Diagnostic radiology in Legg-Calvé-Perthes disease.

Abstract

To assess lateral subluxation of the femoral head, the acetabulum-head index (AHI) was determined on 37 bilateral radiographs and arthrograms from children with unilateral Legg-Clavé-Perthes disease (LCPD). To establish reliable normal limits for the AHI, the non-affected hip was regarded as normal material. On radiographs, the lower normal rate was 80.7. On arthrograms, if the bony acetabular edge was used as the lateral margin of the acetabulum, the lower normal rate was 68.4 and if the labrum was used as landmark, the corresponding rate was 86. To establish normal medial joint space (MJS) and migration percentage (MP) values, 166 hip radiographs from 83 healthy children aged between 3 and 12 years were evaluated. The MJS values varied according to age and sex, the mean upper normal value being 11.2 mm; MP values were dependent on age only, the mean upper normal value being 20.8. Specific upper normal MJS and MP values were established for each age and sex group. To determine the corresponding values on arthrograms, the arthrograms and radiographs of the contralateral hips of 37 children with unilateral LCPD were used, the upper normal MJS and MP values being 5.7 and 31, respectively, which were unrelated to either age or sex. By using these normal values on the radiographs and arthrograms of the 37 affected hips, we found MP to be the best method for detecting whether or not a Perthes hip was contained within the acetabulum. The role of conventional radiography and bone scintigraphy was investigated in predicting the radiological outcome of LCPD in 75 children (86 hips). Bone scintigraphy provided more accurate information concerning the extent of the necrotic process than did the initial radiographs. Moreover it could reveal revascularization and consequently the stage of the disease. Revascularization may occur as early as one month after the onset of symptoms. However, the method was unable to predict the outcome of the disease in some of the cases, especially when it was performed late after the onset of symptoms. Conventional radiography provides important information about other parameters, such as "head-at-risk" signs, which facilitate treatment selection. Of these signs, not only lateral subluxation but also metaphyseal changes strongly predispose to severe deformity of the hip joint. In a prospective study of 22 patients (24 hips) with LCPD, the early conventional radiographs, arthrograms, bone scans and MR images were evaluated. MR imaging gave earlier and more reliable information about the real extent of necrosis of the femoral head, compared with radiography and scintigraphy. Furthermore, revascularization could be more clearly demonstrated on MR images than on scintigrams. MR imaging and arthrography were alike, however, as regards to reveal lateral subluxation, while radiography was less sensitive. The value of MR imaging for assessing the configuration and structure of the femoral head was investigated in comparison with radiography in 10 patients with healed LCPD. MR imaging provided no further important information, compared to radiography. Moreover, the relationship between radiological and clinical results was investigated, but there was insufficient correlation between radiological findings and clinical outcome. Most of the patients did well even though their hip images showed considerable changes.