The scintigraphy of sacroiliac joints

Abstract

The accumulation of^99mTc-methylene diphosphonate (99mTc-MDP) and^99mTc-dicarboxypropane diphosphonate (^99mTc-DPD) in sacroiliac (si) joints was evaluated as a function of imaging time in 22 control patients and 5 patients with sacroiliitis. The controls were injected with either^99mTc-DPD or^99mTc-MDP (12 and 10 patients, respectively) and the patients with sacroiliitis with both agents within 5 days. Both the anterior and posterior views of the si joints were taken. The sacroiliac joint-to-sacrum (SI/S) ratio was calculated with the region of interest method. No statistically significant differences between these bone-seeking agents were found in the SI/S ratios of the control or the diseased patients. A clear overlap of indices (mean ± SD) was found between the control patients and the patients with sacroiliitis. When the inflamed si joint was divided into three small adjacent areas and the SI/S ratios calculated for these areas, a statistically significant (P < 0.001) increase in the SI/S ratio was noticed when compared with the SI/S ratio of the whole joint. Comparison of control patients and patients with sacroiliitis showed the most significant differences in the anterior views as well as in theP value:P < 0.001 in all patients injected with^99mTc-DPD and in most patients injected with^99mTc MDP. In the posterior views, the significance was less marked. In every case, the inflamed part of the si joint was visible in the anterior views. The background subtraction had the greatest effect on the SI/S ratio of anterior images, but in the posterior views no significance was found. The low specificity of sacroiliac joint imaging must be taken into consideration when the results are interpreted.