Explaining case 26 of the ASAS Online Case Library

This is a case of osteoarthritis of the sacroiliac joints.
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Although the patient describes back pain of the inflammatory character, some details in the history already indicate a potential mechanical/degenerative cause: complaints onset after delivery, good spinal mobility, no CRP elevation, HLA-B27 negativity
MRI images were initially described as erosive sacroiliitis with active changes, and therefore the patient was referred to the university rheumatology outpatient clinic. Radiographs were supplemented but showed no evidence of structural changes in the sacroiliac joints. Lateral radiographs reveal a persistent disc in segment S1/2 of the sacrum.
MRI images, as far as can be judged with mediocre quality, show no major erosions in the T1-weighted image, but fat metaplasia of the para-articular bone marrow at the left sacroiliac joint, but located fairly dorsally. There appears to be sclerosis on the right dorsocaudal side. The STIR sequence shows bone marrow edema in the right sacroiliac joint (SIJ). Again, it is striking that the edema is very localized only in the dorsocaudal joint region and does not clearly affect several adjacent slices.
Because of the unclear situation, a low-dose computed tomography was obtained. This proved that no erosions were present in either SIJ. It is also apparent that a shape variant exists, especially on the right side, in the sense of an accessory articular facet dorsocaudally. Degenerative changes are also detectable on the left dorsocaudal side consisting of subchondral cysts in the bone. Mild subchondral sclerosis is present on both sides.
Complaints are additionally caused by osteochondrosis and facet joint arthrosis, see sagittal reconstruction of the CT scan.
#osteoarthritis #sacroiliacjoint #asas