Osteomalacia means "soft bones". The bones are about half mineral (calcium and phosphate) and half protein matrix, which is called osteoid. Normally 98% of the osteoid is mineralized, and 2% is new osteoid that has just been made and is waiting to get mineralized. In osteomalacia, the mineral does not deposit in the osteoid normally, so extra osteoid accumulates. This happens because there is not enough mineral supplied to the bone, or because there is a problem with the osteoblasts. Collagen without mineral is soft and flexible, like your ears.
|Rickets occurs when this process takes place at the growth plates. The cartilage is mineralizing at a rapid rate. (This was illustrated in the page about bone growth). When the growth plate can't mineralize, it becomes thick, wide and irregular. The ends of the bones become weak and painful, especially at the knees which are bowed and fragile. The photograph above shows a group of children from Scotland who had rickets caused by too little vitamin D.|
Children with mineralizing problems have both rickets and osteomalacia. Adults who develop the disease after they have grown will have only osteomalacia, because they no longer have growth plates. They can have painful bones which break easily. The photograph at right shows an adult who had rickets as a child. Below is an xray from a child with rickets, showing bowed legs; bones near the knee are fuzzy and wide.
Rickets and osteomalacia have several causes. The most common is vitamin D deficiency, seen when people do not get enough sunlight exposure and also don't have vitamin D in their diet. People with liver or kidney disease have problems with vitamin D because they can't convert it to the active form. Some people inherit problems with vitamin D or with function of the osteoblasts. Low blood phosphate also causes osteomalacia, and this can be caused by inherited problems with the kidneys, certain kidney diseases, or side effects of drugs. In Japan, people who lived in a town near a cadmium factory started having problems with very painful bones, and they called the disease "itai-itai" disease, which can be translated to "ouch-ouch". The cadmium had caused kidney problems which resulted in low phosphate which caused the osteomalacia.
Photograph courtesy of Brendan Boyce
|Back to Diseases|