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Avascular Necrosis — SCE Rheumatology MCQ

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ModerateMusculoskeletal ImagingAvascular NecrosisSCE Rheumatology

A 35-year-old woman with systemic lupus erythematosus treated with long-term glucocorticoids develops progressive groin pain. A hip radiograph shows a subchondral crescent sign in the femoral head without secondary joint-space narrowing. MRI demonstrates a geographic subchondral lesion bounded by a serpiginous low-signal line on T1-weighted images. Which diagnosis and staging system are most appropriate?

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Correct answer: C — Osteonecrosis of the femoral head; 2019 revised ARCO staging

The diagnosis is osteonecrosis (avascular necrosis) of the femoral head, staged using the revised ARCO system. The serpiginous T1-hypointense boundary demarcates necrotic from viable bone, while the radiographic crescent sign represents a subchondral fracture and therefore indicates ARCO stage III; the absence of secondary osteoarthritis argues against stage IV. Glucocorticoid exposure is an important risk factor. Transient osteoporosis typically produces diffuse marrow oedema rather than a circumscribed serpiginous band. A femoral neck stress fracture has a fracture-line pattern and is not classified by Neer. Pigmented villonodular synovitis is primarily synovial and characteristically shows haemosiderin-related low signal or blooming. Osteoarthritis would instead show joint-space loss and osteophytes.

Reference: Yoon BH et al. The 2019 Revised Version of Association Research Circulation Osseous Staging System of Osteonecrosis of the Femoral Head. Journal of Arthroplasty. 2020;35:933–940. https://pubmed.ncbi.nlm.nih.gov/31866252/