During three to six months of lactation a woman's bone mineral density falls by 3-5% in the lumbar spine and femoral neck and 1-2% in the whole body, but the loss is transient. Giving calcium supplements during lactation has little or no effect (New England Journal of Medicine 1997;337:523-8, 558-9), and it seems that the temporary mobilisation and later restitution of the bone mineral are independent of the dietary intake of calcium.

Presented with a patient with a troublesome knee, a surgeon has to choose between ordering a magnetic resonance imaging scan or proceeding directly to arthroscopy. A review in the Journal of Bone and Joint Surgery (1997;79B:520) concludes that magnetic resonance imaging is a reliable alternative to diagnostic arthroscopy and is cheaper: so if a surgically treatable lesion seems unlikely then the scan should be the first choice.

One of the most frequent questions asked by patients told they have cancer is how long they may expect to live. A type of computer program called an artificial neural network has been shown to give better estimates of life expectancy for patients with colorectal cancer than those given by their surgeons (Lancet 1997;350:469-72). The networks were supplied with data on 42 variables collected …