Hi MAggie,
I should correct myself many people never have true fusion in the S.I joints but they do have what they call erosions.I have no fusion after 20 years, I can still touch my toes but my last Bone density showed I had 8 % increase in Bone in my spine, but not fused. The X-rays however do show a kind of blurring of the S.I joints,when it should look nice and clean.
Take Care,
Janet