IMAGING EVALUATION OF SUBLUXATION IN LEGG-CALVE-PERTHES-DISEASE - MAGNETIC-RESONANCE-IMAGING COMPARED WITH THE PLAIN RADIOGRAPH

The aim of the study was to evaluate the advantages of magnetic resona nce imaging (MRI) in determining subluxation in Legg-Calve-Perthes (LC PD) disease. Twenty six patients with unilateral LCPD received 33 MRI and plain radiographs. For each patient, acetabulum head index (AHI) w as measured on both hips (affected and unaffected) in a blinded fashio n. Measurements were made from the cortical bone margin on the plain r adiograph and from the cartilaginous surfaces on MRI. On the unaffecte d side AHI was 92.8% on the plain radiograph and 85% on MRI. On the af fected side, AHI was 87% on the plain radiograph and 77% on MRI. These differences were statistically significant. With regard to the unaffe cted side, the femoral head should be considered subluxated if AHI is less than 86% on the plain radiograph and less than 77% on MRI. On the affected side, in 14 cases the femoral head was well-contained on bot h the plain radiograph and MRI. In 11 patients the femoral head was su bluxated both on the plain radiograph and on MRI. In 8 patients the fe moral head was well-contained on the plain radiograph but subluxated o n MRI. This was due to thickening of the cartilaginous portion of the femoral head, which was clearly seen on MRI. MRI appeared to be more s ensitive in determining the subluxation of the femoral head during the active phase of LCPD.