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.