Remarks on the etiology and pathogenesis of Perthes' disease: an experiment-based hypothesis.

The literature on Perthes' disease points up the significance of specific anatomical conditions affecting vascularization of the femoral head, as well as immaturity and mechanical weakening of the bone tissue in the etiology and pathogenesis of this disorder in children. An experimental study using calf femurs as models confirmed the author's hypothesis that the areas most susceptible to mechanical stress are found in the immature subchondrial layer of the head and neck of the femoral bone. Further investigation of the results suggested that disturbances in the activity of the two growth zones (the epiphyseal growth cartilage and the growth plate) of the proximal femur contribute significantly to the etiology of Perthes' disease. The temporary abnormalities detected radiologically in the healthy femoral heads in about 30% of patients with unilateral Perthes' disease but without clinical symptoms are probably caused by temporary disturbances in the blood supply to these growth layers. These changes are radiological risk factors potentially leading to Perthes' disease. The author concludes that impaired blood flow within the growth layers additionally weakens the immature bone tissue of the femoral head and neck, which may lead to mechanical damage of the bone tissue itself, as well as to the epiphyseal blood vessels entering bony epiphysis. Gradual mechanical destruction of blood vessels in the area of the immature bone tissue below the epiphyseal growth cartilage can eventually initiate the irreversible onset of Perthes' disease.