skip to main content

Mechanical vs Inflammatory Sacroiliitis — SCE Rheumatology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateMusculoskeletal ImagingMechanical vs Inflammatory SacroiliitisSCE Rheumatology

A 45-year-old man reports chronic low back and buttock pain that is worse after heavy manual work and at the end of the day. He has no prolonged morning stiffness, nocturnal pain, improvement with exercise, psoriasis, uveitis, inflammatory bowel disease or peripheral musculoskeletal features of spondyloarthritis. C-reactive protein is normal. A pelvic radiograph shows bilateral sacroiliac joint sclerosis and irregular joint-space narrowing with small inferior osteophytes, but no definite erosions or ankylosis. Which diagnosis best explains the sacroiliac joint appearances?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Mechanical degenerative sacroiliac joint disease related to repetitive loading

The best answer is C. The activity-related symptom pattern, heavy repetitive loading, normal CRP and absence of spondyloarthritis features favour mechanical disease. Sacroiliac degeneration may be bilateral and can produce sclerosis, joint-space irregularity or narrowing, osteophytes and occasionally strain-related bone marrow oedema, thereby mimicking inflammatory sacroiliitis. Radiographic axial spondyloarthritis is less likely because the clinical phenotype is mechanical and definite erosions or ankylosis are absent. Osteitis condensans ilii classically causes well-defined triangular iliac-sided sclerosis with preserved joint spaces rather than osteophytes and narrowing. Infection is usually acute, painful and commonly unilateral, with systemic or inflammatory features. Sacral insufficiency fractures are more typical in older or osteoporotic patients and do not explain this degenerative joint pattern. Imaging must therefore be interpreted in its clinical and morphological context.

Reference: Jurik AG et al. The sacroiliac joint across ages – what is normal? Therapeutic Advances in Musculoskeletal Disease. 2024;16. https://pubmed.ncbi.nlm.nih.gov/38559314/