RESUMO
PURPOSE: The containment orientated treatment of Legg-Calvé-Perthes disease (LCPD) affected hip joints is broadly accepted in the literature. The prerequisite is early recognition of loss of containment. An often-used quantitative MRI containment parameter is the cartilaginous acetabulum-head-index (CAHI). Based on ultrasound (US), we analyzed the newly created 'femoral head extrusion angle' (HA) as a containment parameter in comparison with the CAHI in severe LCPD. METHODS: In a prospective study with 40 children (mean age 5.8 years sd 2.3) with unilateral LCPD classified as Catterall group III/IV, we measured the CAHI versus HA to assess the containment of the femoral head. HA in US was determined by the tangent from the bony acetabular rim to the cartilaginous cranio-lateral femoral head. RESULTS: The HA was significantly higher in LCPD-affected hip joints (25° sd 7°) than in healthy ones (13° sd 5°; p < 0.001). Correlation analysis of all hip joints revealed a significant correlation between HA and CAHI (r = -0.69; p < 0.001). Hip joints with a low CAHI indicating loss of containment showed a higher HA in sonography. CONCLUSION: The results of our study suggest that the HA in US is a reliable containment parameter in severe LCPD with a HA > 22° defining a pathologic value. In comparison with the CAHI, HA measurement in ultrasound is easier than the assessment of various parameters to calculate an index. Frequent sonographical follow-up assessment in critical joints is an alternative if MRI is not available, helping to detect an impending loss of containment early enough. LEVEL OF EVIDENCE: Level II.
RESUMO
PURPOSE: The objective of the present study was to investigate whether the sonographic visualization of lateralization of the femoral head is comparable to magnetic resonance imaging (MRI) and would therefore be able to contribute to the diagnosis of containment in patients with Perthes disease. MATERIALS AND METHODS: 46 patients with unilateral Perthes disease (age: 5.9 +/- 2.3 years) of Catterall group III/IV were evaluated at first presentation by means of ultrasound (US) and MRI of both hip joints to evaluate the morphology of the acetabular lip (LA) and the epiphysis (EP). The diagnosis of containment was performed in MRI as well as in US by the protrusion and deformity of the epiphysis of the femoral head with cranialization of the labrum. The evaluation of the sonographic and MRI findings was carried out independently by three observers (high experience: 1, 2, low experience: 3). Statistical analysis was performed using Cohen's non-weighted kappa kappa (kappa > 0.75 very high level of correlation). The study was conducted in accordance with the recommendations of the local ethics committee that approved our study. RESULTS: There was a high to very high agreement of the morphology of the LA and EP between observers 1 and 2 (MRI: LA: kappa = 0.87; EP: kappa = 0.90; US: LA kappa = 1.0; EP: kappa = 0.57). The comparison of observers 1 and 2 with observer 3 showed only a poor to acceptable level of agreement. US agreed well with MRI in the evaluation of the containment of the femoral head (1: kappa = 0.79; 2: kappa = 0.70, 3: kappa = 0.72). CONCLUSION: The results of our study suggest that US is a reliable examination method for monitoring the containment of the femoral head in Perthes disease. The evaluation of both methods depends on the experience of the observer.
