Coxa magna quantification using MRI in Legg-Calve-Perthes disease.

BACKGROUND: The idiopathic avascular necrosis of the femoral epiphysis characterizes the Legg-Calve-Perthes disease in pediatric osteoarticular pathologies. The coxa magna, more frequently observed, corresponds to an enlargement and deformation of the femoral head. The volume extension induces a subluxation of the hip, which is a bad prognosis for the healthy function of the joint.

METHODS: The aim of the study was to quantify the coxa magna in Legg-Calve-Perthes disease using magnetic resonance imaging. Twenty-five patients with unilateral Legg-Calve-Perthes disease were included in the clinical protocol and the volume properties of cartilaginous epiphyseal head were quantified using custom-made image processing software.

FINDINGS: Difference in cartilage volume between healthy hips and pathological ones were significant. Excepting one patient, we observed a statistically significant volume increase for the pathological hip, the mean value being +13%.

INTERPRETATION: Our results confirmed the effective three-dimensional properties of the coxa magna, which is clearly associated to a negative prognosis for the future of the joint. To our knowledge, the volume quantification of coxa magna has not been established before. The non-radiant MRI associated to three-dimensional investigation could potentially improve the clinical follow up of children to adapt the non-invasive treatment and to plan the surgery if necessary.