MR:
Normally red marrow enahnces more than yellow marrow
Normal marrow enhances rapidly, but the ischaemic areas do not show enhancement. There may be enhancement around the ischaemic area
MR progression:
Normal to uniform edema
Subchondral non-enhancement or enhancement,
Low intensity zone surrounded by high signal
Crescent sign
Diffuse enhancement
Sequestration
Cortical collapse
Joint space narrowing
Secondary OA
MR pathology:
Fat - high T1, int T2 - stage 1/2
Blood - High t1 and T2 - stage 1/2
Fluid - low T1 and high t2 - stage 3/4
Fibrosis/bone - Low T1 and T2 - stage 3/4
Plain film:
Plain film staging:
Stage 0: normal
Stage 1: normal or patchy penia
Stage 2: lucent and sclerotic changes
Stage 3: crescent sign - subchondral collapse
Stage 4: stage 3 + OA, narrow joint space
Stage A,B,C:
A - <> 30% involement or > 4 mm head depression
ARCO classification is used
Plain radiograph:
Stage II: Sensitivity 88%, specificity 90%
Stage III: sensitivity 79%, specificity 82%
Stage IV: sensitivity 76%, specificty 100%
Agreement between plain films and MR:
80% for staging
70% for recording the location
67% for evaluating the size
79% for collapse of articular surface
56% for the degree of collapse
2. Malizos KN. Osteonecrosis of the femoral head: Etiology, imaging and treatment. European Journal of Radiology. Volume 63, Issue 1, July 2007, Pages 16-28 : Review article
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