Significance of enhanced MRI in evaluating the prognosis of early Perthes disease

Abstract

Objective To investigate the reproducibility of the femoral head perfusion index by enhanced MRI and the predictive value of the Herring lateral pillar classification after the progression of early stage of Perthes disease (X-ray modified Waldenstrom stage Ia, Ib, IIa) to stage IIb. Methods From October 2016 to November 2018, a total of 30 children with early stage of Perthes disease were enrolled, including 29 males and 1 female, aged 7.5±1.0 years (range 6.3 to 9.5 years). All patients were evolved by unilateral with left 24 cases and 6 cases on the right side. There were 1 case in stage Ia, 16 cases in stage Ib and 13 cases in stage IIa. At the initial evaluation, X-ray films and enhanced MRI were performed. Three observers measured the femoral head perfusion index on the enhanced MRI. The ratio of the pixels in the affected ossified nucleus perfusion area to the pixels in the contralateral femoral skull nucleus was recorded. A total of 30 cases were measured with repeated evaluation at intervals of 1 to 2 weeks. The second measurement was independent of the first measurement results. The average of the two measurements was regarded as the final measurement results. At 3 months follow-up, anteroposterior and Lauenstein frog-lateral radiographs were taken. The follow-up duration was end at the stage IIb progression. The Herring lateral pillar of the femoral head was determined on the X-ray films. The differences in the early MRI femoral head perfusion index were compared between the different lateral column types. Results The ICC values of the femoral head perfusion index between the three observers were 0.876. The ICC values measured by the 1/3 perfusion index of the lateral femoral head were 0.729. The ICC values of the femoral head perfusion index measured by the same observer at different times were 0.932. The ICC values measured by the 1/3 perfusion index of the lateral femoral head were 0.805. A total of 30 children were followed to stage IIb at 6.49±5.12 months (range 2.3 to 22.1 months). There were 13 cases of type A and type B and 17 cases of type C. The sputum perfusion index of type A and type B was 59.77%±17.12% (range 25%-85%), and that of group C was 13.47%±10.65% (range 2%-23%). The difference between groups was statistically significant (t=8.563, P=0.000). The 1/3 perfusion index of the lateral femoral head of the A and B groups was 75.62%±15.03% (range 50%-95%), while the C type was 22.24%±12.28% (range 5%-45%) with significant difference (t=10.621, P=0.000). Conclusion The measurement of femoral head perfusion index on enhanced MRI has almost perfect agreement between and within observers across multiple rounds of study. In children with early Perthes disease, enhanced MRI has predictive effect on the Herring lateral pillar classification after progression to stage IIb. Key words: Magnetic resonance imaging; Subtraction technique; Child; Femur head necrosis; Forecasting