MRI study on predicting the collapse of avascular necrosis of the femoral head

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Objective TostudytheriskfactorsofMRIforthepredictionofcollapseinpatients withavascularnecrosisofthefemoralhead. Methods Twenty-twopatients (39hips) diagnosed avascularnecrosisoffemoralheadbyMRwereenrolledinourstudy.ThefollowingMRappearances wereevaluated:bonemarrowedema,jointfluids,signalintensityandlocationofthelesion.The volumeandsurfaceareaofthenecrosiszonewerecalculated.Thetimeoffollow-upwas18—84 months (median,25months).LogisticregressionanalysiswasusedtopredicttheriskfactorsbySPSS 13.0.ThemaximumvalueofYoudenindexwasselectedasthecriticalpointtopredictthecollapseof femoralheadandtodefinethesensitivity,specificityandaccuracy. Results Inthe39hipswith femoralheadnecrosis,21hipshadcollapse.Bilateralcollapseoccurredin5cases.In25hipswiththe necrosissurfacelargerthan25%,collapseoccurredin21 (84%) ;In8hipswiththevolumeoffemoral headnecrosislargerthan30%,collapseoccurredinallcases;1n33hipswiththenecrosislocatingat thesuperolateralquadrant,collapseoccurredin21 (63.6%) ;In22hipswithnecroticareasshowing heterogeneoussignalintensity,collapseoccurredin18 (81.8%) ;In25hipswithlargeamountofjoint effusion,collapseoccurredin16 (64%) ;in18hipswithbonemarrowedema,collapseoccurredin13 (65%).Joint fluid,heterogeneous signal intensity and lesions in the superolateral quadrant,volume ratio,and area ratio were the high risk factors,while bone marrow edema was a relatively low risk factor.The area under ROC curves for area ratio of NASA was greater than that for volume ratio (0.987 vs 0.902).When the critical value for area ratio was 26.7%,the true positive rate was 95.2%,true negative rate was 94.4%,and Youden's index was 0.896. Conclusions The collapse of necrosis of femoral head may result from many factors.The femoral head was easy to collapse when it had large enough area of necrosis and mixed signal intensity,a large amount of joint effusion,bone marrow edema,and superolateral quadrant location.The critical value for area ratio to predict the collapse of femoral head was about 26.7%.The area ratio is more accurate than volume ratio in predicting the collapse of necrosis of femoral head. Key words: Femur head necrosis; Magnetic resonance imaging; Structure collapse; Forecasting