, and 19 a roentgenogram of the lower limbs was taken. Animals were sacrificed at random 6, 14, and 21 days following the procedure. Against expectations, the standard radiological procedure was more sensitive than the scintigraphic technique. The probability of finding a positive bone scintigrapy in the presence of osteomyelitis P(S+/O+) was 15/19 or 0.78. For the roentgenograms P(X+/O+) = 16/17 = 0.94. On pathological review the scintigraphic findings remained unexplained when fibrosis, periosteal reaction, granulocytic infiltration, and new bone formation were considered separately. In half of the cases the early scintigraphies revealed decreased uptake on the affected side, but this finding did not predict whether the final scintigraphy was positive. Finally, positivity was obvious in all cases, and a continuous range from negative to positive could not be documented. Present findings are a characteristic feature of the model. The physiological mechanism remains to be explained by independent measurements of relative bone blood flow made simultaneously with the scintigraphy and other bone tissue specific factors.