Smoking and socio-economic status in the etiology and severity of Legg-Calvé-Perthes' disease

Background: The etiology of Legg-Calvé-Perthes disease is poorly understood. An association has been found in the past between Legg-Calvé-Perthes disease and smoking as well as low socio-economic status. Methods: A prospective study was carried out in which families with a child diagnosed with Legg-Calvé-Perthes' disease were interviewed about the presence and duration of household second-hand smoke exposure to children. A control group of randomly selected families seen at our institution were interviewed with identical questions. The radiographs of children with Legg-Calvé-Perthes disease were reviewed and classified according to the Herring lateral pillar classification system. Results: Thirty-eight of the 60 patients (63.3%) with Legg-Calvé-Perthes disease were noted to have at least one smoker living in the child's household with a mean of 1.03 smoker-years per year of life exposure to smoke. The median income of the patients with Legg-Calvé-Perthes disease was US$20 300. The median income of the patients in the control group was US$17 000. Thirty-eight of the 96 control patients (39.6%) were noted to have at least one smoker living in the child's household with a mean of 0.48 smoker-years per year of life. A significant association was noted between living with a smoker and Legg-Calvé-Perthes disease as well as between increasing smoke exposure and increased risk of developing Legg-Calvé-Perthes disease. No significant association was noted between lower income and Legg-Calvé- Perthes disease. There was no association between increased smoke exposure and increased severity of Legg-Calvé-Perthes disease as measured by the lateral pillar classification. Conclusions: The presence of second-hand smoke seems to be a significant risk factor in the development of Legg-Calvé- Perthes disease. The presence of second-hand smoke may represent the 'unknown industrial factor' that has been discussed.