1. Bone changes in the haemoglobinopathies are caused by either (a) chronic haemolysis with marrow hyperplasia, or (b) infarction, when Hb S is present in the red cells in amounts sufficient to allow sickling (and therefore vascular occlusion) 2. Marrow hyperplasia produces osteoporosis, widening of the medulla, and thinning of the cortex; it may lead to spontaneous fractures and disturbances of growth. Enlargement of the foramina of the nutrient arteries may be seen especially in the phalanges. Infarcts leading to aseptic necrosis occur in the long bones, and may become infected with Salmonella organisms. The range of radiological lesions caused by these processes is illustrated.
