Sclerosis on sacroiliac xray?

Depends: If it is on both sides of the joint and there is joint space narrowing it may represent an inflammatory condition called sacroiliitis. Sclerosis itself is nonspecific and could represent degenerative change, a bone island or metastatic disease.

Sometimes arthritis: Sclerosis at sacroiliac joints can indicate an arthritic change. Sometimes this area of involvement is associated with some autoimmune inflammatory bowel diseases such as crohns disease and ulcerative colitis. Reactive arthritis is also possible, Probably most of time sclerosis coincidental finding and patient asymptomatic.