Sacro-iliac joint scanning with technetium-99 diphosphonate.

Quantitative sacro-iliac (SI) joint scanning with methylene diphosphonate labelled with technetium-99 (99TcMDP) was performed in 25 control patients, in 16 patients with definite ankylosing spondylitis, in 23 patients with mechanical low back pain, and in 12 patients with seronegative arthritis. The mean radio-isotope index in the control group was 1.2 +/- 0.15. The highest value was 1.5. Values in excess of 1.5 were seen in patients with clinically active ankylosing spondylitis but not those with inactive disease. Three of the 12 seronegative arthritis patients (without clinical or radiological evidence of sacro-iliitis) had elevated values: all of these were positive for HL-A B27. An important finding was that six of the 23 patients with mechanical or non-specific low back pain had values above 1.5, unassociated with B27. These data emphasize the need for caution in the interpretation of abnormal sacro-iliac scans. Radio-isotope bone scanning can provide a qualitative and quantitative assessment of inflammatory activity in joints with minimal radiation exposure. Various authors have shown its value in providing early evidence of sacro-iliitis (Russell et al., 1975; Namey et al., 1977). In this study, methylene diphosphonate labelled with technetium-99 (99TcMMDP) has been used to produce quantitative sacro-iliac scans in order to evaluate sacro-iliac disease in four groups of patients presenting with or without low back pain.