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📌 Osteonecrosis
- Osteonecrosis is an umbrella term that includes bone infarcts (metaphyseal) and avascular necrosis (epiphyseal).
- The term "osteonecrosis" is preferred for describing regions of devitalized bone because it is more inclusive than "avascular necrosis" and because all necrosis is by definition avascular.
✅ Double-Line Sign
- The double-line sign is seen on T2-weighted and intermediate-weighted MR images.
- It consists of an inner high-signal intensity band (vascularized granulation tissue, or the “creeping zone of substitution”) and an outer low-signal intensity band (sclerotic appositional new bone).
- It has been identified in 65–85% of patients and is considered pathognomonic of osteonecrosis.
- However, recent suggestions indicate that this double-line sign may be related to a chemical shift artifact.
- Histologic Characteristics: Chronic or healing phase osteonecrosis occurs in three zones:
- This rim at the epiphysis represents reparative tissue formed around a crescentic, wedge-shaped, or ringlike region of osteonecrosis.
✅ Mummified fat or yellow marrow
- Regions of osteonecrosis typically consist of central mummified fat or yellow marrow outlined by a distinct uninterrupted rim of primarily low signal intensity.
✅ Early Uncomplicated Osteonecrosis
- The earliest finding of avascular necrosis (AVN) in the hip and knee is a subchondral wedge-shaped, crescent-shaped, or roundish area bordered by a band-like zone of low T1-weighted signal intensity.
References
- AJR 2019; 213:963–982
- RadioGraphics 2018; 38:1478–1495
- Japanese Journal of Radiology (2022) 40:443–457
- Semin Musculoskelet Radiol. 2023 Feb;27(1):45-53
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#Osteonecrosis, #BoneInfarcts, #AvascularNecrosis, #DoubleLineSign, #MRI, #HistologicCharacteristics, #ChronicOsteonecrosis, #HealingPhase, #EarlyAVN, #Radiology
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